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This is autoconf.info, produced by makeinfo version 4.8 from
autoconf.texi.
This manual is for GNU Autoconf (version 2.61, 16 November 2006), a
package for creating scripts to configure source code packages using
templates and an M4 macro package.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.2 or any later version published by the Free Software
Foundation; with no Invariant Sections, with the Front-Cover texts
being "A GNU Manual," and with the Back-Cover Texts as in (a)
below. A copy of the license is included in the section entitled
"GNU Free Documentation License."
(a) The FSF's Back-Cover Text is: "You have freedom to copy and
modify this GNU Manual, like GNU software. Copies published by
the Free Software Foundation raise funds for GNU development."
INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Autoconf: (autoconf). Create source code configuration scripts.
END-INFO-DIR-ENTRY
INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* autoscan: (autoconf)autoscan Invocation.
Semi-automatic `configure.ac' writing
* ifnames: (autoconf)ifnames Invocation. Listing conditionals in source.
* autoconf: (autoconf)autoconf Invocation.
How to create configuration scripts
* autoreconf: (autoconf)autoreconf Invocation.
Remaking multiple `configure' scripts
* autoheader: (autoconf)autoheader Invocation.
How to create configuration templates
* autom4te: (autoconf)autom4te Invocation.
The Autoconf executables backbone
* configure: (autoconf)configure Invocation. Configuring a package.
* autoupdate: (autoconf)autoupdate Invocation.
Automatic update of `configure.ac'
* config.status: (autoconf)config.status Invocation. Recreating configurations.
* testsuite: (autoconf)testsuite Invocation. Running an Autotest test suite.
END-INFO-DIR-ENTRY

File: autoconf.info, Node: Top, Next: Introduction, Up: (dir)
Autoconf
********
This manual is for GNU Autoconf (version 2.61, 16 November 2006), a
package for creating scripts to configure source code packages using
templates and an M4 macro package.
Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.2 or any later version published by the Free Software
Foundation; with no Invariant Sections, with the Front-Cover texts
being "A GNU Manual," and with the Back-Cover Texts as in (a)
below. A copy of the license is included in the section entitled
"GNU Free Documentation License."
(a) The FSF's Back-Cover Text is: "You have freedom to copy and
modify this GNU Manual, like GNU software. Copies published by
the Free Software Foundation raise funds for GNU development."
* Menu:
* Introduction:: Autoconf's purpose, strengths, and weaknesses
* The GNU Build System:: A set of tools for portable software packages
* Making configure Scripts:: How to organize and produce Autoconf scripts
* Setup:: Initialization and output
* Existing Tests:: Macros that check for particular features
* Writing Tests:: How to write new feature checks
* Results:: What to do with results from feature checks
* Programming in M4:: Layers on top of which Autoconf is written
* Writing Autoconf Macros:: Adding new macros to Autoconf
* Portable Shell:: Shell script portability pitfalls
* Portable Make:: Makefile portability pitfalls
* Portable C and C++:: C and C++ portability pitfalls
* Manual Configuration:: Selecting features that can't be guessed
* Site Configuration:: Local defaults for `configure'
* Running configure Scripts:: How to use the Autoconf output
* config.status Invocation:: Recreating a configuration
* Obsolete Constructs:: Kept for backward compatibility
* Using Autotest:: Creating portable test suites
* FAQ:: Frequent Autoconf Questions, with answers
* History:: History of Autoconf
* Copying This Manual:: How to make copies of this manual
* Indices:: Indices of symbols, concepts, etc.
--- The Detailed Node Listing ---
The GNU Build System
* Automake:: Escaping makefile hell
* Gnulib:: The GNU portability library
* Libtool:: Building libraries portably
* Pointers:: More info on the GNU build system
Making `configure' Scripts
* Writing configure.ac:: What to put in an Autoconf input file
* autoscan Invocation:: Semi-automatic `configure.ac' writing
* ifnames Invocation:: Listing the conditionals in source code
* autoconf Invocation:: How to create configuration scripts
* autoreconf Invocation:: Remaking multiple `configure' scripts
Writing `configure.ac'
* Shell Script Compiler:: Autoconf as solution of a problem
* Autoconf Language:: Programming in Autoconf
* configure.ac Layout:: Standard organization of `configure.ac'
Initialization and Output Files
* Initializing configure:: Option processing etc.
* Notices:: Copyright, version numbers in `configure'
* Input:: Where Autoconf should find files
* Output:: Outputting results from the configuration
* Configuration Actions:: Preparing the output based on results
* Configuration Files:: Creating output files
* Makefile Substitutions:: Using output variables in makefiles
* Configuration Headers:: Creating a configuration header file
* Configuration Commands:: Running arbitrary instantiation commands
* Configuration Links:: Links depending on the configuration
* Subdirectories:: Configuring independent packages together
* Default Prefix:: Changing the default installation prefix
Substitutions in Makefiles
* Preset Output Variables:: Output variables that are always set
* Installation Directory Variables:: Other preset output variables
* Changed Directory Variables:: Warnings about `datarootdir'
* Build Directories:: Supporting multiple concurrent compiles
* Automatic Remaking:: Makefile rules for configuring
Configuration Header Files
* Header Templates:: Input for the configuration headers
* autoheader Invocation:: How to create configuration templates
* Autoheader Macros:: How to specify CPP templates
Existing Tests
* Common Behavior:: Macros' standard schemes
* Alternative Programs:: Selecting between alternative programs
* Files:: Checking for the existence of files
* Libraries:: Library archives that might be missing
* Library Functions:: C library functions that might be missing
* Header Files:: Header files that might be missing
* Declarations:: Declarations that may be missing
* Structures:: Structures or members that might be missing
* Types:: Types that might be missing
* Compilers and Preprocessors:: Checking for compiling programs
* System Services:: Operating system services
* Posix Variants:: Special kludges for specific Posix variants
* Erlang Libraries:: Checking for the existence of Erlang libraries
Common Behavior
* Standard Symbols:: Symbols defined by the macros
* Default Includes:: Includes used by the generic macros
Alternative Programs
* Particular Programs:: Special handling to find certain programs
* Generic Programs:: How to find other programs
Library Functions
* Function Portability:: Pitfalls with usual functions
* Particular Functions:: Special handling to find certain functions
* Generic Functions:: How to find other functions
Header Files
* Header Portability:: Collected knowledge on common headers
* Particular Headers:: Special handling to find certain headers
* Generic Headers:: How to find other headers
Declarations
* Particular Declarations:: Macros to check for certain declarations
* Generic Declarations:: How to find other declarations
Structures
* Particular Structures:: Macros to check for certain structure members
* Generic Structures:: How to find other structure members
Types
* Particular Types:: Special handling to find certain types
* Generic Types:: How to find other types
Compilers and Preprocessors
* Specific Compiler Characteristics:: Some portability issues
* Generic Compiler Characteristics:: Language independent tests and features
* C Compiler:: Checking its characteristics
* C++ Compiler:: Likewise
* Objective C Compiler:: Likewise
* Erlang Compiler and Interpreter:: Likewise
* Fortran Compiler:: Likewise
Writing Tests
* Language Choice:: Selecting which language to use for testing
* Writing Test Programs:: Forging source files for compilers
* Running the Preprocessor:: Detecting preprocessor symbols
* Running the Compiler:: Detecting language or header features
* Running the Linker:: Detecting library features
* Runtime:: Testing for runtime features
* Systemology:: A zoology of operating systems
* Multiple Cases:: Tests for several possible values
Writing Test Programs
* Guidelines:: General rules for writing test programs
* Test Functions:: Avoiding pitfalls in test programs
* Generating Sources:: Source program boilerplate
Results of Tests
* Defining Symbols:: Defining C preprocessor symbols
* Setting Output Variables:: Replacing variables in output files
* Special Chars in Variables:: Characters to beware of in variables
* Caching Results:: Speeding up subsequent `configure' runs
* Printing Messages:: Notifying `configure' users
Caching Results
* Cache Variable Names:: Shell variables used in caches
* Cache Files:: Files `configure' uses for caching
* Cache Checkpointing:: Loading and saving the cache file
Programming in M4
* M4 Quotation:: Protecting macros from unwanted expansion
* Using autom4te:: The Autoconf executables backbone
* Programming in M4sugar:: Convenient pure M4 macros
* Programming in M4sh:: Common shell Constructs
* File Descriptor Macros:: File descriptor macros for input and output
M4 Quotation
* Active Characters:: Characters that change the behavior of M4
* One Macro Call:: Quotation and one macro call
* Quotation and Nested Macros:: Macros calling macros
* Changequote is Evil:: Worse than INTERCAL: M4 + changequote
* Quadrigraphs:: Another way to escape special characters
* Quotation Rule Of Thumb:: One parenthesis, one quote
Using `autom4te'
* autom4te Invocation:: A GNU M4 wrapper
* Customizing autom4te:: Customizing the Autoconf package
Programming in M4sugar
* Redefined M4 Macros:: M4 builtins changed in M4sugar
* Looping constructs:: Iteration in M4
* Evaluation Macros:: More quotation and evaluation control
* Text processing Macros:: String manipulation in M4
* Forbidden Patterns:: Catching unexpanded macros
Writing Autoconf Macros
* Macro Definitions:: Basic format of an Autoconf macro
* Macro Names:: What to call your new macros
* Reporting Messages:: Notifying `autoconf' users
* Dependencies Between Macros:: What to do when macros depend on other macros
* Obsoleting Macros:: Warning about old ways of doing things
* Coding Style:: Writing Autoconf macros a` la Autoconf
Dependencies Between Macros
* Prerequisite Macros:: Ensuring required information
* Suggested Ordering:: Warning about possible ordering problems
* One-Shot Macros:: Ensuring a macro is called only once
Portable Shell Programming
* Shellology:: A zoology of shells
* Here-Documents:: Quirks and tricks
* File Descriptors:: FDs and redirections
* File System Conventions:: File names
* Shell Substitutions:: Variable and command expansions
* Assignments:: Varying side effects of assignments
* Parentheses:: Parentheses in shell scripts
* Slashes:: Slashes in shell scripts
* Special Shell Variables:: Variables you should not change
* Limitations of Builtins:: Portable use of not so portable /bin/sh
* Limitations of Usual Tools:: Portable use of portable tools
Portable Make Programming
* $< in Ordinary Make Rules:: $< in ordinary rules
* Failure in Make Rules:: Failing portably in rules
* Special Chars in Names:: Special Characters in Macro Names
* Backslash-Newline-Newline:: Empty last lines in macro definitions
* Backslash-Newline Comments:: Spanning comments across line boundaries
* Long Lines in Makefiles:: Line length limitations
* Macros and Submakes:: `make macro=value' and submakes
* The Make Macro MAKEFLAGS:: `$(MAKEFLAGS)' portability issues
* The Make Macro SHELL:: `$(SHELL)' portability issues
* Comments in Make Rules:: Other problems with Make comments
* obj/ and Make:: Don't name a subdirectory `obj'
* make -k Status:: Exit status of `make -k'
* VPATH and Make:: `VPATH' woes
* Single Suffix Rules:: Single suffix rules and separated dependencies
* Timestamps and Make:: Subsecond timestamp resolution
`VPATH' and Make
* VPATH and Double-colon:: Problems with `::' on ancient hosts
* $< in Explicit Rules:: `$<' does not work in ordinary rules
* Automatic Rule Rewriting:: `VPATH' goes wild on Solaris
* Tru64 Directory Magic:: `mkdir' goes wild on Tru64
* Make Target Lookup:: More details about `VPATH' lookup
Portable C and C++ Programming
* Varieties of Unportability:: How to make your programs unportable
* Integer Overflow:: When integers get too large
* Null Pointers:: Properties of null pointers
* Buffer Overruns:: Subscript errors and the like
* Volatile Objects:: `volatile' and signals
* Floating Point Portability:: Portable floating-point arithmetic
* Exiting Portably:: Exiting and the exit status
Manual Configuration
* Specifying Names:: Specifying the system type
* Canonicalizing:: Getting the canonical system type
* Using System Type:: What to do with the system type
Site Configuration
* Help Formatting:: Customizing `configure --help'
* External Software:: Working with other optional software
* Package Options:: Selecting optional features
* Pretty Help Strings:: Formatting help string
* Site Details:: Configuring site details
* Transforming Names:: Changing program names when installing
* Site Defaults:: Giving `configure' local defaults
Transforming Program Names When Installing
* Transformation Options:: `configure' options to transform names
* Transformation Examples:: Sample uses of transforming names
* Transformation Rules:: Makefile uses of transforming names
Running `configure' Scripts
* Basic Installation:: Instructions for typical cases
* Compilers and Options:: Selecting compilers and optimization
* Multiple Architectures:: Compiling for multiple architectures at once
* Installation Names:: Installing in different directories
* Optional Features:: Selecting optional features
* System Type:: Specifying the system type
* Sharing Defaults:: Setting site-wide defaults for `configure'
* Defining Variables:: Specifying the compiler etc.
* configure Invocation:: Changing how `configure' runs
Obsolete Constructs
* Obsolete config.status Use:: Different calling convention
* acconfig.h:: Additional entries in `config.h.in'
* autoupdate Invocation:: Automatic update of `configure.ac'
* Obsolete Macros:: Backward compatibility macros
* Autoconf 1:: Tips for upgrading your files
* Autoconf 2.13:: Some fresher tips
Upgrading From Version 1
* Changed File Names:: Files you might rename
* Changed Makefiles:: New things to put in `Makefile.in'
* Changed Macros:: Macro calls you might replace
* Changed Results:: Changes in how to check test results
* Changed Macro Writing:: Better ways to write your own macros
Upgrading From Version 2.13
* Changed Quotation:: Broken code which used to work
* New Macros:: Interaction with foreign macros
* Hosts and Cross-Compilation:: Bugward compatibility kludges
* AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token
* AC_FOO_IFELSE vs AC_TRY_FOO:: A more generic scheme for testing sources
Generating Test Suites with Autotest
* Using an Autotest Test Suite:: Autotest and the user
* Writing testsuite.at:: Autotest macros
* testsuite Invocation:: Running `testsuite' scripts
* Making testsuite Scripts:: Using autom4te to create `testsuite'
Using an Autotest Test Suite
* testsuite Scripts:: The concepts of Autotest
* Autotest Logs:: Their contents
Frequent Autoconf Questions, with answers
* Distributing:: Distributing `configure' scripts
* Why GNU M4:: Why not use the standard M4?
* Bootstrapping:: Autoconf and GNU M4 require each other?
* Why Not Imake:: Why GNU uses `configure' instead of Imake
* Defining Directories:: Passing `datadir' to program
* autom4te.cache:: What is it? Can I remove it?
* Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree
History of Autoconf
* Genesis:: Prehistory and naming of `configure'
* Exodus:: The plagues of M4 and Perl
* Leviticus:: The priestly code of portability arrives
* Numbers:: Growth and contributors
* Deuteronomy:: Approaching the promises of easy configuration
Copying This Manual
* GNU Free Documentation License:: License for copying this manual
Indices
* Environment Variable Index:: Index of environment variables used
* Output Variable Index:: Index of variables set in output files
* Preprocessor Symbol Index:: Index of C preprocessor symbols defined
* Autoconf Macro Index:: Index of Autoconf macros
* M4 Macro Index:: Index of M4, M4sugar, and M4sh macros
* Autotest Macro Index:: Index of Autotest macros
* Program & Function Index:: Index of those with portability problems
* Concept Index:: General index

File: autoconf.info, Node: Introduction, Next: The GNU Build System, Prev: Top, Up: Top
1 Introduction
**************
A physicist, an engineer, and a computer scientist were discussing the
nature of God. "Surely a Physicist," said the physicist, "because
early in the Creation, God made Light; and you know, Maxwell's
equations, the dual nature of electromagnetic waves, the relativistic
consequences..." "An Engineer!," said the engineer, "because
before making Light, God split the Chaos into Land and Water; it takes a
hell of an engineer to handle that big amount of mud, and orderly
separation of solids from liquids..." The computer scientist
shouted: "And the Chaos, where do you think it was coming from, hmm?"
--Anonymous
Autoconf is a tool for producing shell scripts that automatically
configure software source code packages to adapt to many kinds of
Posix-like systems. The configuration scripts produced by Autoconf are
independent of Autoconf when they are run, so their users do not need
to have Autoconf.
The configuration scripts produced by Autoconf require no manual user
intervention when run; they do not normally even need an argument
specifying the system type. Instead, they individually test for the
presence of each feature that the software package they are for might
need. (Before each check, they print a one-line message stating what
they are checking for, so the user doesn't get too bored while waiting
for the script to finish.) As a result, they deal well with systems
that are hybrids or customized from the more common Posix variants.
There is no need to maintain files that list the features supported by
each release of each variant of Posix.
For each software package that Autoconf is used with, it creates a
configuration script from a template file that lists the system features
that the package needs or can use. After the shell code to recognize
and respond to a system feature has been written, Autoconf allows it to
be shared by many software packages that can use (or need) that feature.
If it later turns out that the shell code needs adjustment for some
reason, it needs to be changed in only one place; all of the
configuration scripts can be regenerated automatically to take advantage
of the updated code.
The Metaconfig package is similar in purpose to Autoconf, but the
scripts it produces require manual user intervention, which is quite
inconvenient when configuring large source trees. Unlike Metaconfig
scripts, Autoconf scripts can support cross-compiling, if some care is
taken in writing them.
Autoconf does not solve all problems related to making portable
software packages--for a more complete solution, it should be used in
concert with other GNU build tools like Automake and Libtool. These
other tools take on jobs like the creation of a portable, recursive
makefile with all of the standard targets, linking of shared libraries,
and so on. *Note The GNU Build System::, for more information.
Autoconf imposes some restrictions on the names of macros used with
`#if' in C programs (*note Preprocessor Symbol Index::).
Autoconf requires GNU M4 in order to generate the scripts. It uses
features that some versions of M4, including GNU M4 1.3, do not have.
You should use version 1.4.7 or later of GNU M4.
*Note Autoconf 1::, for information about upgrading from version 1.
*Note History::, for the story of Autoconf's development. *Note FAQ::,
for answers to some common questions about Autoconf.
See the Autoconf web page (http://www.gnu.org/software/autoconf/)
for up-to-date information, details on the mailing lists, pointers to a
list of known bugs, etc.
Mail suggestions to the Autoconf mailing list <autoconf@gnu.org>.
Past suggestions are archived
(http://lists.gnu.org/archive/html/autoconf/).
Mail bug reports to the Autoconf Bugs mailing list
<bug-autoconf@gnu.org>. Past bug reports are archived
(http://lists.gnu.org/archive/html/bug-autoconf/).
If possible, first check that your bug is not already solved in
current development versions, and that it has not been reported yet.
Be sure to include all the needed information and a short
`configure.ac' that demonstrates the problem.
Autoconf's development tree is accessible via anonymous CVS; see the
Autoconf Summary (http://savannah.gnu.org/projects/autoconf/) for
details. Patches relative to the current CVS version can be sent for
review to the Autoconf Patches mailing list <autoconf-patches@gnu.org>.
Past patches are archived
(http://lists.gnu.org/archive/html/autoconf-patches/).
Because of its mission, the Autoconf package itself includes only a
set of often-used macros that have already demonstrated their
usefulness. Nevertheless, if you wish to share your macros, or find
existing ones, see the Autoconf Macro Archive
(http://autoconf-archive.cryp.to/), which is kindly run by Peter Simons
<simons@cryp.to>.

File: autoconf.info, Node: The GNU Build System, Next: Making configure Scripts, Prev: Introduction, Up: Top
2 The GNU Build System
**********************
Autoconf solves an important problem--reliable discovery of
system-specific build and runtime information--but this is only one
piece of the puzzle for the development of portable software. To this
end, the GNU project has developed a suite of integrated utilities to
finish the job Autoconf started: the GNU build system, whose most
important components are Autoconf, Automake, and Libtool. In this
chapter, we introduce you to those tools, point you to sources of more
information, and try to convince you to use the entire GNU build system
for your software.
* Menu:
* Automake:: Escaping makefile hell
* Gnulib:: The GNU portability library
* Libtool:: Building libraries portably
* Pointers:: More info on the GNU build system

File: autoconf.info, Node: Automake, Next: Gnulib, Up: The GNU Build System
2.1 Automake
============
The ubiquity of `make' means that a makefile is almost the only viable
way to distribute automatic build rules for software, but one quickly
runs into its numerous limitations. Its lack of support for automatic
dependency tracking, recursive builds in subdirectories, reliable
timestamps (e.g., for network file systems), and so on, mean that
developers must painfully (and often incorrectly) reinvent the wheel
for each project. Portability is non-trivial, thanks to the quirks of
`make' on many systems. On top of all this is the manual labor
required to implement the many standard targets that users have come to
expect (`make install', `make distclean', `make uninstall', etc.).
Since you are, of course, using Autoconf, you also have to insert
repetitive code in your `Makefile.in' to recognize `@CC@', `@CFLAGS@',
and other substitutions provided by `configure'. Into this mess steps
"Automake".
Automake allows you to specify your build needs in a `Makefile.am'
file with a vastly simpler and more powerful syntax than that of a plain
makefile, and then generates a portable `Makefile.in' for use with
Autoconf. For example, the `Makefile.am' to build and install a simple
"Hello world" program might look like:
bin_PROGRAMS = hello
hello_SOURCES = hello.c
The resulting `Makefile.in' (~400 lines) automatically supports all the
standard targets, the substitutions provided by Autoconf, automatic
dependency tracking, `VPATH' building, and so on. `make' builds the
`hello' program, and `make install' installs it in `/usr/local/bin' (or
whatever prefix was given to `configure', if not `/usr/local').
The benefits of Automake increase for larger packages (especially
ones with subdirectories), but even for small programs the added
convenience and portability can be substantial. And that's not all....

File: autoconf.info, Node: Gnulib, Next: Libtool, Prev: Automake, Up: The GNU Build System
2.2 Gnulib
==========
GNU software has a well-deserved reputation for running on many
different types of systems. While our primary goal is to write
software for the GNU system, many users and developers have been
introduced to us through the systems that they were already using.
Gnulib is a central location for common GNU code, intended to be
shared among free software packages. Its components are typically
shared at the source level, rather than being a library that gets built,
installed, and linked against. The idea is to copy files from Gnulib
into your own source tree. There is no distribution tarball; developers
should just grab source modules from the repository. The source files
are available online, under various licenses, mostly GNU GPL or GNU
LGPL.
Gnulib modules typically contain C source code along with Autoconf
macros used to configure the source code. For example, the Gnulib
`stdbool' module implements a `stdbool.h' header that nearly conforms
to C99, even on old-fashioned hosts that lack `stdbool.h'. This module
contains a source file for the replacement header, along with an
Autoconf macro that arranges to use the replacement header on
old-fashioned systems.

File: autoconf.info, Node: Libtool, Next: Pointers, Prev: Gnulib, Up: The GNU Build System
2.3 Libtool
===========
Often, one wants to build not only programs, but libraries, so that
other programs can benefit from the fruits of your labor. Ideally, one
would like to produce _shared_ (dynamically linked) libraries, which
can be used by multiple programs without duplication on disk or in
memory and can be updated independently of the linked programs.
Producing shared libraries portably, however, is the stuff of
nightmares--each system has its own incompatible tools, compiler flags,
and magic incantations. Fortunately, GNU provides a solution:
"Libtool".
Libtool handles all the requirements of building shared libraries for
you, and at this time seems to be the _only_ way to do so with any
portability. It also handles many other headaches, such as: the
interaction of Make rules with the variable suffixes of shared
libraries, linking reliably with shared libraries before they are
installed by the superuser, and supplying a consistent versioning system
(so that different versions of a library can be installed or upgraded
without breaking binary compatibility). Although Libtool, like
Autoconf, can be used without Automake, it is most simply utilized in
conjunction with Automake--there, Libtool is used automatically
whenever shared libraries are needed, and you need not know its syntax.

File: autoconf.info, Node: Pointers, Prev: Libtool, Up: The GNU Build System
2.4 Pointers
============
Developers who are used to the simplicity of `make' for small projects
on a single system might be daunted at the prospect of learning to use
Automake and Autoconf. As your software is distributed to more and
more users, however, you otherwise quickly find yourself putting lots
of effort into reinventing the services that the GNU build tools
provide, and making the same mistakes that they once made and overcame.
(Besides, since you're already learning Autoconf, Automake is a piece
of cake.)
There are a number of places that you can go to for more information
on the GNU build tools.
- Web
The home pages for Autoconf
(http://www.gnu.org/software/autoconf/), Automake
(http://www.gnu.org/software/automake/), Gnulib
(http://www.gnu.org/software/gnulib/), and Libtool
(http://www.gnu.org/software/libtool/).
- Automake Manual
*Note Automake: (automake)Top, for more information on Automake.
- Books
The book `GNU Autoconf, Automake and Libtool'(1) describes the
complete GNU build environment. You can also find the entire book
on-line (http://sources.redhat.com/autobook/).
---------- Footnotes ----------
(1) `GNU Autoconf, Automake and Libtool', by G. V. Vaughan, B.
Elliston, T. Tromey, and I. L. Taylor. SAMS (originally New Riders),
2000, ISBN 1578701902.

File: autoconf.info, Node: Making configure Scripts, Next: Setup, Prev: The GNU Build System, Up: Top
3 Making `configure' Scripts
****************************
The configuration scripts that Autoconf produces are by convention
called `configure'. When run, `configure' creates several files,
replacing configuration parameters in them with appropriate values.
The files that `configure' creates are:
- one or more `Makefile' files, usually one in each subdirectory of
the package (*note Makefile Substitutions::);
- optionally, a C header file, the name of which is configurable,
containing `#define' directives (*note Configuration Headers::);
- a shell script called `config.status' that, when run, recreates
the files listed above (*note config.status Invocation::);
- an optional shell script normally called `config.cache' (created
when using `configure --config-cache') that saves the results of
running many of the tests (*note Cache Files::);
- a file called `config.log' containing any messages produced by
compilers, to help debugging if `configure' makes a mistake.
To create a `configure' script with Autoconf, you need to write an
Autoconf input file `configure.ac' (or `configure.in') and run
`autoconf' on it. If you write your own feature tests to supplement
those that come with Autoconf, you might also write files called
`aclocal.m4' and `acsite.m4'. If you use a C header file to contain
`#define' directives, you might also run `autoheader', and you can
distribute the generated file `config.h.in' with the package.
Here is a diagram showing how the files that can be used in
configuration are produced. Programs that are executed are suffixed by
`*'. Optional files are enclosed in square brackets (`[]').
`autoconf' and `autoheader' also read the installed Autoconf macro
files (by reading `autoconf.m4').
Files used in preparing a software package for distribution:
your source files --> [autoscan*] --> [configure.scan] --> configure.ac
configure.ac --.
| .------> autoconf* -----> configure
[aclocal.m4] --+---+
| `-----> [autoheader*] --> [config.h.in]
[acsite.m4] ---'
Makefile.in -------------------------------> Makefile.in
Files used in configuring a software package:
.-------------> [config.cache]
configure* ------------+-------------> config.log
|
[config.h.in] -. v .-> [config.h] -.
+--> config.status* -+ +--> make*
Makefile.in ---' `-> Makefile ---'
* Menu:
* Writing configure.ac:: What to put in an Autoconf input file
* autoscan Invocation:: Semi-automatic `configure.ac' writing
* ifnames Invocation:: Listing the conditionals in source code
* autoconf Invocation:: How to create configuration scripts
* autoreconf Invocation:: Remaking multiple `configure' scripts

File: autoconf.info, Node: Writing configure.ac, Next: autoscan Invocation, Up: Making configure Scripts
3.1 Writing `configure.ac'
==========================
To produce a `configure' script for a software package, create a file
called `configure.ac' that contains invocations of the Autoconf macros
that test the system features your package needs or can use. Autoconf
macros already exist to check for many features; see *Note Existing
Tests::, for their descriptions. For most other features, you can use
Autoconf template macros to produce custom checks; see *Note Writing
Tests::, for information about them. For especially tricky or
specialized features, `configure.ac' might need to contain some
hand-crafted shell commands; see *Note Portable Shell::. The
`autoscan' program can give you a good start in writing `configure.ac'
(*note autoscan Invocation::, for more information).
Previous versions of Autoconf promoted the name `configure.in',
which is somewhat ambiguous (the tool needed to process this file is not
described by its extension), and introduces a slight confusion with
`config.h.in' and so on (for which `.in' means "to be processed by
`configure'"). Using `configure.ac' is now preferred.
* Menu:
* Shell Script Compiler:: Autoconf as solution of a problem
* Autoconf Language:: Programming in Autoconf
* configure.ac Layout:: Standard organization of `configure.ac'

File: autoconf.info, Node: Shell Script Compiler, Next: Autoconf Language, Up: Writing configure.ac
3.1.1 A Shell Script Compiler
-----------------------------
Just as for any other computer language, in order to properly program
`configure.ac' in Autoconf you must understand _what_ problem the
language tries to address and _how_ it does so.
The problem Autoconf addresses is that the world is a mess. After
all, you are using Autoconf in order to have your package compile
easily on all sorts of different systems, some of them being extremely
hostile. Autoconf itself bears the price for these differences:
`configure' must run on all those systems, and thus `configure' must
limit itself to their lowest common denominator of features.
Naturally, you might then think of shell scripts; who needs
`autoconf'? A set of properly written shell functions is enough to
make it easy to write `configure' scripts by hand. Sigh!
Unfortunately, shell functions do not belong to the least common
denominator; therefore, where you would like to define a function and
use it ten times, you would instead need to copy its body ten times.
So, what is really needed is some kind of compiler, `autoconf', that
takes an Autoconf program, `configure.ac', and transforms it into a
portable shell script, `configure'.
How does `autoconf' perform this task?
There are two obvious possibilities: creating a brand new language or
extending an existing one. The former option is attractive: all sorts
of optimizations could easily be implemented in the compiler and many
rigorous checks could be performed on the Autoconf program (e.g.,
rejecting any non-portable construct). Alternatively, you can extend
an existing language, such as the `sh' (Bourne shell) language.
Autoconf does the latter: it is a layer on top of `sh'. It was
therefore most convenient to implement `autoconf' as a macro expander:
a program that repeatedly performs "macro expansions" on text input,
replacing macro calls with macro bodies and producing a pure `sh'
script in the end. Instead of implementing a dedicated Autoconf macro
expander, it is natural to use an existing general-purpose macro
language, such as M4, and implement the extensions as a set of M4
macros.

File: autoconf.info, Node: Autoconf Language, Next: configure.ac Layout, Prev: Shell Script Compiler, Up: Writing configure.ac
3.1.2 The Autoconf Language
---------------------------
The Autoconf language differs from many other computer languages
because it treats actual code the same as plain text. Whereas in C,
for instance, data and instructions have different syntactic status, in
Autoconf their status is rigorously the same. Therefore, we need a
means to distinguish literal strings from text to be expanded:
quotation.
When calling macros that take arguments, there must not be any white
space between the macro name and the open parenthesis. Arguments should
be enclosed within the M4 quote characters `[' and `]', and be
separated by commas. Any leading blanks or newlines in arguments are
ignored, unless they are quoted. You should always quote an argument
that might contain a macro name, comma, parenthesis, or a leading blank
or newline. This rule applies recursively for every macro call,
including macros called from other macros.
For instance:
AC_CHECK_HEADER([stdio.h],
[AC_DEFINE([HAVE_STDIO_H], [1],
[Define to 1 if you have <stdio.h>.])],
[AC_MSG_ERROR([Sorry, can't do anything for you])])
is quoted properly. You may safely simplify its quotation to:
AC_CHECK_HEADER([stdio.h],
[AC_DEFINE([HAVE_STDIO_H], 1,
[Define to 1 if you have <stdio.h>.])],
[AC_MSG_ERROR([Sorry, can't do anything for you])])
because `1' cannot contain a macro call. Here, the argument of
`AC_MSG_ERROR' must be quoted; otherwise, its comma would be
interpreted as an argument separator. Also, the second and third
arguments of `AC_CHECK_HEADER' must be quoted, since they contain macro
calls. The three arguments `HAVE_STDIO_H', `stdio.h', and `Define to 1
if you have <stdio.h>.' do not need quoting, but if you unwisely
defined a macro with a name like `Define' or `stdio' then they would
need quoting. Cautious Autoconf users would keep the quotes, but many
Autoconf users find such precautions annoying, and would rewrite the
example as follows:
AC_CHECK_HEADER(stdio.h,
[AC_DEFINE(HAVE_STDIO_H, 1,
[Define to 1 if you have <stdio.h>.])],
[AC_MSG_ERROR([Sorry, can't do anything for you])])
This is safe, so long as you adopt good naming conventions and do not
define macros with names like `HAVE_STDIO_H', `stdio', or `h'. Though
it is also safe here to omit the quotes around `Define to 1 if you have
<stdio.h>.' this is not recommended, as message strings are more likely
to inadvertently contain commas.
The following example is wrong and dangerous, as it is underquoted:
AC_CHECK_HEADER(stdio.h,
AC_DEFINE(HAVE_STDIO_H, 1,
Define to 1 if you have <stdio.h>.),
AC_MSG_ERROR([Sorry, can't do anything for you]))
In other cases, you may have to use text that also resembles a macro
call. You must quote that text even when it is not passed as a macro
argument:
echo "Hard rock was here! --[AC_DC]"
which results in:
echo "Hard rock was here! --AC_DC"
When you use the same text in a macro argument, you must therefore have
an extra quotation level (since one is stripped away by the macro
substitution). In general, then, it is a good idea to _use double
quoting for all literal string arguments_:
AC_MSG_WARN([[AC_DC stinks --Iron Maiden]])
You are now able to understand one of the constructs of Autoconf that
has been continually misunderstood... The rule of thumb is that
_whenever you expect macro expansion, expect quote expansion_; i.e.,
expect one level of quotes to be lost. For instance:
AC_COMPILE_IFELSE([char b[10];], [], [AC_MSG_ERROR([you lose])])
is incorrect: here, the first argument of `AC_COMPILE_IFELSE' is `char
b[10];' and is expanded once, which results in `char b10;'. (There was
an idiom common in Autoconf's past to address this issue via the M4
`changequote' primitive, but do not use it!) Let's take a closer look:
the author meant the first argument to be understood as a literal, and
therefore it must be quoted twice:
AC_COMPILE_IFELSE([[char b[10];]], [], [AC_MSG_ERROR([you lose])])
Voila`, you actually produce `char b[10];' this time!
On the other hand, descriptions (e.g., the last parameter of
`AC_DEFINE' or `AS_HELP_STRING') are not literals--they are subject to
line breaking, for example--and should not be double quoted. Even if
these descriptions are short and are not actually broken, double
quoting them yields weird results.
Some macros take optional arguments, which this documentation
represents as [ARG] (not to be confused with the quote characters).
You may just leave them empty, or use `[]' to make the emptiness of the
argument explicit, or you may simply omit the trailing commas. The
three lines below are equivalent:
AC_CHECK_HEADERS([stdio.h], [], [], [])
AC_CHECK_HEADERS([stdio.h],,,)
AC_CHECK_HEADERS([stdio.h])
It is best to put each macro call on its own line in `configure.ac'.
Most of the macros don't add extra newlines; they rely on the newline
after the macro call to terminate the commands. This approach makes
the generated `configure' script a little easier to read by not
inserting lots of blank lines. It is generally safe to set shell
variables on the same line as a macro call, because the shell allows
assignments without intervening newlines.
You can include comments in `configure.ac' files by starting them
with the `#'. For example, it is helpful to begin `configure.ac' files
with a line like this:
# Process this file with autoconf to produce a configure script.

File: autoconf.info, Node: configure.ac Layout, Prev: Autoconf Language, Up: Writing configure.ac
3.1.3 Standard `configure.ac' Layout
------------------------------------
The order in which `configure.ac' calls the Autoconf macros is not
important, with a few exceptions. Every `configure.ac' must contain a
call to `AC_INIT' before the checks, and a call to `AC_OUTPUT' at the
end (*note Output::). Additionally, some macros rely on other macros
having been called first, because they check previously set values of
some variables to decide what to do. These macros are noted in the
individual descriptions (*note Existing Tests::), and they also warn
you when `configure' is created if they are called out of order.
To encourage consistency, here is a suggested order for calling the
Autoconf macros. Generally speaking, the things near the end of this
list are those that could depend on things earlier in it. For example,
library functions could be affected by types and libraries.
Autoconf requirements
`AC_INIT(PACKAGE, VERSION, BUG-REPORT-ADDRESS)'
information on the package
checks for programs
checks for libraries
checks for header files
checks for types
checks for structures
checks for compiler characteristics
checks for library functions
checks for system services
`AC_CONFIG_FILES([FILE...])'
`AC_OUTPUT'

File: autoconf.info, Node: autoscan Invocation, Next: ifnames Invocation, Prev: Writing configure.ac, Up: Making configure Scripts
3.2 Using `autoscan' to Create `configure.ac'
=============================================
The `autoscan' program can help you create and/or maintain a
`configure.ac' file for a software package. `autoscan' examines source
files in the directory tree rooted at a directory given as a command
line argument, or the current directory if none is given. It searches
the source files for common portability problems and creates a file
`configure.scan' which is a preliminary `configure.ac' for that
package, and checks a possibly existing `configure.ac' for completeness.
When using `autoscan' to create a `configure.ac', you should
manually examine `configure.scan' before renaming it to `configure.ac';
it probably needs some adjustments. Occasionally, `autoscan' outputs a
macro in the wrong order relative to another macro, so that `autoconf'
produces a warning; you need to move such macros manually. Also, if
you want the package to use a configuration header file, you must add a
call to `AC_CONFIG_HEADERS' (*note Configuration Headers::). You might
also have to change or add some `#if' directives to your program in
order to make it work with Autoconf (*note ifnames Invocation::, for
information about a program that can help with that job).
When using `autoscan' to maintain a `configure.ac', simply consider
adding its suggestions. The file `autoscan.log' contains detailed
information on why a macro is requested.
`autoscan' uses several data files (installed along with Autoconf)
to determine which macros to output when it finds particular symbols in
a package's source files. These data files all have the same format:
each line consists of a symbol, one or more blanks, and the Autoconf
macro to output if that symbol is encountered. Lines starting with `#'
are comments.
`autoscan' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Print the names of the files it examines and the potentially
interesting symbols it finds in them. This output can be
voluminous.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.

File: autoconf.info, Node: ifnames Invocation, Next: autoconf Invocation, Prev: autoscan Invocation, Up: Making configure Scripts
3.3 Using `ifnames' to List Conditionals
========================================
`ifnames' can help you write `configure.ac' for a software package. It
prints the identifiers that the package already uses in C preprocessor
conditionals. If a package has already been set up to have some
portability, `ifnames' can thus help you figure out what its
`configure' needs to check for. It may help fill in some gaps in a
`configure.ac' generated by `autoscan' (*note autoscan Invocation::).
`ifnames' scans all of the C source files named on the command line
(or the standard input, if none are given) and writes to the standard
output a sorted list of all the identifiers that appear in those files
in `#if', `#elif', `#ifdef', or `#ifndef' directives. It prints each
identifier on a line, followed by a space-separated list of the files
in which that identifier occurs.
`ifnames' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.

File: autoconf.info, Node: autoconf Invocation, Next: autoreconf Invocation, Prev: ifnames Invocation, Up: Making configure Scripts
3.4 Using `autoconf' to Create `configure'
==========================================
To create `configure' from `configure.ac', run the `autoconf' program
with no arguments. `autoconf' processes `configure.ac' with the M4
macro processor, using the Autoconf macros. If you give `autoconf' an
argument, it reads that file instead of `configure.ac' and writes the
configuration script to the standard output instead of to `configure'.
If you give `autoconf' the argument `-', it reads from the standard
input instead of `configure.ac' and writes the configuration script to
the standard output.
The Autoconf macros are defined in several files. Some of the files
are distributed with Autoconf; `autoconf' reads them first. Then it
looks for the optional file `acsite.m4' in the directory that contains
the distributed Autoconf macro files, and for the optional file
`aclocal.m4' in the current directory. Those files can contain your
site's or the package's own Autoconf macro definitions (*note Writing
Autoconf Macros::, for more information). If a macro is defined in
more than one of the files that `autoconf' reads, the last definition
it reads overrides the earlier ones.
`autoconf' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Remake `configure' even if newer than its input files.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
`--output=FILE'
`-o FILE'
Save output (script or trace) to FILE. The file `-' stands for
the standard output.
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list). *Note Reporting Messages::, macro
`AC_DIAGNOSE', for a comprehensive list of categories. Special
values include:
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
Warnings about `syntax' are enabled by default, and the environment
variable `WARNINGS', a comma separated list of categories, is
honored as well. Passing `-W CATEGORY' actually behaves as if you
had passed `--warnings=syntax,$WARNINGS,CATEGORY'. If you want to
disable the defaults and `WARNINGS', but (for example) enable the
warnings about obsolete constructs, you would use `-W
none,obsolete'.
Because `autoconf' uses `autom4te' behind the scenes, it displays
a back trace for errors, but not for warnings; if you want them,
just pass `-W error'. *Note autom4te Invocation::, for some
examples.
`--trace=MACRO[:FORMAT]'
`-t MACRO[:FORMAT]'
Do not create the `configure' script, but list the calls to MACRO
according to the FORMAT. Multiple `--trace' arguments can be used
to list several macros. Multiple `--trace' arguments for a single
macro are not cumulative; instead, you should just make FORMAT as
long as needed.
The FORMAT is a regular string, with newlines if desired, and
several special escape codes. It defaults to `$f:$l:$n:$%'; see
*Note autom4te Invocation::, for details on the FORMAT.
`--initialization'
`-i'
By default, `--trace' does not trace the initialization of the
Autoconf macros (typically the `AC_DEFUN' definitions). This
results in a noticeable speedup, but can be disabled by this
option.
It is often necessary to check the content of a `configure.ac' file,
but parsing it yourself is extremely fragile and error-prone. It is
suggested that you rely upon `--trace' to scan `configure.ac'. For
instance, to find the list of variables that are substituted, use:
$ autoconf -t AC_SUBST
configure.ac:2:AC_SUBST:ECHO_C
configure.ac:2:AC_SUBST:ECHO_N
configure.ac:2:AC_SUBST:ECHO_T
More traces deleted
The example below highlights the difference between `$@', `$*', and
`$%'.
$ cat configure.ac
AC_DEFINE(This, is, [an
[example]])
$ autoconf -t 'AC_DEFINE:@: $@
*: $*
%: $%'
@: [This],[is],[an
[example]]
*: This,is,an
[example]
%: This:is:an [example]
The FORMAT gives you a lot of freedom:
$ autoconf -t 'AC_SUBST:$$ac_subst{"$1"} = "$f:$l";'
$ac_subst{"ECHO_C"} = "configure.ac:2";
$ac_subst{"ECHO_N"} = "configure.ac:2";
$ac_subst{"ECHO_T"} = "configure.ac:2";
More traces deleted
A long SEPARATOR can be used to improve the readability of complex
structures, and to ease their parsing (for instance when no single
character is suitable as a separator):
$ autoconf -t 'AM_MISSING_PROG:${|:::::|}*'
ACLOCAL|:::::|aclocal|:::::|$missing_dir
AUTOCONF|:::::|autoconf|:::::|$missing_dir
AUTOMAKE|:::::|automake|:::::|$missing_dir
More traces deleted

File: autoconf.info, Node: autoreconf Invocation, Prev: autoconf Invocation, Up: Making configure Scripts
3.5 Using `autoreconf' to Update `configure' Scripts
====================================================
Installing the various components of the GNU Build System can be
tedious: running `autopoint' for Gettext, `automake' for `Makefile.in'
etc. in each directory. It may be needed either because some tools
such as `automake' have been updated on your system, or because some of
the sources such as `configure.ac' have been updated, or finally,
simply in order to install the GNU Build System in a fresh tree.
`autoreconf' runs `autoconf', `autoheader', `aclocal', `automake',
`libtoolize', and `autopoint' (when appropriate) repeatedly to update
the GNU Build System in the specified directories and their
subdirectories (*note Subdirectories::). By default, it only remakes
those files that are older than their sources.
If you install a new version of some tool, you can make `autoreconf'
remake _all_ of the files by giving it the `--force' option.
*Note Automatic Remaking::, for Make rules to automatically remake
`configure' scripts when their source files change. That method
handles the timestamps of configuration header templates properly, but
does not pass `--autoconf-dir=DIR' or `--localdir=DIR'.
Gettext supplies the `autopoint' command to add translation
infrastructure to a source package. If you use `autopoint', your
`configure.ac' should invoke both `AM_GNU_GETTEXT' and
`AM_GNU_GETTEXT_VERSION(GETTEXT-VERSION)'. *Note Invoking the
`autopoint' Program: (gettext)autopoint Invocation, for further details.
`autoreconf' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
Print the name of each directory `autoreconf' examines and the
commands it runs. If given two or more times, pass `--verbose' to
subordinate tools that support it.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Remake even `configure' scripts and configuration headers that are
newer than their input files (`configure.ac' and, if present,
`aclocal.m4').
`--install'
`-i'
Install the missing auxiliary files in the package. By default,
files are copied; this can be changed with `--symlink'.
If deemed appropriate, this option triggers calls to `automake
--add-missing', `libtoolize', `autopoint', etc.
`--no-recursive'
Do not rebuild files in subdirectories to configure (see *Note
Subdirectories::, macro `AC_CONFIG_SUBDIRS').
`--symlink'
`-s'
When used with `--install', install symbolic links to the missing
auxiliary files instead of copying them.
`--make'
`-m'
When the directories were configured, update the configuration by
running `./config.status --recheck && ./config.status', and then
run `make'.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
Passed on to `autoconf' and `autoheader' internally.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
Passed on to `autoconf' and `autoheader' internally.
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list).
`cross'
related to cross compilation issues.
`obsolete'
report the uses of obsolete constructs.
`portability'
portability issues
`syntax'
dubious syntactic constructs.
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
Warnings about `syntax' are enabled by default, and the environment
variable `WARNINGS', a comma separated list of categories, is
honored as well. Passing `-W CATEGORY' actually behaves as if you
had passed `--warnings=syntax,$WARNINGS,CATEGORY'. If you want to
disable the defaults and `WARNINGS', but (for example) enable the
warnings about obsolete constructs, you would use `-W
none,obsolete'.
If you want `autoreconf' to pass flags that are not listed here on
to `aclocal', set `ACLOCAL_AMFLAGS' in your `Makefile.am'.

File: autoconf.info, Node: Setup, Next: Existing Tests, Prev: Making configure Scripts, Up: Top
4 Initialization and Output Files
*********************************
Autoconf-generated `configure' scripts need some information about how
to initialize, such as how to find the package's source files and about
the output files to produce. The following sections describe the
initialization and the creation of output files.
* Menu:
* Initializing configure:: Option processing etc.
* Notices:: Copyright, version numbers in `configure'
* Input:: Where Autoconf should find files
* Output:: Outputting results from the configuration
* Configuration Actions:: Preparing the output based on results
* Configuration Files:: Creating output files
* Makefile Substitutions:: Using output variables in makefiles
* Configuration Headers:: Creating a configuration header file
* Configuration Commands:: Running arbitrary instantiation commands
* Configuration Links:: Links depending on the configuration
* Subdirectories:: Configuring independent packages together
* Default Prefix:: Changing the default installation prefix

File: autoconf.info, Node: Initializing configure, Next: Notices, Up: Setup
4.1 Initializing `configure'
============================
Every `configure' script must call `AC_INIT' before doing anything
else. The only other required macro is `AC_OUTPUT' (*note Output::).
-- Macro: AC_INIT (PACKAGE, VERSION, [BUG-REPORT], [TARNAME])
Process any command-line arguments and perform various
initializations and verifications.
Set the name of the PACKAGE and its VERSION. These are typically
used in `--version' support, including that of `configure'. The
optional argument BUG-REPORT should be the email to which users
should send bug reports. The package TARNAME differs from
PACKAGE: the latter designates the full package name (e.g., `GNU
Autoconf'), while the former is meant for distribution tar ball
names (e.g., `autoconf'). It defaults to PACKAGE with `GNU '
stripped, lower-cased, and all characters other than alphanumerics
and underscores are changed to `-'.
It is preferable that the arguments of `AC_INIT' be static, i.e.,
there should not be any shell computation, but they can be
computed by M4.
The following M4 macros (e.g., `AC_PACKAGE_NAME'), output variables
(e.g., `PACKAGE_NAME'), and preprocessor symbols (e.g.,
`PACKAGE_NAME') are defined by `AC_INIT':
`AC_PACKAGE_NAME', `PACKAGE_NAME'
Exactly PACKAGE.
`AC_PACKAGE_TARNAME', `PACKAGE_TARNAME'
Exactly TARNAME.
`AC_PACKAGE_VERSION', `PACKAGE_VERSION'
Exactly VERSION.
`AC_PACKAGE_STRING', `PACKAGE_STRING'
Exactly `PACKAGE VERSION'.
`AC_PACKAGE_BUGREPORT', `PACKAGE_BUGREPORT'
Exactly BUG-REPORT.
If your `configure' script does its own option processing, it should
inspect `$@' or `$*' immediately after calling `AC_INIT', because other
Autoconf macros liberally use the `set' command to process strings, and
this has the side effect of updating `$@' and `$*'. However, we
suggest that you use standard macros like `AC_ARG_ENABLE' instead of
attempting to implement your own option processing. *Note Site
Configuration::.

File: autoconf.info, Node: Notices, Next: Input, Prev: Initializing configure, Up: Setup
4.2 Notices in `configure'
==========================
The following macros manage version numbers for `configure' scripts.
Using them is optional.
-- Macro: AC_PREREQ (VERSION)
Ensure that a recent enough version of Autoconf is being used. If
the version of Autoconf being used to create `configure' is
earlier than VERSION, print an error message to the standard error
output and exit with failure (exit status is 63). For example:
AC_PREREQ([2.61])
This macro is the only macro that may be used before `AC_INIT', but
for consistency, you are invited not to do so.
-- Macro: AC_COPYRIGHT (COPYRIGHT-NOTICE)
State that, in addition to the Free Software Foundation's
copyright on the Autoconf macros, parts of your `configure' are
covered by the COPYRIGHT-NOTICE.
The COPYRIGHT-NOTICE shows up in both the head of `configure' and
in `configure --version'.
-- Macro: AC_REVISION (REVISION-INFO)
Copy revision stamp REVISION-INFO into the `configure' script,
with any dollar signs or double-quotes removed. This macro lets
you put a revision stamp from `configure.ac' into `configure'
without RCS or CVS changing it when you check in `configure'.
That way, you can determine easily which revision of
`configure.ac' a particular `configure' corresponds to.
For example, this line in `configure.ac':
AC_REVISION([$Revision: 1.30 $])
produces this in `configure':
#!/bin/sh
# From configure.ac Revision: 1.30

File: autoconf.info, Node: Input, Next: Output, Prev: Notices, Up: Setup
4.3 Finding `configure' Input
=============================
-- Macro: AC_CONFIG_SRCDIR (UNIQUE-FILE-IN-SOURCE-DIR)
UNIQUE-FILE-IN-SOURCE-DIR is some file that is in the package's
source directory; `configure' checks for this file's existence to
make sure that the directory that it is told contains the source
code in fact does. Occasionally people accidentally specify the
wrong directory with `--srcdir'; this is a safety check. *Note
configure Invocation::, for more information.
Packages that do manual configuration or use the `install' program
might need to tell `configure' where to find some other shell scripts
by calling `AC_CONFIG_AUX_DIR', though the default places it looks are
correct for most cases.
-- Macro: AC_CONFIG_AUX_DIR (DIR)
Use the auxiliary build tools (e.g., `install-sh', `config.sub',
`config.guess', Cygnus `configure', Automake and Libtool scripts,
etc.) that are in directory DIR. These are auxiliary files used
in configuration. DIR can be either absolute or relative to
`SRCDIR'. The default is `SRCDIR' or `SRCDIR/..' or
`SRCDIR/../..', whichever is the first that contains `install-sh'.
The other files are not checked for, so that using
`AC_PROG_INSTALL' does not automatically require distributing the
other auxiliary files. It checks for `install.sh' also, but that
name is obsolete because some `make' have a rule that creates
`install' from it if there is no makefile.
The auxiliary directory is commonly named `build-aux'. If you
need portability to DOS variants, do not name the auxiliary
directory `aux'. *Note File System Conventions::.
-- Macro: AC_REQUIRE_AUX_FILE (FILE)
Declares that FILE is expected in the directory defined above. In
Autoconf proper, this macro does nothing: its sole purpose is to be
traced by third-party tools to produce a list of expected auxiliary
files. For instance it is called by macros like `AC_PROG_INSTALL'
(*note Particular Programs::) or `AC_CANONICAL_BUILD' (*note
Canonicalizing::) to register the auxiliary files they need.
Similarly, packages that use `aclocal' should declare where local
macros can be found using `AC_CONFIG_MACRO_DIR'.
-- Macro: AC_CONFIG_MACRO_DIR (DIR)
Specify DIR as the location of additional local Autoconf macros.
This macro is intended for use by future versions of commands like
`autoreconf' that trace macro calls. It should be called directly
from `configure.ac' so that tools that install macros for
`aclocal' can find the macros' declarations.

File: autoconf.info, Node: Output, Next: Configuration Actions, Prev: Input, Up: Setup
4.4 Outputting Files
====================
Every Autoconf script, e.g., `configure.ac', should finish by calling
`AC_OUTPUT'. That is the macro that generates and runs
`config.status', which in turn creates the makefiles and any other
files resulting from configuration. This is the only required macro
besides `AC_INIT' (*note Input::).
-- Macro: AC_OUTPUT
Generate `config.status' and launch it. Call this macro once, at
the end of `configure.ac'.
`config.status' performs all the configuration actions: all the
output files (see *Note Configuration Files::, macro
`AC_CONFIG_FILES'), header files (see *Note Configuration
Headers::, macro `AC_CONFIG_HEADERS'), commands (see *Note
Configuration Commands::, macro `AC_CONFIG_COMMANDS'), links (see
*Note Configuration Links::, macro `AC_CONFIG_LINKS'),
subdirectories to configure (see *Note Subdirectories::, macro
`AC_CONFIG_SUBDIRS') are honored.
The location of your `AC_OUTPUT' invocation is the exact point
where configuration actions are taken: any code afterwards is
executed by `configure' once `config.status' was run. If you want
to bind actions to `config.status' itself (independently of
whether `configure' is being run), see *Note Running Arbitrary
Configuration Commands: Configuration Commands.
Historically, the usage of `AC_OUTPUT' was somewhat different.
*Note Obsolete Macros::, for a description of the arguments that
`AC_OUTPUT' used to support.
If you run `make' in subdirectories, you should run it using the
`make' variable `MAKE'. Most versions of `make' set `MAKE' to the name
of the `make' program plus any options it was given. (But many do not
include in it the values of any variables set on the command line, so
those are not passed on automatically.) Some old versions of `make' do
not set this variable. The following macro allows you to use it even
with those versions.
-- Macro: AC_PROG_MAKE_SET
If the Make command, `$MAKE' if set or else `make', predefines
`$(MAKE)', define output variable `SET_MAKE' to be empty.
Otherwise, define `SET_MAKE' to a macro definition that sets
`$(MAKE)', such as `MAKE=make'. Calls `AC_SUBST' for `SET_MAKE'.
If you use this macro, place a line like this in each `Makefile.in'
that runs `MAKE' on other directories:
@SET_MAKE@

File: autoconf.info, Node: Configuration Actions, Next: Configuration Files, Prev: Output, Up: Setup
4.5 Performing Configuration Actions
====================================
`configure' is designed so that it appears to do everything itself, but
there is actually a hidden slave: `config.status'. `configure' is in
charge of examining your system, but it is `config.status' that
actually takes the proper actions based on the results of `configure'.
The most typical task of `config.status' is to _instantiate_ files.
This section describes the common behavior of the four standard
instantiating macros: `AC_CONFIG_FILES', `AC_CONFIG_HEADERS',
`AC_CONFIG_COMMANDS' and `AC_CONFIG_LINKS'. They all have this
prototype:
AC_CONFIG_FOOS(TAG..., [COMMANDS], [INIT-CMDS])
where the arguments are:
TAG...
A blank-or-newline-separated list of tags, which are typically the
names of the files to instantiate.
You are encouraged to use literals as TAGS. In particular, you
should avoid
... && my_foos="$my_foos fooo"
... && my_foos="$my_foos foooo"
AC_CONFIG_FOOS([$my_foos])
and use this instead:
... && AC_CONFIG_FOOS([fooo])
... && AC_CONFIG_FOOS([foooo])
The macros `AC_CONFIG_FILES' and `AC_CONFIG_HEADERS' use special
TAG values: they may have the form `OUTPUT' or `OUTPUT:INPUTS'.
The file OUTPUT is instantiated from its templates, INPUTS
(defaulting to `OUTPUT.in').
`AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk)]', for
example, asks for the creation of the file `Makefile' that
contains the expansion of the output variables in the
concatenation of `boiler/top.mk' and `boiler/bot.mk'.
The special value `-' might be used to denote the standard output
when used in OUTPUT, or the standard input when used in the
INPUTS. You most probably don't need to use this in
`configure.ac', but it is convenient when using the command line
interface of `./config.status', see *Note config.status
Invocation::, for more details.
The INPUTS may be absolute or relative file names. In the latter
case they are first looked for in the build tree, and then in the
source tree.
COMMANDS
Shell commands output literally into `config.status', and
associated with a tag that the user can use to tell `config.status'
which the commands to run. The commands are run each time a TAG
request is given to `config.status', typically each time the file
`TAG' is created.
The variables set during the execution of `configure' are _not_
available here: you first need to set them via the INIT-CMDS.
Nonetheless the following variables are precomputed:
`srcdir'
The name of the top source directory, assuming that the
working directory is the top build directory. This is what
the `configure' option `--srcdir' sets.
`ac_top_srcdir'
The name of the top source directory, assuming that the
working directory is the current build directory.
`ac_top_build_prefix'
The name of the top build directory, assuming that the working
directory is the current build directory. It can be empty,
or else ends with a slash, so that you may concatenate it.
`ac_srcdir'
The name of the corresponding source directory, assuming that
the working directory is the current build directory.
The "current" directory refers to the directory (or
pseudo-directory) containing the input part of TAGS. For
instance, running
AC_CONFIG_COMMANDS([deep/dir/out:in/in.in], [...], [...])
with `--srcdir=../package' produces the following values:
# Argument of --srcdir
srcdir='../package'
# Reversing deep/dir
ac_top_build_prefix='../../'
# Concatenation of $ac_top_build_prefix and srcdir
ac_top_srcdir='../../../package'
# Concatenation of $ac_top_srcdir and deep/dir
ac_srcdir='../../../package/deep/dir'
independently of `in/in.in'.
INIT-CMDS
Shell commands output _unquoted_ near the beginning of
`config.status', and executed each time `config.status' runs
(regardless of the tag). Because they are unquoted, for example,
`$var' is output as the value of `var'. INIT-CMDS is typically
used by `configure' to give `config.status' some variables it
needs to run the COMMANDS.
You should be extremely cautious in your variable names: all the
INIT-CMDS share the same name space and may overwrite each other
in unpredictable ways. Sorry....
All these macros can be called multiple times, with different TAG
values, of course!

File: autoconf.info, Node: Configuration Files, Next: Makefile Substitutions, Prev: Configuration Actions, Up: Setup
4.6 Creating Configuration Files
================================
Be sure to read the previous section, *Note Configuration Actions::.
-- Macro: AC_CONFIG_FILES (FILE..., [CMDS], [INIT-CMDS])
Make `AC_OUTPUT' create each `FILE' by copying an input file (by
default `FILE.in'), substituting the output variable values. This
macro is one of the instantiating macros; see *Note Configuration
Actions::. *Note Makefile Substitutions::, for more information
on using output variables. *Note Setting Output Variables::, for
more information on creating them. This macro creates the
directory that the file is in if it doesn't exist. Usually,
makefiles are created this way, but other files, such as
`.gdbinit', can be specified as well.
Typical calls to `AC_CONFIG_FILES' look like this:
AC_CONFIG_FILES([Makefile src/Makefile man/Makefile X/Imakefile])
AC_CONFIG_FILES([autoconf], [chmod +x autoconf])
You can override an input file name by appending to FILE a
colon-separated list of input files. Examples:
AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk]
[lib/Makefile:boiler/lib.mk])
Doing this allows you to keep your file names acceptable to DOS
variants, or to prepend and/or append boilerplate to the file.

File: autoconf.info, Node: Makefile Substitutions, Next: Configuration Headers, Prev: Configuration Files, Up: Setup
4.7 Substitutions in Makefiles
==============================
Each subdirectory in a distribution that contains something to be
compiled or installed should come with a file `Makefile.in', from which
`configure' creates a file `Makefile' in that directory. To create
`Makefile', `configure' performs a simple variable substitution,
replacing occurrences of `@VARIABLE@' in `Makefile.in' with the value
that `configure' has determined for that variable. Variables that are
substituted into output files in this way are called "output
variables". They are ordinary shell variables that are set in
`configure'. To make `configure' substitute a particular variable into
the output files, the macro `AC_SUBST' must be called with that
variable name as an argument. Any occurrences of `@VARIABLE@' for
other variables are left unchanged. *Note Setting Output Variables::,
for more information on creating output variables with `AC_SUBST'.
A software package that uses a `configure' script should be
distributed with a file `Makefile.in', but no makefile; that way, the
user has to properly configure the package for the local system before
compiling it.
*Note Makefile Conventions: (standards)Makefile Conventions, for
more information on what to put in makefiles.
* Menu:
* Preset Output Variables:: Output variables that are always set
* Installation Directory Variables:: Other preset output variables
* Changed Directory Variables:: Warnings about `datarootdir'
* Build Directories:: Supporting multiple concurrent compiles
* Automatic Remaking:: Makefile rules for configuring

File: autoconf.info, Node: Preset Output Variables, Next: Installation Directory Variables, Up: Makefile Substitutions
4.7.1 Preset Output Variables
-----------------------------
Some output variables are preset by the Autoconf macros. Some of the
Autoconf macros set additional output variables, which are mentioned in
the descriptions for those macros. *Note Output Variable Index::, for a
complete list of output variables. *Note Installation Directory
Variables::, for the list of the preset ones related to installation
directories. Below are listed the other preset ones. They all are
precious variables (*note Setting Output Variables::, `AC_ARG_VAR').
-- Variable: CFLAGS
Debugging and optimization options for the C compiler. If it is
not set in the environment when `configure' runs, the default
value is set when you call `AC_PROG_CC' (or empty if you don't).
`configure' uses this variable when compiling or linking programs
to test for C features.
If a compiler option affects only the behavior of the preprocessor
(e.g., `-D NAME'), it should be put into `CPPFLAGS' instead. If
it affects only the linker (e.g., `-L DIRECTORY'), it should be
put into `LDFLAGS' instead. If it affects only the compiler
proper, `CFLAGS' is the natural home for it. If an option affects
multiple phases of the compiler, though, matters get tricky. One
approach to put such options directly into `CC', e.g., `CC='gcc
-m64''. Another is to put them into both `CPPFLAGS' and
`LDFLAGS', but not into `CFLAGS'.
-- Variable: configure_input
A comment saying that the file was generated automatically by
`configure' and giving the name of the input file. `AC_OUTPUT'
adds a comment line containing this variable to the top of every
makefile it creates. For other files, you should reference this
variable in a comment at the top of each input file. For example,
an input shell script should begin like this:
#!/bin/sh
# @configure_input@
The presence of that line also reminds people editing the file
that it needs to be processed by `configure' in order to be used.
-- Variable: CPPFLAGS
Preprocessor options for the C, C++, and Objective C preprocessors
and compilers. If it is not set in the environment when
`configure' runs, the default value is empty. `configure' uses
this variable when preprocessing or compiling programs to test for
C, C++, and Objective C features.
This variable's contents should contain options like `-I', `-D',
and `-U' that affect only the behavior of the preprocessor.
Please see the explanation of `CFLAGS' for what you can do if an
option affects other phases of the compiler as well.
Currently, `configure' always links as part of a single invocation
of the compiler that also preprocesses and compiles, so it uses
this variable also when linking programs. However, it is unwise to
depend on this behavior because the GNU coding standards do not
require it and many packages do not use `CPPFLAGS' when linking
programs.
*Note Special Chars in Variables::, for limitations that `CPPFLAGS'
might run into.
-- Variable: CXXFLAGS
Debugging and optimization options for the C++ compiler. It acts
like `CFLAGS', but for C++ instead of C.
-- Variable: DEFS
`-D' options to pass to the C compiler. If `AC_CONFIG_HEADERS' is
called, `configure' replaces `@DEFS@' with `-DHAVE_CONFIG_H'
instead (*note Configuration Headers::). This variable is not
defined while `configure' is performing its tests, only when
creating the output files. *Note Setting Output Variables::, for
how to check the results of previous tests.
-- Variable: ECHO_C
-- Variable: ECHO_N
-- Variable: ECHO_T
How does one suppress the trailing newline from `echo' for
question-answer message pairs? These variables provide a way:
echo $ECHO_N "And the winner is... $ECHO_C"
sleep 100000000000
echo "${ECHO_T}dead."
Some old and uncommon `echo' implementations offer no means to
achieve this, in which case `ECHO_T' is set to tab. You might not
want to use it.
-- Variable: ERLCFLAGS
Debugging and optimization options for the Erlang compiler. If it
is not set in the environment when `configure' runs, the default
value is empty. `configure' uses this variable when compiling
programs to test for Erlang features.
-- Variable: FCFLAGS
Debugging and optimization options for the Fortran compiler. If it
is not set in the environment when `configure' runs, the default
value is set when you call `AC_PROG_FC' (or empty if you don't).
`configure' uses this variable when compiling or linking programs
to test for Fortran features.
-- Variable: FFLAGS
Debugging and optimization options for the Fortran 77 compiler.
If it is not set in the environment when `configure' runs, the
default value is set when you call `AC_PROG_F77' (or empty if you
don't). `configure' uses this variable when compiling or linking
programs to test for Fortran 77 features.
-- Variable: LDFLAGS
Options for the linker. If it is not set in the environment when
`configure' runs, the default value is empty. `configure' uses
this variable when linking programs to test for C, C++, Objective
C, and Fortran features.
This variable's contents should contain options like `-s' and `-L'
that affect only the behavior of the linker. Please see the
explanation of `CFLAGS' for what you can do if an option also
affects other phases of the compiler.
Don't use this variable to pass library names (`-l') to the
linker; use `LIBS' instead.
-- Variable: LIBS
`-l' options to pass to the linker. The default value is empty,
but some Autoconf macros may prepend extra libraries to this
variable if those libraries are found and provide necessary
functions, see *Note Libraries::. `configure' uses this variable
when linking programs to test for C, C++, and Fortran features.
-- Variable: OBJCFLAGS
Debugging and optimization options for the Objective C compiler.
It acts like `CFLAGS', but for Objective C instead of C.
-- Variable: builddir
Rigorously equal to `.'. Added for symmetry only.
-- Variable: abs_builddir
Absolute name of `builddir'.
-- Variable: top_builddir
The relative name of the top level of the current build tree. In
the top-level directory, this is the same as `builddir'.
-- Variable: abs_top_builddir
Absolute name of `top_builddir'.
-- Variable: srcdir
The name of the directory that contains the source code for that
makefile.
-- Variable: abs_srcdir
Absolute name of `srcdir'.
-- Variable: top_srcdir
The name of the top-level source code directory for the package.
In the top-level directory, this is the same as `srcdir'.
-- Variable: abs_top_srcdir
Absolute name of `top_srcdir'.

File: autoconf.info, Node: Installation Directory Variables, Next: Changed Directory Variables, Prev: Preset Output Variables, Up: Makefile Substitutions
4.7.2 Installation Directory Variables
--------------------------------------
The following variables specify the directories for package
installation, see *Note Variables for Installation Directories:
(standards)Directory Variables, for more information. See the end of
this section for details on when and how to use these variables.
-- Variable: bindir
The directory for installing executables that users run.
-- Variable: datadir
The directory for installing idiosyncratic read-only
architecture-independent data.
-- Variable: datarootdir
The root of the directory tree for read-only
architecture-independent data files.
-- Variable: docdir
The directory for installing documentation files (other than Info
and man).
-- Variable: dvidir
The directory for installing documentation files in DVI format.
-- Variable: exec_prefix
The installation prefix for architecture-dependent files. By
default it's the same as PREFIX. You should avoid installing
anything directly to EXEC_PREFIX. However, the default value for
directories containing architecture-dependent files should be
relative to EXEC_PREFIX.
-- Variable: htmldir
The directory for installing HTML documentation.
-- Variable: includedir
The directory for installing C header files.
-- Variable: infodir
The directory for installing documentation in Info format.
-- Variable: libdir
The directory for installing object code libraries.
-- Variable: libexecdir
The directory for installing executables that other programs run.
-- Variable: localedir
The directory for installing locale-dependent but
architecture-independent data, such as message catalogs. This
directory usually has a subdirectory per locale.
-- Variable: localstatedir
The directory for installing modifiable single-machine data.
-- Variable: mandir
The top-level directory for installing documentation in man format.
-- Variable: oldincludedir
The directory for installing C header files for non-GCC compilers.
-- Variable: pdfdir
The directory for installing PDF documentation.
-- Variable: prefix
The common installation prefix for all files. If EXEC_PREFIX is
defined to a different value, PREFIX is used only for
architecture-independent files.
-- Variable: psdir
The directory for installing PostScript documentation.
-- Variable: sbindir
The directory for installing executables that system
administrators run.
-- Variable: sharedstatedir
The directory for installing modifiable architecture-independent
data.
-- Variable: sysconfdir
The directory for installing read-only single-machine data.
Most of these variables have values that rely on `prefix' or
`exec_prefix'. It is deliberate that the directory output variables
keep them unexpanded: typically `@datarootdir@' is replaced by
`${prefix}/share', not `/usr/local/share', and `@datadir@' is replaced
by `${datarootdir}'.
This behavior is mandated by the GNU coding standards, so that when
the user runs:
`make'
she can still specify a different prefix from the one specified to
`configure', in which case, if needed, the package should hard
code dependencies corresponding to the make-specified prefix.
`make install'
she can specify a different installation location, in which case
the package _must_ still depend on the location which was compiled
in (i.e., never recompile when `make install' is run). This is an
extremely important feature, as many people may decide to install
all the files of a package grouped together, and then install
links from the final locations to there.
In order to support these features, it is essential that
`datarootdir' remains being defined as `${prefix}/share' to depend upon
the current value of `prefix'.
A corollary is that you should not use these variables except in
makefiles. For instance, instead of trying to evaluate `datadir' in
`configure' and hard-coding it in makefiles using e.g.,
`AC_DEFINE_UNQUOTED([DATADIR], ["$datadir"], [Data directory.])', you
should add `-DDATADIR='$(datadir)'' to your makefile's definition of
`CPPFLAGS' (`AM_CPPFLAGS' if you are also using Automake).
Similarly, you should not rely on `AC_CONFIG_FILES' to replace
`datadir' and friends in your shell scripts and other files; instead,
let `make' manage their replacement. For instance Autoconf ships
templates of its shell scripts ending with `.in', and uses a makefile
snippet similar to the following to build scripts like `autoheader' and
`autom4te':
edit = sed \
-e 's|@datadir[@]|$(pkgdatadir)|g' \
-e 's|@prefix[@]|$(prefix)|g'
autoheader autom4te: Makefile
rm -f $@ $@.tmp
$(edit) '$(srcdir)/$@.in' >$@.tmp
chmod +x $@.tmp
chmod a-w $@.tmp
mv $@.tmp $@
autoheader: $(srcdir)/autoheader.in
autom4te: $(srcdir)/autom4te.in
Some details are noteworthy:
`@datadir[@]'
The brackets prevent `configure' from replacing `@datadir@' in the
Sed expression itself. Brackets are preferable to a backslash
here, since Posix says `\@' is not portable.
`$(pkgdatadir)'
Don't use `@pkgdatadir@'! Use the matching makefile variable
instead.
`/'
Don't use `/' in the Sed expressions that replace file names since
most likely the variables you use, such as `$(pkgdatadir)',
contain `/'. Use a shell metacharacter instead, such as `|'.
special characters
File names, file name components, and the value of `VPATH' should
not contain shell metacharacters or white space. *Note Special
Chars in Variables::.
dependency on `Makefile'
Since `edit' uses values that depend on the configuration specific
values (`prefix', etc.) and not only on `VERSION' and so forth,
the output depends on `Makefile', not `configure.ac'.
`$@'
The main rule is generic, and uses `$@' extensively to avoid the
need for multiple copies of the rule.
Separated dependencies and single suffix rules
You can't use them! The above snippet cannot be (portably)
rewritten as:
autoconf autoheader: Makefile
.in:
rm -f $@ $@.tmp
$(edit) $< >$@.tmp
chmod +x $@.tmp
mv $@.tmp $@
*Note Single Suffix Rules::, for details.
`$(srcdir)'
Be sure to specify the name of the source directory, otherwise the
package won't support separated builds.
For the more specific installation of Erlang libraries, the
following variables are defined:
-- Variable: ERLANG_INSTALL_LIB_DIR
The common parent directory of Erlang library installation
directories. This variable is set by calling the
`AC_ERLANG_SUBST_INSTALL_LIB_DIR' macro in `configure.ac'.
-- Variable: ERLANG_INSTALL_LIB_DIR_LIBRARY
The installation directory for Erlang library LIBRARY. This
variable is set by calling the
`AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR(LIBRARY, VERSION' macro in
`configure.ac'.
*Note Erlang Libraries::, for details.

File: autoconf.info, Node: Changed Directory Variables, Next: Build Directories, Prev: Installation Directory Variables, Up: Makefile Substitutions
4.7.3 Changed Directory Variables
---------------------------------
In Autoconf 2.60, the set of directory variables has changed, and the
defaults of some variables have been adjusted (*note Installation
Directory Variables::) to changes in the GNU Coding Standards.
Notably, `datadir', `infodir', and `mandir' are now expressed in terms
of `datarootdir'. If you are upgrading from an earlier Autoconf
version, you may need to adjust your files to ensure that the directory
variables are substituted correctly (*note Defining Directories::), and
that a definition of `datarootdir' is in place. For example, in a
`Makefile.in', adding
datarootdir = @datarootdir@
is usually sufficient. If you use Automake to create `Makefile.in', it
will add this for you.
To help with the transition, Autoconf warns about files that seem to
use `datarootdir' without defining it. In some cases, it then expands
the value of `$datarootdir' in substitutions of the directory
variables. The following example shows such a warning:
$ cat configure.ac
AC_INIT
AC_CONFIG_FILES([Makefile])
AC_OUTPUT
$ cat Makefile.in
prefix = @prefix@
datadir = @datadir@
$ autoconf
$ configure
configure: creating ./config.status
config.status: creating Makefile
config.status: WARNING:
Makefile.in seems to ignore the --datarootdir setting
$ cat Makefile
prefix = /usr/local
datadir = ${prefix}/share
Usually one can easily change the file to accommodate both older and
newer Autoconf releases:
$ cat Makefile.in
prefix = @prefix@
datarootdir = @datarootdir@
datadir = @datadir@
$ configure
configure: creating ./config.status
config.status: creating Makefile
$ cat Makefile
prefix = /usr/local
datarootdir = ${prefix}/share
datadir = ${datarootdir}
In some cases, however, the checks may not be able to detect that a
suitable initialization of `datarootdir' is in place, or they may fail
to detect that such an initialization is necessary in the output file.
If, after auditing your package, there are still spurious `configure'
warnings about `datarootdir', you may add the line
AC_DEFUN([AC_DATAROOTDIR_CHECKED])
to your `configure.ac' to disable the warnings. This is an exception
to the usual rule that you should not define a macro whose name begins
with `AC_' (*note Macro Names::).

File: autoconf.info, Node: Build Directories, Next: Automatic Remaking, Prev: Changed Directory Variables, Up: Makefile Substitutions
4.7.4 Build Directories
-----------------------
You can support compiling a software package for several architectures
simultaneously from the same copy of the source code. The object files
for each architecture are kept in their own directory.
To support doing this, `make' uses the `VPATH' variable to find the
files that are in the source directory. GNU Make and most other recent
`make' programs can do this. Older `make' programs do not support
`VPATH'; when using them, the source code must be in the same directory
as the object files.
To support `VPATH', each `Makefile.in' should contain two lines that
look like:
srcdir = @srcdir@
VPATH = @srcdir@
Do not set `VPATH' to the value of another variable, for example
`VPATH = $(srcdir)', because some versions of `make' do not do variable
substitutions on the value of `VPATH'.
`configure' substitutes the correct value for `srcdir' when it
produces `Makefile'.
Do not use the `make' variable `$<', which expands to the file name
of the file in the source directory (found with `VPATH'), except in
implicit rules. (An implicit rule is one such as `.c.o', which tells
how to create a `.o' file from a `.c' file.) Some versions of `make'
do not set `$<' in explicit rules; they expand it to an empty value.
Instead, Make command lines should always refer to source files by
prefixing them with `$(srcdir)/'. For example:
time.info: time.texinfo
$(MAKEINFO) '$(srcdir)/time.texinfo'

File: autoconf.info, Node: Automatic Remaking, Prev: Build Directories, Up: Makefile Substitutions
4.7.5 Automatic Remaking
------------------------
You can put rules like the following in the top-level `Makefile.in' for
a package to automatically update the configuration information when
you change the configuration files. This example includes all of the
optional files, such as `aclocal.m4' and those related to configuration
header files. Omit from the `Makefile.in' rules for any of these files
that your package does not use.
The `$(srcdir)/' prefix is included because of limitations in the
`VPATH' mechanism.
The `stamp-' files are necessary because the timestamps of
`config.h.in' and `config.h' are not changed if remaking them does not
change their contents. This feature avoids unnecessary recompilation.
You should include the file `stamp-h.in' your package's distribution,
so that `make' considers `config.h.in' up to date. Don't use `touch'
(*note Limitations of Usual Tools::); instead, use `echo' (using `date'
would cause needless differences, hence CVS conflicts, etc.).
$(srcdir)/configure: configure.ac aclocal.m4
cd '$(srcdir)' && autoconf
# autoheader might not change config.h.in, so touch a stamp file.
$(srcdir)/config.h.in: stamp-h.in
$(srcdir)/stamp-h.in: configure.ac aclocal.m4
cd '$(srcdir)' && autoheader
echo timestamp > '$(srcdir)/stamp-h.in'
config.h: stamp-h
stamp-h: config.h.in config.status
./config.status
Makefile: Makefile.in config.status
./config.status
config.status: configure
./config.status --recheck
(Be careful if you copy these lines directly into your makefile, as you
need to convert the indented lines to start with the tab character.)
In addition, you should use
AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h])
so `config.status' ensures that `config.h' is considered up to date.
*Note Output::, for more information about `AC_OUTPUT'.
*Note config.status Invocation::, for more examples of handling
configuration-related dependencies.

File: autoconf.info, Node: Configuration Headers, Next: Configuration Commands, Prev: Makefile Substitutions, Up: Setup
4.8 Configuration Header Files
==============================
When a package contains more than a few tests that define C preprocessor
symbols, the command lines to pass `-D' options to the compiler can get
quite long. This causes two problems. One is that the `make' output
is hard to visually scan for errors. More seriously, the command lines
can exceed the length limits of some operating systems. As an
alternative to passing `-D' options to the compiler, `configure'
scripts can create a C header file containing `#define' directives.
The `AC_CONFIG_HEADERS' macro selects this kind of output. Though it
can be called anywhere between `AC_INIT' and `AC_OUTPUT', it is
customary to call it right after `AC_INIT'.
The package should `#include' the configuration header file before
any other header files, to prevent inconsistencies in declarations (for
example, if it redefines `const').
To provide for VPATH builds, remember to pass the C compiler a `-I.'
option (or `-I..'; whichever directory contains `config.h'). Even if
you use `#include "config.h"', the preprocessor searches only the
directory of the currently read file, i.e., the source directory, not
the build directory.
With the appropriate `-I' option, you can use `#include <config.h>'.
Actually, it's a good habit to use it, because in the rare case when
the source directory contains another `config.h', the build directory
should be searched first.
-- Macro: AC_CONFIG_HEADERS (HEADER ..., [CMDS], [INIT-CMDS])
This macro is one of the instantiating macros; see *Note
Configuration Actions::. Make `AC_OUTPUT' create the file(s) in
the blank-or-newline-separated list HEADER containing C
preprocessor `#define' statements, and replace `@DEFS@' in
generated files with `-DHAVE_CONFIG_H' instead of the value of
`DEFS'. The usual name for HEADER is `config.h'.
If HEADER already exists and its contents are identical to what
`AC_OUTPUT' would put in it, it is left alone. Doing this allows
making some changes in the configuration without needlessly causing
object files that depend on the header file to be recompiled.
Usually the input file is named `HEADER.in'; however, you can
override the input file name by appending to HEADER a
colon-separated list of input files. Examples:
AC_CONFIG_HEADERS([config.h:config.hin])
AC_CONFIG_HEADERS([defines.h:defs.pre:defines.h.in:defs.post])
Doing this allows you to keep your file names acceptable to DOS
variants, or to prepend and/or append boilerplate to the file.
-- Macro: AH_HEADER
This macro is defined as the name of the first declared config
header and undefined if no config headers have been declared up to
this point. A third-party macro may, for example, require use of
a config header without invoking AC_CONFIG_HEADERS twice, like
this:
AC_CONFIG_COMMANDS_PRE(
[m4_ifndef([AH_HEADER], [AC_CONFIG_HEADERS([config.h])])])
*Note Configuration Actions::, for more details on HEADER.
* Menu:
* Header Templates:: Input for the configuration headers
* autoheader Invocation:: How to create configuration templates
* Autoheader Macros:: How to specify CPP templates

File: autoconf.info, Node: Header Templates, Next: autoheader Invocation, Up: Configuration Headers
4.8.1 Configuration Header Templates
------------------------------------
Your distribution should contain a template file that looks as you want
the final header file to look, including comments, with `#undef'
statements which are used as hooks. For example, suppose your
`configure.ac' makes these calls:
AC_CONFIG_HEADERS([conf.h])
AC_CHECK_HEADERS([unistd.h])
Then you could have code like the following in `conf.h.in'. On systems
that have `unistd.h', `configure' defines `HAVE_UNISTD_H' to 1. On
other systems, the whole line is commented out (in case the system
predefines that symbol).
/* Define as 1 if you have unistd.h. */
#undef HAVE_UNISTD_H
Pay attention that `#undef' is in the first column, and there is
nothing after `HAVE_UNISTD_H', not even white space. You can then
decode the configuration header using the preprocessor directives:
#include <conf.h>
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#else
/* We are in trouble. */
#endif
The use of old form templates, with `#define' instead of `#undef' is
strongly discouraged. Similarly with old templates with comments on
the same line as the `#undef'. Anyway, putting comments in
preprocessor macros has never been a good idea.
Since it is a tedious task to keep a template header up to date, you
may use `autoheader' to generate it, see *Note autoheader Invocation::.

File: autoconf.info, Node: autoheader Invocation, Next: Autoheader Macros, Prev: Header Templates, Up: Configuration Headers
4.8.2 Using `autoheader' to Create `config.h.in'
------------------------------------------------
The `autoheader' program can create a template file of C `#define'
statements for `configure' to use. If `configure.ac' invokes
`AC_CONFIG_HEADERS(FILE)', `autoheader' creates `FILE.in'; if multiple
file arguments are given, the first one is used. Otherwise,
`autoheader' creates `config.h.in'.
In order to do its job, `autoheader' needs you to document all of
the symbols that you might use. Typically this is done via an
`AC_DEFINE' or `AC_DEFINE_UNQUOTED' call whose first argument is a
literal symbol and whose third argument describes the symbol (*note
Defining Symbols::). Alternatively, you can use `AH_TEMPLATE' (*note
Autoheader Macros::), or you can supply a suitable input file for a
subsequent configuration header file. Symbols defined by Autoconf's
builtin tests are already documented properly; you need to document
only those that you define yourself.
You might wonder why `autoheader' is needed: after all, why would
`configure' need to "patch" a `config.h.in' to produce a `config.h'
instead of just creating `config.h' from scratch? Well, when
everything rocks, the answer is just that we are wasting our time
maintaining `autoheader': generating `config.h' directly is all that is
needed. When things go wrong, however, you'll be thankful for the
existence of `autoheader'.
The fact that the symbols are documented is important in order to
_check_ that `config.h' makes sense. The fact that there is a
well-defined list of symbols that should be defined (or not) is also
important for people who are porting packages to environments where
`configure' cannot be run: they just have to _fill in the blanks_.
But let's come back to the point: the invocation of `autoheader'...
If you give `autoheader' an argument, it uses that file instead of
`configure.ac' and writes the header file to the standard output
instead of to `config.h.in'. If you give `autoheader' an argument of
`-', it reads the standard input instead of `configure.ac' and writes
the header file to the standard output.
`autoheader' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Remake the template file even if newer than its input files.
`--include=DIR'
`-I DIR'
Append DIR to the include path. Multiple invocations accumulate.
`--prepend-include=DIR'
`-B DIR'
Prepend DIR to the include path. Multiple invocations accumulate.
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list). Current categories include:
`obsolete'
report the uses of obsolete constructs
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY

File: autoconf.info, Node: Autoheader Macros, Prev: autoheader Invocation, Up: Configuration Headers
4.8.3 Autoheader Macros
-----------------------
`autoheader' scans `configure.ac' and figures out which C preprocessor
symbols it might define. It knows how to generate templates for
symbols defined by `AC_CHECK_HEADERS', `AC_CHECK_FUNCS' etc., but if
you `AC_DEFINE' any additional symbol, you must define a template for
it. If there are missing templates, `autoheader' fails with an error
message.
The template for a SYMBOL is created by `autoheader' from the
DESCRIPTION argument to an `AC_DEFINE'; see *Note Defining Symbols::.
For special needs, you can use the following macros.
-- Macro: AH_TEMPLATE (KEY, DESCRIPTION)
Tell `autoheader' to generate a template for KEY. This macro
generates standard templates just like `AC_DEFINE' when a
DESCRIPTION is given.
For example:
AH_TEMPLATE([CRAY_STACKSEG_END],
[Define to one of _getb67, GETB67, getb67
for Cray-2 and Cray-YMP systems. This
function is required for alloca.c support
on those systems.])
generates the following template, with the description properly
justified.
/* Define to one of _getb67, GETB67, getb67 for Cray-2 and
Cray-YMP systems. This function is required for alloca.c
support on those systems. */
#undef CRAY_STACKSEG_END
-- Macro: AH_VERBATIM (KEY, TEMPLATE)
Tell `autoheader' to include the TEMPLATE as-is in the header
template file. This TEMPLATE is associated with the KEY, which is
used to sort all the different templates and guarantee their
uniqueness. It should be a symbol that can be defined via
`AC_DEFINE'.
-- Macro: AH_TOP (TEXT)
Include TEXT at the top of the header template file.
-- Macro: AH_BOTTOM (TEXT)
Include TEXT at the bottom of the header template file.
Please note that TEXT gets included "verbatim" to the template file,
not to the resulting config header, so it can easily get mangled when
the template is processed. There is rarely a need for something other
than
AH_BOTTOM([#include <custom.h>])

File: autoconf.info, Node: Configuration Commands, Next: Configuration Links, Prev: Configuration Headers, Up: Setup
4.9 Running Arbitrary Configuration Commands
============================================
You can execute arbitrary commands before, during, and after
`config.status' is run. The three following macros accumulate the
commands to run when they are called multiple times.
`AC_CONFIG_COMMANDS' replaces the obsolete macro `AC_OUTPUT_COMMANDS';
see *Note Obsolete Macros::, for details.
-- Macro: AC_CONFIG_COMMANDS (TAG..., [CMDS], [INIT-CMDS])
Specify additional shell commands to run at the end of
`config.status', and shell commands to initialize any variables
from `configure'. Associate the commands with TAG. Since
typically the CMDS create a file, TAG should naturally be the name
of that file. If needed, the directory hosting TAG is created.
This macro is one of the instantiating macros; see *Note
Configuration Actions::.
Here is an unrealistic example:
fubar=42
AC_CONFIG_COMMANDS([fubar],
[echo this is extra $fubar, and so on.],
[fubar=$fubar])
Here is a better one:
AC_CONFIG_COMMANDS([timestamp], [date >timestamp])
The following two macros look similar, but in fact they are not of
the same breed: they are executed directly by `configure', so you
cannot use `config.status' to rerun them.
-- Macro: AC_CONFIG_COMMANDS_PRE (CMDS)
Execute the CMDS right before creating `config.status'.
This macro presents the last opportunity to call `AC_SUBST',
`AC_DEFINE', or `AC_CONFIG_FOOS' macros.
-- Macro: AC_CONFIG_COMMANDS_POST (CMDS)
Execute the CMDS right after creating `config.status'.

File: autoconf.info, Node: Configuration Links, Next: Subdirectories, Prev: Configuration Commands, Up: Setup
4.10 Creating Configuration Links
=================================
You may find it convenient to create links whose destinations depend
upon results of tests. One can use `AC_CONFIG_COMMANDS' but the
creation of relative symbolic links can be delicate when the package is
built in a directory different from the source directory.
-- Macro: AC_CONFIG_LINKS (DEST:SOURCE..., [CMDS], [INIT-CMDS])
Make `AC_OUTPUT' link each of the existing files SOURCE to the
corresponding link name DEST. Makes a symbolic link if possible,
otherwise a hard link if possible, otherwise a copy. The DEST and
SOURCE names should be relative to the top level source or build
directory. This macro is one of the instantiating macros; see
*Note Configuration Actions::.
For example, this call:
AC_CONFIG_LINKS([host.h:config/$machine.h
object.h:config/$obj_format.h])
creates in the current directory `host.h' as a link to
`SRCDIR/config/$machine.h', and `object.h' as a link to
`SRCDIR/config/$obj_format.h'.
The tempting value `.' for DEST is invalid: it makes it impossible
for `config.status' to guess the links to establish.
One can then run:
./config.status host.h object.h
to create the links.

File: autoconf.info, Node: Subdirectories, Next: Default Prefix, Prev: Configuration Links, Up: Setup
4.11 Configuring Other Packages in Subdirectories
=================================================
In most situations, calling `AC_OUTPUT' is sufficient to produce
makefiles in subdirectories. However, `configure' scripts that control
more than one independent package can use `AC_CONFIG_SUBDIRS' to run
`configure' scripts for other packages in subdirectories.
-- Macro: AC_CONFIG_SUBDIRS (DIR ...)
Make `AC_OUTPUT' run `configure' in each subdirectory DIR in the
given blank-or-newline-separated list. Each DIR should be a
literal, i.e., please do not use:
if test "$package_foo_enabled" = yes; then
$my_subdirs="$my_subdirs foo"
fi
AC_CONFIG_SUBDIRS([$my_subdirs])
because this prevents `./configure --help=recursive' from
displaying the options of the package `foo'. Instead, you should
write:
if test "$package_foo_enabled" = yes; then
AC_CONFIG_SUBDIRS([foo])
fi
If a given DIR is not found, an error is reported: if the
subdirectory is optional, write:
if test -d "$srcdir/foo"; then
AC_CONFIG_SUBDIRS([foo])
fi
If a given DIR contains `configure.gnu', it is run instead of
`configure'. This is for packages that might use a non-Autoconf
script `Configure', which can't be called through a wrapper
`configure' since it would be the same file on case-insensitive
file systems. Likewise, if a DIR contains `configure.in' but no
`configure', the Cygnus `configure' script found by
`AC_CONFIG_AUX_DIR' is used.
The subdirectory `configure' scripts are given the same command
line options that were given to this `configure' script, with minor
changes if needed, which include:
- adjusting a relative name for the cache file;
- adjusting a relative name for the source directory;
- propagating the current value of `$prefix', including if it
was defaulted, and if the default values of the top level and
of the subdirectory `configure' differ.
This macro also sets the output variable `subdirs' to the list of
directories `DIR ...'. Make rules can use this variable to
determine which subdirectories to recurse into.
This macro may be called multiple times.

File: autoconf.info, Node: Default Prefix, Prev: Subdirectories, Up: Setup
4.12 Default Prefix
===================
By default, `configure' sets the prefix for files it installs to
`/usr/local'. The user of `configure' can select a different prefix
using the `--prefix' and `--exec-prefix' options. There are two ways
to change the default: when creating `configure', and when running it.
Some software packages might want to install in a directory other
than `/usr/local' by default. To accomplish that, use the
`AC_PREFIX_DEFAULT' macro.
-- Macro: AC_PREFIX_DEFAULT (PREFIX)
Set the default installation prefix to PREFIX instead of
`/usr/local'.
It may be convenient for users to have `configure' guess the
installation prefix from the location of a related program that they
have already installed. If you wish to do that, you can call
`AC_PREFIX_PROGRAM'.
-- Macro: AC_PREFIX_PROGRAM (PROGRAM)
If the user did not specify an installation prefix (using the
`--prefix' option), guess a value for it by looking for PROGRAM in
`PATH', the way the shell does. If PROGRAM is found, set the
prefix to the parent of the directory containing PROGRAM, else
default the prefix as described above (`/usr/local' or
`AC_PREFIX_DEFAULT'). For example, if PROGRAM is `gcc' and the
`PATH' contains `/usr/local/gnu/bin/gcc', set the prefix to
`/usr/local/gnu'.

File: autoconf.info, Node: Existing Tests, Next: Writing Tests, Prev: Setup, Up: Top
5 Existing Tests
****************
These macros test for particular system features that packages might
need or want to use. If you need to test for a kind of feature that
none of these macros check for, you can probably do it by calling
primitive test macros with appropriate arguments (*note Writing
Tests::).
These tests print messages telling the user which feature they're
checking for, and what they find. They cache their results for future
`configure' runs (*note Caching Results::).
Some of these macros set output variables. *Note Makefile
Substitutions::, for how to get their values. The phrase "define NAME"
is used below as a shorthand to mean "define the C preprocessor symbol
NAME to the value 1". *Note Defining Symbols::, for how to get those
symbol definitions into your program.
* Menu:
* Common Behavior:: Macros' standard schemes
* Alternative Programs:: Selecting between alternative programs
* Files:: Checking for the existence of files
* Libraries:: Library archives that might be missing
* Library Functions:: C library functions that might be missing
* Header Files:: Header files that might be missing
* Declarations:: Declarations that may be missing
* Structures:: Structures or members that might be missing
* Types:: Types that might be missing
* Compilers and Preprocessors:: Checking for compiling programs
* System Services:: Operating system services
* Posix Variants:: Special kludges for specific Posix variants
* Erlang Libraries:: Checking for the existence of Erlang libraries

File: autoconf.info, Node: Common Behavior, Next: Alternative Programs, Up: Existing Tests
5.1 Common Behavior
===================
Much effort has been expended to make Autoconf easy to learn. The most
obvious way to reach this goal is simply to enforce standard interfaces
and behaviors, avoiding exceptions as much as possible. Because of
history and inertia, unfortunately, there are still too many exceptions
in Autoconf; nevertheless, this section describes some of the common
rules.
* Menu:
* Standard Symbols:: Symbols defined by the macros
* Default Includes:: Includes used by the generic macros

File: autoconf.info, Node: Standard Symbols, Next: Default Includes, Up: Common Behavior
5.1.1 Standard Symbols
----------------------
All the generic macros that `AC_DEFINE' a symbol as a result of their
test transform their ARGUMENT values to a standard alphabet. First,
ARGUMENT is converted to upper case and any asterisks (`*') are each
converted to `P'. Any remaining characters that are not alphanumeric
are converted to underscores.
For instance,
AC_CHECK_TYPES([struct $Expensive*])
defines the symbol `HAVE_STRUCT__EXPENSIVEP' if the check succeeds.

File: autoconf.info, Node: Default Includes, Prev: Standard Symbols, Up: Common Behavior
5.1.2 Default Includes
----------------------
Several tests depend upon a set of header files. Since these headers
are not universally available, tests actually have to provide a set of
protected includes, such as:
#ifdef TIME_WITH_SYS_TIME
# include <sys/time.h>
# include <time.h>
#else
# ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
# else
# include <time.h>
# endif
#endif
Unless you know exactly what you are doing, you should avoid using
unconditional includes, and check the existence of the headers you
include beforehand (*note Header Files::).
Most generic macros use the following macro to provide the default
set of includes:
-- Macro: AC_INCLUDES_DEFAULT ([INCLUDE-DIRECTIVES])
Expand to INCLUDE-DIRECTIVES if defined, otherwise to:
#include <stdio.h>
#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif
#ifdef HAVE_SYS_STAT_H
# include <sys/stat.h>
#endif
#ifdef STDC_HEADERS
# include <stdlib.h>
# include <stddef.h>
#else
# ifdef HAVE_STDLIB_H
# include <stdlib.h>
# endif
#endif
#ifdef HAVE_STRING_H
# if !defined STDC_HEADERS && defined HAVE_MEMORY_H
# include <memory.h>
# endif
# include <string.h>
#endif
#ifdef HAVE_STRINGS_H
# include <strings.h>
#endif
#ifdef HAVE_INTTYPES_H
# include <inttypes.h>
#endif
#ifdef HAVE_STDINT_H
# include <stdint.h>
#endif
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif
If the default includes are used, then check for the presence of
these headers and their compatibility, i.e., you don't need to run
`AC_HEADER_STDC', nor check for `stdlib.h' etc.
These headers are checked for in the same order as they are
included. For instance, on some systems `string.h' and
`strings.h' both exist, but conflict. Then `HAVE_STRING_H' is
defined, not `HAVE_STRINGS_H'.

File: autoconf.info, Node: Alternative Programs, Next: Files, Prev: Common Behavior, Up: Existing Tests
5.2 Alternative Programs
========================
These macros check for the presence or behavior of particular programs.
They are used to choose between several alternative programs and to
decide what to do once one has been chosen. If there is no macro
specifically defined to check for a program you need, and you don't need
to check for any special properties of it, then you can use one of the
general program-check macros.
* Menu:
* Particular Programs:: Special handling to find certain programs
* Generic Programs:: How to find other programs

File: autoconf.info, Node: Particular Programs, Next: Generic Programs, Up: Alternative Programs
5.2.1 Particular Program Checks
-------------------------------
These macros check for particular programs--whether they exist, and in
some cases whether they support certain features.
-- Macro: AC_PROG_AWK
Check for `gawk', `mawk', `nawk', and `awk', in that order, and
set output variable `AWK' to the first one that is found. It
tries `gawk' first because that is reported to be the best
implementation.
-- Macro: AC_PROG_GREP
Look for the best available `grep' or `ggrep' that accepts the
longest input lines possible, and that supports multiple `-e'
options. Set the output variable `GREP' to whatever is chosen.
*Note Limitations of Usual Tools::, for more information about
portability problems with the `grep' command family.
-- Macro: AC_PROG_EGREP
Check whether `$GREP -E' works, or else look for the best available
`egrep' or `gegrep' that accepts the longest input lines possible.
Set the output variable `EGREP' to whatever is chosen.
-- Macro: AC_PROG_FGREP
Check whether `$GREP -F' works, or else look for the best available
`fgrep' or `gfgrep' that accepts the longest input lines possible.
Set the output variable `FGREP' to whatever is chosen.
-- Macro: AC_PROG_INSTALL
Set output variable `INSTALL' to the name of a BSD-compatible
`install' program, if one is found in the current `PATH'.
Otherwise, set `INSTALL' to `DIR/install-sh -c', checking the
directories specified to `AC_CONFIG_AUX_DIR' (or its default
directories) to determine DIR (*note Output::). Also set the
variables `INSTALL_PROGRAM' and `INSTALL_SCRIPT' to `${INSTALL}'
and `INSTALL_DATA' to `${INSTALL} -m 644'.
`@INSTALL@' is special, as its value may vary for different
configuration files.
This macro screens out various instances of `install' known not to
work. It prefers to find a C program rather than a shell script,
for speed. Instead of `install-sh', it can also use `install.sh',
but that name is obsolete because some `make' programs have a rule
that creates `install' from it if there is no makefile.
Autoconf comes with a copy of `install-sh' that you can use. If
you use `AC_PROG_INSTALL', you must include either `install-sh' or
`install.sh' in your distribution; otherwise `configure' produces
an error message saying it can't find them--even if the system
you're on has a good `install' program. This check is a safety
measure to prevent you from accidentally leaving that file out,
which would prevent your package from installing on systems that
don't have a BSD-compatible `install' program.
If you need to use your own installation program because it has
features not found in standard `install' programs, there is no
reason to use `AC_PROG_INSTALL'; just put the file name of your
program into your `Makefile.in' files.
-- Macro: AC_PROG_MKDIR_P
Set output variable `MKDIR_P' to a program that ensures that for
each argument, a directory named by this argument exists, creating
it and its parent directories if needed, and without race
conditions when two instances of the program attempt to make the
same directory at nearly the same time.
This macro uses the `mkdir -p' command if possible. Otherwise, it
falls back on invoking `install-sh' with the `-d' option, so your
package should contain `install-sh' as described under
`AC_PROG_INSTALL'. An `install-sh' file that predates Autoconf
2.60 or Automake 1.10 is vulnerable to race conditions, so if you
want to support parallel installs from different packages into the
same directory you need to make sure you have an up-to-date
`install-sh'. In particular, be careful about using `autoreconf
-if' if your Automake predates Automake 1.10.
This macro is related to the `AS_MKDIR_P' macro (*note Programming
in M4sh::), but it sets an output variable intended for use in
other files, whereas `AS_MKDIR_P' is intended for use in scripts
like `configure'. Also, `AS_MKDIR_P' does not accept options, but
`MKDIR_P' supports the `-m' option, e.g., a makefile might invoke
`$(MKDIR_P) -m 0 dir' to create an inaccessible directory, and
conversely a makefile should use `$(MKDIR_P) -- $(FOO)' if FOO
might yield a value that begins with `-'. Finally, `AS_MKDIR_P'
does not check for race condition vulnerability, whereas
`AC_PROG_MKDIR_P' does.
`@MKDIR_P@' is special, as its value may vary for different
configuration files.
-- Macro: AC_PROG_LEX
If `flex' is found, set output variable `LEX' to `flex' and
`LEXLIB' to `-lfl', if that library is in a standard place.
Otherwise set `LEX' to `lex' and `LEXLIB' to `-ll'.
Define `YYTEXT_POINTER' if `yytext' defaults to `char *' instead
of to `char []'. Also set output variable `LEX_OUTPUT_ROOT' to
the base of the file name that the lexer generates; usually
`lex.yy', but sometimes something else. These results vary
according to whether `lex' or `flex' is being used.
You are encouraged to use Flex in your sources, since it is both
more pleasant to use than plain Lex and the C source it produces
is portable. In order to ensure portability, however, you must
either provide a function `yywrap' or, if you don't use it (e.g.,
your scanner has no `#include'-like feature), simply include a
`%noyywrap' statement in the scanner's source. Once this done,
the scanner is portable (unless _you_ felt free to use nonportable
constructs) and does not depend on any library. In this case, and
in this case only, it is suggested that you use this Autoconf
snippet:
AC_PROG_LEX
if test "$LEX" != flex; then
LEX="$SHELL $missing_dir/missing flex"
AC_SUBST([LEX_OUTPUT_ROOT], [lex.yy])
AC_SUBST([LEXLIB], [''])
fi
The shell script `missing' can be found in the Automake
distribution.
To ensure backward compatibility, Automake's `AM_PROG_LEX' invokes
(indirectly) this macro twice, which causes an annoying but benign
"`AC_PROG_LEX' invoked multiple times" warning. Future versions
of Automake will fix this issue; meanwhile, just ignore this
message.
As part of running the test, this macro may delete any file in the
configuration directory named `lex.yy.c' or `lexyy.c'.
-- Macro: AC_PROG_LN_S
If `ln -s' works on the current file system (the operating system
and file system support symbolic links), set the output variable
`LN_S' to `ln -s'; otherwise, if `ln' works, set `LN_S' to `ln',
and otherwise set it to `cp -p'.
If you make a link in a directory other than the current
directory, its meaning depends on whether `ln' or `ln -s' is used.
To safely create links using `$(LN_S)', either find out which
form is used and adjust the arguments, or always invoke `ln' in
the directory where the link is to be created.
In other words, it does not work to do:
$(LN_S) foo /x/bar
Instead, do:
(cd /x && $(LN_S) foo bar)
-- Macro: AC_PROG_RANLIB
Set output variable `RANLIB' to `ranlib' if `ranlib' is found, and
otherwise to `:' (do nothing).
-- Macro: AC_PROG_SED
Set output variable `SED' to a Sed implementation that conforms to
Posix and does not have arbitrary length limits. Report an error
if no acceptable Sed is found. *Note Limitations of Usual
Tools::, for more information about portability problems with Sed.
-- Macro: AC_PROG_YACC
If `bison' is found, set output variable `YACC' to `bison -y'.
Otherwise, if `byacc' is found, set `YACC' to `byacc'. Otherwise
set `YACC' to `yacc'.

File: autoconf.info, Node: Generic Programs, Prev: Particular Programs, Up: Alternative Programs
5.2.2 Generic Program and File Checks
-------------------------------------
These macros are used to find programs not covered by the "particular"
test macros. If you need to check the behavior of a program as well as
find out whether it is present, you have to write your own test for it
(*note Writing Tests::). By default, these macros use the environment
variable `PATH'. If you need to check for a program that might not be
in the user's `PATH', you can pass a modified path to use instead, like
this:
AC_PATH_PROG([INETD], [inetd], [/usr/libexec/inetd],
[$PATH:/usr/libexec:/usr/sbin:/usr/etc:/etc])
You are strongly encouraged to declare the VARIABLE passed to
`AC_CHECK_PROG' etc. as precious, *Note Setting Output Variables::,
`AC_ARG_VAR', for more details.
-- Macro: AC_CHECK_PROG (VARIABLE, PROG-TO-CHECK-FOR, VALUE-IF-FOUND,
[VALUE-IF-NOT-FOUND], [PATH], [REJECT])
Check whether program PROG-TO-CHECK-FOR exists in `PATH'. If it
is found, set VARIABLE to VALUE-IF-FOUND, otherwise to
VALUE-IF-NOT-FOUND, if given. Always pass over REJECT (an
absolute file name) even if it is the first found in the search
path; in that case, set VARIABLE using the absolute file name of
the PROG-TO-CHECK-FOR found that is not REJECT. If VARIABLE was
already set, do nothing. Calls `AC_SUBST' for VARIABLE.
-- Macro: AC_CHECK_PROGS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Check for each program in the blank-separated list
PROGS-TO-CHECK-FOR existing in the `PATH'. If one is found, set
VARIABLE to the name of that program. Otherwise, continue
checking the next program in the list. If none of the programs in
the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
changed. Calls `AC_SUBST' for VARIABLE.
-- Macro: AC_CHECK_TARGET_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a
prefix of the target type as determined by `AC_CANONICAL_TARGET',
followed by a dash (*note Canonicalizing::). If the tool cannot
be found with a prefix, and if the build and target types are
equal, then it is also searched for without a prefix.
As noted in *Note Specifying the system type: Specifying Names, the
target is rarely specified, because most of the time it is the same
as the host: it is the type of system for which any compiler tool
in the package produces code. What this macro looks for is, for
example, _a tool (assembler, linker, etc.) that the compiler
driver (`gcc' for the GNU C Compiler) uses to produce objects,
archives or executables_.
-- Macro: AC_CHECK_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a
prefix of the host type as determined by `AC_CANONICAL_HOST',
followed by a dash (*note Canonicalizing::). For example, if the
user runs `configure --host=i386-gnu', then this call:
AC_CHECK_TOOL([RANLIB], [ranlib], [:])
sets `RANLIB' to `i386-gnu-ranlib' if that program exists in
`PATH', or otherwise to `ranlib' if that program exists in `PATH',
or to `:' if neither program exists.
In the future, when cross-compiling this macro will _only_ accept
program names that are prefixed with the host type. For more
information, see *Note Specifying the system type: Specifying
Names.
-- Macro: AC_CHECK_TARGET_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_TARGET_TOOL', each of the tools in the list
PROGS-TO-CHECK-FOR are checked with a prefix of the target type as
determined by `AC_CANONICAL_TARGET', followed by a dash (*note
Canonicalizing::). If none of the tools can be found with a
prefix, and if the build and target types are equal, then the
first one without a prefix is used. If a tool is found, set
VARIABLE to the name of that program. If none of the tools in the
list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
changed. Calls `AC_SUBST' for VARIABLE.
-- Macro: AC_CHECK_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_TOOL', each of the tools in the list
PROGS-TO-CHECK-FOR are checked with a prefix of the host type as
determined by `AC_CANONICAL_HOST', followed by a dash (*note
Canonicalizing::). If none of the tools can be found with a
prefix, then the first one without a prefix is used. If a tool is
found, set VARIABLE to the name of that program. If none of the
tools in the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if
VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not
changed. Calls `AC_SUBST' for VARIABLE.
In the future, when cross-compiling this macro will _not_ accept
program names that are not prefixed with the host type.
-- Macro: AC_PATH_PROG (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_PROG', but set VARIABLE to the absolute name of
PROG-TO-CHECK-FOR if found.
-- Macro: AC_PATH_PROGS (VARIABLE, PROGS-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_PROGS', but if any of PROGS-TO-CHECK-FOR are found,
set VARIABLE to the absolute name of the program found.
-- Macro: AC_PATH_TARGET_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_TARGET_TOOL', but set VARIABLE to the absolute name
of the program if it is found.
-- Macro: AC_PATH_TOOL (VARIABLE, PROG-TO-CHECK-FOR,
[VALUE-IF-NOT-FOUND], [PATH])
Like `AC_CHECK_TOOL', but set VARIABLE to the absolute name of the
program if it is found.
In the future, when cross-compiling this macro will _not_ accept
program names that are not prefixed with the host type.

File: autoconf.info, Node: Files, Next: Libraries, Prev: Alternative Programs, Up: Existing Tests
5.3 Files
=========
You might also need to check for the existence of files. Before using
these macros, ask yourself whether a runtime test might not be a better
solution. Be aware that, like most Autoconf macros, they test a feature
of the host machine, and therefore, they die when cross-compiling.
-- Macro: AC_CHECK_FILE (FILE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Check whether file FILE exists on the native system. If it is
found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND,
if given.
-- Macro: AC_CHECK_FILES (FILES, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Executes `AC_CHECK_FILE' once for each file listed in FILES.
Additionally, defines `HAVE_FILE' (*note Standard Symbols::) for
each file found.

File: autoconf.info, Node: Libraries, Next: Library Functions, Prev: Files, Up: Existing Tests
5.4 Library Files
=================
The following macros check for the presence of certain C, C++, or
Fortran library archive files.
-- Macro: AC_CHECK_LIB (LIBRARY, FUNCTION, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
Test whether the library LIBRARY is available by trying to link a
test program that calls function FUNCTION with the library.
FUNCTION should be a function provided by the library. Use the
base name of the library; e.g., to check for `-lmp', use `mp' as
the LIBRARY argument.
ACTION-IF-FOUND is a list of shell commands to run if the link
with the library succeeds; ACTION-IF-NOT-FOUND is a list of shell
commands to run if the link fails. If ACTION-IF-FOUND is not
specified, the default action prepends `-lLIBRARY' to `LIBS' and
defines `HAVE_LIBLIBRARY' (in all capitals). This macro is
intended to support building `LIBS' in a right-to-left
(least-dependent to most-dependent) fashion such that library
dependencies are satisfied as a natural side effect of consecutive
tests. Linkers are sensitive to library ordering so the order in
which `LIBS' is generated is important to reliable detection of
libraries.
If linking with LIBRARY results in unresolved symbols that would
be resolved by linking with additional libraries, give those
libraries as the OTHER-LIBRARIES argument, separated by spaces:
e.g., `-lXt -lX11'. Otherwise, this macro fails to detect that
LIBRARY is present, because linking the test program always fails
with unresolved symbols. The OTHER-LIBRARIES argument should be
limited to cases where it is desirable to test for one library in
the presence of another that is not already in `LIBS'.
`AC_CHECK_LIB' requires some care in usage, and should be avoided
in some common cases. Many standard functions like `gethostbyname'
appear the standard C library on some hosts, and in special
libraries like `nsl' on other hosts. On some hosts the special
libraries contain variant implementations that you may not want to
use. These days it is normally better to use
`AC_SEARCH_LIBS([gethostbyname], [nsl])' instead of
`AC_CHECK_LIB([nsl], [gethostbyname])'.
-- Macro: AC_SEARCH_LIBS (FUNCTION, SEARCH-LIBS, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
Search for a library defining FUNCTION if it's not already
available. This equates to calling
`AC_LINK_IFELSE([AC_LANG_CALL([], [FUNCTION])])' first with no
libraries, then for each library listed in SEARCH-LIBS.
Add `-lLIBRARY' to `LIBS' for the first library found to contain
FUNCTION, and run ACTION-IF-FOUND. If the function is not found,
run ACTION-IF-NOT-FOUND.
If linking with LIBRARY results in unresolved symbols that would
be resolved by linking with additional libraries, give those
libraries as the OTHER-LIBRARIES argument, separated by spaces:
e.g., `-lXt -lX11'. Otherwise, this macro fails to detect that
FUNCTION is present, because linking the test program always fails
with unresolved symbols.

File: autoconf.info, Node: Library Functions, Next: Header Files, Prev: Libraries, Up: Existing Tests
5.5 Library Functions
=====================
The following macros check for particular C library functions. If
there is no macro specifically defined to check for a function you need,
and you don't need to check for any special properties of it, then you
can use one of the general function-check macros.
* Menu:
* Function Portability:: Pitfalls with usual functions
* Particular Functions:: Special handling to find certain functions
* Generic Functions:: How to find other functions

File: autoconf.info, Node: Function Portability, Next: Particular Functions, Up: Library Functions
5.5.1 Portability of C Functions
--------------------------------
Most usual functions can either be missing, or be buggy, or be limited
on some architectures. This section tries to make an inventory of these
portability issues. By definition, this list always requires
additions. Please help us keeping it as complete as possible.
`exit'
On ancient hosts, `exit' returned `int'. This is because `exit'
predates `void', and there was a long tradition of it returning
`int'.
On current hosts, the problem more likely is that `exit' is not
declared, due to C++ problems of some sort or another. For this
reason we suggest that test programs not invoke `exit', but return
from `main' instead.
`free'
The C standard says a call `free (NULL)' does nothing, but some
old systems don't support this (e.g., NextStep).
`isinf'
`isnan'
The C99 standard says that `isinf' and `isnan' are macros. On
some systems just macros are available (e.g., HP-UX and Solaris
10), on some systems both macros and functions (e.g., glibc
2.3.2), and on some systems only functions (e.g., IRIX 6 and
Solaris 9). In some cases these functions are declared in
nonstandard headers like `<sunmath.h>' and defined in non-default
libraries like `-lm' or `-lsunmath'.
The C99 `isinf' and `isnan' macros work correctly with `long
double' arguments, but pre-C99 systems that use functions
typically assume `double' arguments. On such a system, `isinf'
incorrectly returns true for a finite `long double' argument that
is outside the range of `double'.
To work around this porting mess, you can use code like the
following.
#include <math.h>
#ifndef isnan
# define isnan(x) \
(sizeof (x) == sizeof (long double) ? isnan_ld (x) \
: sizeof (x) == sizeof (double) ? isnan_d (x) \
: isnan_f (x))
static inline int isnan_f (float x) { return x != x; }
static inline int isnan_d (double x) { return x != x; }
static inline int isnan_ld (long double x) { return x != x; }
#endif
#ifndef isinf
# define isinf(x) \
(sizeof (x) == sizeof (long double) ? isinf_ld (x) \
: sizeof (x) == sizeof (double) ? isinf_d (x) \
: isinf_f (x))
static inline int isinf_f (float x) { return isnan (x - x); }
static inline int isinf_d (double x) { return isnan (x - x); }
static inline int isinf_ld (long double x) { return isnan (x - x); }
#endif
Use `AC_C_INLINE' (*note C Compiler::) so that this code works on
compilers that lack the `inline' keyword. Some optimizing
compilers mishandle these definitions, but systems with that bug
typically have missing or broken `isnan' functions anyway, so it's
probably not worth worrying about.
`malloc'
The C standard says a call `malloc (0)' is implementation
dependent. It can return either `NULL' or a new non-null pointer.
The latter is more common (e.g., the GNU C Library) but is by no
means universal. `AC_FUNC_MALLOC' can be used to insist on
non-`NULL' (*note Particular Functions::).
`putenv'
Posix prefers `setenv' to `putenv'; among other things, `putenv'
is not required of all Posix implementations, but `setenv' is.
Posix specifies that `putenv' puts the given string directly in
`environ', but some systems make a copy of it instead (e.g., glibc
2.0, or BSD). And when a copy is made, `unsetenv' might not free
it, causing a memory leak (e.g., FreeBSD 4).
On some systems `putenv ("FOO")' removes `FOO' from the
environment, but this is not standard usage and it dumps core on
some systems (e.g., AIX).
On MinGW, a call `putenv ("FOO=")' removes `FOO' from the
environment, rather than inserting it with an empty value.
`realloc'
The C standard says a call `realloc (NULL, size)' is equivalent to
`malloc (size)', but some old systems don't support this (e.g.,
NextStep).
`signal' handler
Normally `signal' takes a handler function with a return type of
`void', but some old systems required `int' instead. Any actual
`int' value returned is not used; this is only a difference in the
function prototype demanded.
All systems we know of in current use return `void'. The `int'
was to support K&R C, where of course `void' is not available.
`AC_TYPE_SIGNAL' (*note Particular Types::) can be used to
establish the correct type in all cases.
`snprintf'
The C99 standard says that if the output array isn't big enough
and if no other errors occur, `snprintf' and `vsnprintf' truncate
the output and return the number of bytes that ought to have been
produced. Some older systems return the truncated length (e.g.,
GNU C Library 2.0.x or IRIX 6.5), some a negative value (e.g.,
earlier GNU C Library versions), and some the buffer length
without truncation (e.g., 32-bit Solaris 7). Also, some buggy
older systems ignore the length and overrun the buffer (e.g.,
64-bit Solaris 7).
`sprintf'
The C standard says `sprintf' and `vsprintf' return the number of
bytes written. On some ancient systems (SunOS 4 for instance)
they return the buffer pointer instead, but these no longer need
to be worried about.
`sscanf'
On various old systems, e.g., HP-UX 9, `sscanf' requires that its
input string be writable (though it doesn't actually change it).
This can be a problem when using `gcc' since it normally puts
constant strings in read-only memory (*note Incompatibilities of
GCC: (gcc)Incompatibilities.). Apparently in some cases even
having format strings read-only can be a problem.
`strerror_r'
Posix specifies that `strerror_r' returns an `int', but many
systems (e.g., GNU C Library version 2.2.4) provide a different
version returning a `char *'. `AC_FUNC_STRERROR_R' can detect
which is in use (*note Particular Functions::).
`strnlen'
AIX 4.3 provides a broken version which produces the following
results:
strnlen ("foobar", 0) = 0
strnlen ("foobar", 1) = 3
strnlen ("foobar", 2) = 2
strnlen ("foobar", 3) = 1
strnlen ("foobar", 4) = 0
strnlen ("foobar", 5) = 6
strnlen ("foobar", 6) = 6
strnlen ("foobar", 7) = 6
strnlen ("foobar", 8) = 6
strnlen ("foobar", 9) = 6
`sysconf'
`_SC_PAGESIZE' is standard, but some older systems (e.g., HP-UX 9)
have `_SC_PAGE_SIZE' instead. This can be tested with `#ifdef'.
`unlink'
The Posix spec says that `unlink' causes the given file to be
removed only after there are no more open file handles for it.
Some non-Posix hosts have trouble with this requirement, though,
and some DOS variants even corrupt the file system.
`unsetenv'
On MinGW, `unsetenv' is not available, but a variable `FOO' can be
removed with a call `putenv ("FOO=")', as described under `putenv'
above.
`va_copy'
The C99 standard provides `va_copy' for copying `va_list'
variables. It may be available in older environments too, though
possibly as `__va_copy' (e.g., `gcc' in strict pre-C99 mode).
These can be tested with `#ifdef'. A fallback to `memcpy (&dst,
&src, sizeof (va_list))' gives maximum portability.
`va_list'
`va_list' is not necessarily just a pointer. It can be a `struct'
(e.g., `gcc' on Alpha), which means `NULL' is not portable. Or it
can be an array (e.g., `gcc' in some PowerPC configurations),
which means as a function parameter it can be effectively
call-by-reference and library routines might modify the value back
in the caller (e.g., `vsnprintf' in the GNU C Library 2.1).
Signed `>>'
Normally the C `>>' right shift of a signed type replicates the
high bit, giving a so-called "arithmetic" shift. But care should
be taken since Standard C doesn't require that behavior. On those
few processors without a native arithmetic shift (for instance Cray
vector systems) zero bits may be shifted in, the same as a shift
of an unsigned type.
Integer `/'
C divides signed integers by truncating their quotient toward zero,
yielding the same result as Fortran. However, before C99 the
standard allowed C implementations to take the floor or ceiling of
the quotient in some cases. Hardly any implementations took
advantage of this freedom, though, and it's probably not worth
worrying about this issue nowadays.

File: autoconf.info, Node: Particular Functions, Next: Generic Functions, Prev: Function Portability, Up: Library Functions
5.5.2 Particular Function Checks
--------------------------------
These macros check for particular C functions--whether they exist, and
in some cases how they respond when given certain arguments.
-- Macro: AC_FUNC_ALLOCA
Check how to get `alloca'. Tries to get a builtin version by
checking for `alloca.h' or the predefined C preprocessor macros
`__GNUC__' and `_AIX'. If this macro finds `alloca.h', it defines
`HAVE_ALLOCA_H'.
If those attempts fail, it looks for the function in the standard C
library. If any of those methods succeed, it defines
`HAVE_ALLOCA'. Otherwise, it sets the output variable `ALLOCA' to
`${LIBOBJDIR}alloca.o' and defines `C_ALLOCA' (so programs can
periodically call `alloca (0)' to garbage collect). This variable
is separate from `LIBOBJS' so multiple programs can share the
value of `ALLOCA' without needing to create an actual library, in
case only some of them use the code in `LIBOBJS'. The
`${LIBOBJDIR}' prefix serves the same purpose as in `LIBOBJS'
(*note AC_LIBOBJ vs LIBOBJS::).
This macro does not try to get `alloca' from the System V R3
`libPW' or the System V R4 `libucb' because those libraries
contain some incompatible functions that cause trouble. Some
versions do not even contain `alloca' or contain a buggy version.
If you still want to use their `alloca', use `ar' to extract
`alloca.o' from them instead of compiling `alloca.c'.
Source files that use `alloca' should start with a piece of code
like the following, to declare it properly.
#ifdef HAVE_ALLOCA_H
# include <alloca.h>
#elif defined __GNUC__
# define alloca __builtin_alloca
#elif defined _AIX
# define alloca __alloca
#elif defined _MSC_VER
# include <malloc.h>
# define alloca _alloca
#else
# include <stddef.h>
# ifdef __cplusplus
extern "C"
# endif
void *alloca (size_t);
#endif
-- Macro: AC_FUNC_CHOWN
If the `chown' function is available and works (in particular, it
should accept `-1' for `uid' and `gid'), define `HAVE_CHOWN'.
-- Macro: AC_FUNC_CLOSEDIR_VOID
If the `closedir' function does not return a meaningful value,
define `CLOSEDIR_VOID'. Otherwise, callers ought to check its
return value for an error indicator.
Currently this test is implemented by running a test program. When
cross compiling the pessimistic assumption that `closedir' does not
return a meaningful value is made.
This macro is obsolescent, as `closedir' returns a meaningful value
on current systems. New programs need not use this macro.
-- Macro: AC_FUNC_ERROR_AT_LINE
If the `error_at_line' function is not found, require an
`AC_LIBOBJ' replacement of `error'.
-- Macro: AC_FUNC_FNMATCH
If the `fnmatch' function conforms to Posix, define
`HAVE_FNMATCH'. Detect common implementation bugs, for example,
the bugs in Solaris 2.4.
Unlike the other specific `AC_FUNC' macros, `AC_FUNC_FNMATCH' does
not replace a broken/missing `fnmatch'. This is for historical
reasons. See `AC_REPLACE_FNMATCH' below.
This macro is obsolescent. New programs should use Gnulib's
`fnmatch-posix' module. *Note Gnulib::.
-- Macro: AC_FUNC_FNMATCH_GNU
Behave like `AC_REPLACE_FNMATCH' (_replace_) but also test whether
`fnmatch' supports GNU extensions. Detect common implementation
bugs, for example, the bugs in the GNU C Library 2.1.
This macro is obsolescent. New programs should use Gnulib's
`fnmatch-gnu' module. *Note Gnulib::.
-- Macro: AC_FUNC_FORK
This macro checks for the `fork' and `vfork' functions. If a
working `fork' is found, define `HAVE_WORKING_FORK'. This macro
checks whether `fork' is just a stub by trying to run it.
If `vfork.h' is found, define `HAVE_VFORK_H'. If a working
`vfork' is found, define `HAVE_WORKING_VFORK'. Otherwise, define
`vfork' to be `fork' for backward compatibility with previous
versions of `autoconf'. This macro checks for several known
errors in implementations of `vfork' and considers the system to
not have a working `vfork' if it detects any of them. It is not
considered to be an implementation error if a child's invocation
of `signal' modifies the parent's signal handler, since child
processes rarely change their signal handlers.
Since this macro defines `vfork' only for backward compatibility
with previous versions of `autoconf' you're encouraged to define it
yourself in new code:
#ifndef HAVE_WORKING_VFORK
# define vfork fork
#endif
-- Macro: AC_FUNC_FSEEKO
If the `fseeko' function is available, define `HAVE_FSEEKO'.
Define `_LARGEFILE_SOURCE' if necessary to make the prototype
visible on some systems (e.g., glibc 2.2). Otherwise linkage
problems may occur when compiling with `AC_SYS_LARGEFILE' on
largefile-sensitive systems where `off_t' does not default to a
64bit entity.
-- Macro: AC_FUNC_GETGROUPS
If the `getgroups' function is available and works (unlike on
Ultrix 4.3, where `getgroups (0, 0)' always fails), define
`HAVE_GETGROUPS'. Set `GETGROUPS_LIBS' to any libraries needed to
get that function. This macro runs `AC_TYPE_GETGROUPS'.
-- Macro: AC_FUNC_GETLOADAVG
Check how to get the system load averages. To perform its tests
properly, this macro needs the file `getloadavg.c'; therefore, be
sure to set the `AC_LIBOBJ' replacement directory properly (see
*Note Generic Functions::, `AC_CONFIG_LIBOBJ_DIR').
If the system has the `getloadavg' function, define
`HAVE_GETLOADAVG', and set `GETLOADAVG_LIBS' to any libraries
necessary to get that function. Also add `GETLOADAVG_LIBS' to
`LIBS'. Otherwise, require an `AC_LIBOBJ' replacement for
`getloadavg' with source code in `DIR/getloadavg.c', and possibly
define several other C preprocessor macros and output variables:
1. Define `C_GETLOADAVG'.
2. Define `SVR4', `DGUX', `UMAX', or `UMAX4_3' if on those
systems.
3. If `nlist.h' is found, define `HAVE_NLIST_H'.
4. If `struct nlist' has an `n_un.n_name' member, define
`HAVE_STRUCT_NLIST_N_UN_N_NAME'. The obsolete symbol
`NLIST_NAME_UNION' is still defined, but do not depend upon
it.
5. Programs may need to be installed set-group-ID (or
set-user-ID) for `getloadavg' to work. In this case, define
`GETLOADAVG_PRIVILEGED', set the output variable `NEED_SETGID'
to `true' (and otherwise to `false'), and set `KMEM_GROUP' to
the name of the group that should own the installed program.
The `AC_FUNC_GETLOADVG' macro is obsolescent. New programs should
use Gnulib's `getloadavg' module. *Note Gnulib::.
-- Macro: AC_FUNC_GETMNTENT
Check for `getmntent' in the standard C library, and then in the
`sun', `seq', and `gen' libraries, for UNICOS, IRIX 4, PTX, and
UnixWare, respectively. Then, if `getmntent' is available, define
`HAVE_GETMNTENT'.
-- Macro: AC_FUNC_GETPGRP
Define `GETPGRP_VOID' if it is an error to pass 0 to `getpgrp';
this is the Posix behavior. On older BSD systems, you must pass 0
to `getpgrp', as it takes an argument and behaves like Posix's
`getpgid'.
#ifdef GETPGRP_VOID
pid = getpgrp ();
#else
pid = getpgrp (0);
#endif
This macro does not check whether `getpgrp' exists at all; if you
need to work in that situation, first call `AC_CHECK_FUNC' for
`getpgrp'.
This macro is obsolescent, as current systems have a `getpgrp'
whose signature conforms to Posix. New programs need not use this
macro.
-- Macro: AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
If `link' is a symbolic link, then `lstat' should treat `link/'
the same as `link/.'. However, many older `lstat' implementations
incorrectly ignore trailing slashes.
It is safe to assume that if `lstat' incorrectly ignores trailing
slashes, then other symbolic-link-aware functions like `unlink'
also incorrectly ignore trailing slashes.
If `lstat' behaves properly, define
`LSTAT_FOLLOWS_SLASHED_SYMLINK', otherwise require an `AC_LIBOBJ'
replacement of `lstat'.
-- Macro: AC_FUNC_MALLOC
If the `malloc' function is compatible with the GNU C library
`malloc' (i.e., `malloc (0)' returns a valid pointer), define
`HAVE_MALLOC' to 1. Otherwise define `HAVE_MALLOC' to 0, ask for
an `AC_LIBOBJ' replacement for `malloc', and define `malloc' to
`rpl_malloc' so that the native `malloc' is not used in the main
project.
Typically, the replacement file `malloc.c' should look like (note
the `#undef malloc'):
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#undef malloc
#include <sys/types.h>
void *malloc ();
/* Allocate an N-byte block of memory from the heap.
If N is zero, allocate a 1-byte block. */
void *
rpl_malloc (size_t n)
{
if (n == 0)
n = 1;
return malloc (n);
}
-- Macro: AC_FUNC_MEMCMP
If the `memcmp' function is not available, or does not work on
8-bit data (like the one on SunOS 4.1.3), or fails when comparing
16 bytes or more and with at least one buffer not starting on a
4-byte boundary (such as the one on NeXT x86 OpenStep), require an
`AC_LIBOBJ' replacement for `memcmp'.
This macro is obsolescent, as current systems have a working
`memcmp'. New programs need not use this macro.
-- Macro: AC_FUNC_MBRTOWC
Define `HAVE_MBRTOWC' to 1 if the function `mbrtowc' and the type
`mbstate_t' are properly declared.
-- Macro: AC_FUNC_MKTIME
If the `mktime' function is not available, or does not work
correctly, require an `AC_LIBOBJ' replacement for `mktime'. For
the purposes of this test, `mktime' should conform to the Posix
standard and should be the inverse of `localtime'.
-- Macro: AC_FUNC_MMAP
If the `mmap' function exists and works correctly, define
`HAVE_MMAP'. This checks only private fixed mapping of
already-mapped memory.
-- Macro: AC_FUNC_OBSTACK
If the obstacks are found, define `HAVE_OBSTACK', else require an
`AC_LIBOBJ' replacement for `obstack'.
-- Macro: AC_FUNC_REALLOC
If the `realloc' function is compatible with the GNU C library
`realloc' (i.e., `realloc (NULL, 0)' returns a valid pointer),
define `HAVE_REALLOC' to 1. Otherwise define `HAVE_REALLOC' to 0,
ask for an `AC_LIBOBJ' replacement for `realloc', and define
`realloc' to `rpl_realloc' so that the native `realloc' is not
used in the main project. See `AC_FUNC_MALLOC' for details.
-- Macro: AC_FUNC_SELECT_ARGTYPES
Determines the correct type to be passed for each of the `select'
function's arguments, and defines those types in
`SELECT_TYPE_ARG1', `SELECT_TYPE_ARG234', and `SELECT_TYPE_ARG5'
respectively. `SELECT_TYPE_ARG1' defaults to `int',
`SELECT_TYPE_ARG234' defaults to `int *', and `SELECT_TYPE_ARG5'
defaults to `struct timeval *'.
This macro is obsolescent, as current systems have a `select' whose
signature conforms to Posix. New programs need not use this macro.
-- Macro: AC_FUNC_SETPGRP
If `setpgrp' takes no argument (the Posix version), define
`SETPGRP_VOID'. Otherwise, it is the BSD version, which takes two
process IDs as arguments. This macro does not check whether
`setpgrp' exists at all; if you need to work in that situation,
first call `AC_CHECK_FUNC' for `setpgrp'.
This macro is obsolescent, as current systems have a `setpgrp'
whose signature conforms to Posix. New programs need not use this
macro.
-- Macro: AC_FUNC_STAT
-- Macro: AC_FUNC_LSTAT
Determine whether `stat' or `lstat' have the bug that it succeeds
when given the zero-length file name as argument. The `stat' and
`lstat' from SunOS 4.1.4 and the Hurd (as of 1998-11-01) do this.
If it does, then define `HAVE_STAT_EMPTY_STRING_BUG' (or
`HAVE_LSTAT_EMPTY_STRING_BUG') and ask for an `AC_LIBOBJ'
replacement of it.
These macros are obsolescent, as no current systems have the bug.
New programs need not use these macros.
-- Macro: AC_FUNC_SETVBUF_REVERSED
If `setvbuf' takes the buffering type as its second argument and
the buffer pointer as the third, instead of the other way around,
define `SETVBUF_REVERSED'.
This macro is obsolescent, as no current systems have the bug.
New programs need not use this macro.
-- Macro: AC_FUNC_STRCOLL
If the `strcoll' function exists and works correctly, define
`HAVE_STRCOLL'. This does a bit more than
`AC_CHECK_FUNCS(strcoll)', because some systems have incorrect
definitions of `strcoll' that should not be used.
-- Macro: AC_FUNC_STRERROR_R
If `strerror_r' is available, define `HAVE_STRERROR_R', and if it
is declared, define `HAVE_DECL_STRERROR_R'. If it returns a `char
*' message, define `STRERROR_R_CHAR_P'; otherwise it returns an
`int' error number. The Thread-Safe Functions option of Posix
requires `strerror_r' to return `int', but many systems
(including, for example, version 2.2.4 of the GNU C Library)
return a `char *' value that is not necessarily equal to the
buffer argument.
-- Macro: AC_FUNC_STRFTIME
Check for `strftime' in the `intl' library, for SCO Unix. Then,
if `strftime' is available, define `HAVE_STRFTIME'.
This macro is obsolescent, as no current systems require the `intl'
library for `strftime'. New programs need not use this macro.
-- Macro: AC_FUNC_STRTOD
If the `strtod' function does not exist or doesn't work correctly,
ask for an `AC_LIBOBJ' replacement of `strtod'. In this case,
because `strtod.c' is likely to need `pow', set the output
variable `POW_LIB' to the extra library needed.
-- Macro: AC_FUNC_STRTOLD
If the `strtold' function exists and conforms to C99, define
`HAVE_STRTOLD'.
-- Macro: AC_FUNC_STRNLEN
If the `strnlen' function is not available, or is buggy (like the
one from AIX 4.3), require an `AC_LIBOBJ' replacement for it.
-- Macro: AC_FUNC_UTIME_NULL
If `utime (FILE, NULL)' sets FILE's timestamp to the present,
define `HAVE_UTIME_NULL'.
This macro is obsolescent, as all current systems have a `utime'
that behaves this way. New programs need not use this macro.
-- Macro: AC_FUNC_VPRINTF
If `vprintf' is found, define `HAVE_VPRINTF'. Otherwise, if
`_doprnt' is found, define `HAVE_DOPRNT'. (If `vprintf' is
available, you may assume that `vfprintf' and `vsprintf' are also
available.)
This macro is obsolescent, as all current systems have `vprintf'.
New programs need not use this macro.
-- Macro: AC_REPLACE_FNMATCH
If the `fnmatch' function does not conform to Posix (see
`AC_FUNC_FNMATCH'), ask for its `AC_LIBOBJ' replacement.
The files `fnmatch.c', `fnmatch_loop.c', and `fnmatch_.h' in the
`AC_LIBOBJ' replacement directory are assumed to contain a copy of
the source code of GNU `fnmatch'. If necessary, this source code
is compiled as an `AC_LIBOBJ' replacement, and the `fnmatch_.h'
file is linked to `fnmatch.h' so that it can be included in place
of the system `<fnmatch.h>'.
This macro is obsolescent, as it assumes the use of particular
source files. New programs should use Gnulib's `fnmatch-posix'
module, which provides this macro along with the source files.
*Note Gnulib::.

File: autoconf.info, Node: Generic Functions, Prev: Particular Functions, Up: Library Functions
5.5.3 Generic Function Checks
-----------------------------
These macros are used to find functions not covered by the "particular"
test macros. If the functions might be in libraries other than the
default C library, first call `AC_CHECK_LIB' for those libraries. If
you need to check the behavior of a function as well as find out
whether it is present, you have to write your own test for it (*note
Writing Tests::).
-- Macro: AC_CHECK_FUNC (FUNCTION, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
If C function FUNCTION is available, run shell commands
ACTION-IF-FOUND, otherwise ACTION-IF-NOT-FOUND. If you just want
to define a symbol if the function is available, consider using
`AC_CHECK_FUNCS' instead. This macro checks for functions with C
linkage even when `AC_LANG(C++)' has been called, since C is more
standardized than C++. (*note Language Choice::, for more
information about selecting the language for checks.)
-- Macro: AC_CHECK_FUNCS (FUNCTION..., [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
For each FUNCTION enumerated in the blank-or-newline-separated
argument list, define `HAVE_FUNCTION' (in all capitals) if it is
available. If ACTION-IF-FOUND is given, it is additional shell
code to execute when one of the functions is found. You can give
it a value of `break' to break out of the loop on the first match.
If ACTION-IF-NOT-FOUND is given, it is executed when one of the
functions is not found.
-- Macro: AC_CHECK_FUNCS_ONCE (FUNCTION...)
For each FUNCTION enumerated in the blank-or-newline-separated
argument list, define `HAVE_FUNCTION' (in all capitals) if it is
available. This is a once-only variant of `AC_CHECK_FUNCS'. It
generates the checking code at most once, so that `configure' is
smaller and faster; but the checks cannot be conditionalized and
are always done once, early during the `configure' run.
Autoconf follows a philosophy that was formed over the years by those
who have struggled for portability: isolate the portability issues in
specific files, and then program as if you were in a Posix environment.
Some functions may be missing or unfixable, and your package must be
ready to replace them.
Suitable replacements for many such problem functions are available
from Gnulib (*note Gnulib::).
-- Macro: AC_LIBOBJ (FUNCTION)
Specify that `FUNCTION.c' must be included in the executables to
replace a missing or broken implementation of FUNCTION.
Technically, it adds `FUNCTION.$ac_objext' to the output variable
`LIBOBJS' if it is not already in, and calls `AC_LIBSOURCE' for
`FUNCTION.c'. You should not directly change `LIBOBJS', since
this is not traceable.
-- Macro: AC_LIBSOURCE (FILE)
Specify that FILE might be needed to compile the project. If you
need to know what files might be needed by a `configure.ac', you
should trace `AC_LIBSOURCE'. FILE must be a literal.
This macro is called automatically from `AC_LIBOBJ', but you must
call it explicitly if you pass a shell variable to `AC_LIBOBJ'. In
that case, since shell variables cannot be traced statically, you
must pass to `AC_LIBSOURCE' any possible files that the shell
variable might cause `AC_LIBOBJ' to need. For example, if you
want to pass a variable `$foo_or_bar' to `AC_LIBOBJ' that holds
either `"foo"' or `"bar"', you should do:
AC_LIBSOURCE([foo.c])
AC_LIBSOURCE([bar.c])
AC_LIBOBJ([$foo_or_bar])
There is usually a way to avoid this, however, and you are
encouraged to simply call `AC_LIBOBJ' with literal arguments.
Note that this macro replaces the obsolete `AC_LIBOBJ_DECL', with
slightly different semantics: the old macro took the function name,
e.g., `foo', as its argument rather than the file name.
-- Macro: AC_LIBSOURCES (FILES)
Like `AC_LIBSOURCE', but accepts one or more FILES in a
comma-separated M4 list. Thus, the above example might be
rewritten:
AC_LIBSOURCES([foo.c, bar.c])
AC_LIBOBJ([$foo_or_bar])
-- Macro: AC_CONFIG_LIBOBJ_DIR (DIRECTORY)
Specify that `AC_LIBOBJ' replacement files are to be found in
DIRECTORY, a name relative to the top level of the source tree.
The replacement directory defaults to `.', the top level
directory, and the most typical value is `lib', corresponding to
`AC_CONFIG_LIBOBJ_DIR([lib])'.
`configure' might need to know the replacement directory for the
following reasons: (i) some checks use the replacement files, (ii)
some macros bypass broken system headers by installing links to the
replacement headers (iii) when used in conjunction with Automake,
within each makefile, DIRECTORY is used as a relative path from
`$(top_srcdir)' to each object named in `LIBOBJS' and `LTLIBOBJS',
etc.
It is common to merely check for the existence of a function, and ask
for its `AC_LIBOBJ' replacement if missing. The following macro is a
convenient shorthand.
-- Macro: AC_REPLACE_FUNCS (FUNCTION...)
Like `AC_CHECK_FUNCS', but uses `AC_LIBOBJ(FUNCTION)' as
ACTION-IF-NOT-FOUND. You can declare your replacement function by
enclosing the prototype in `#ifndef HAVE_FUNCTION'. If the system
has the function, it probably declares it in a header file you
should be including, so you shouldn't redeclare it lest your
declaration conflict.

File: autoconf.info, Node: Header Files, Next: Declarations, Prev: Library Functions, Up: Existing Tests
5.6 Header Files
================
The following macros check for the presence of certain C header files.
If there is no macro specifically defined to check for a header file
you need, and you don't need to check for any special properties of it,
then you can use one of the general header-file check macros.
* Menu:
* Header Portability:: Collected knowledge on common headers
* Particular Headers:: Special handling to find certain headers
* Generic Headers:: How to find other headers

File: autoconf.info, Node: Header Portability, Next: Particular Headers, Up: Header Files
5.6.1 Portability of Headers
----------------------------
This section tries to collect knowledge about common headers, and the
problems they cause. By definition, this list always requires
additions. Please help us keeping it as complete as possible.
`limits.h'
C99 says that `limits.h' defines `LLONG_MIN', `LLONG_MAX', and
`ULLONG_MAX', but many almost-C99 environments (e.g., default GCC
4.0.2 + glibc 2.4) do not define them.
`inttypes.h' vs. `stdint.h'
The C99 standard says that `inttypes.h' includes `stdint.h', so
there's no need to include `stdint.h' separately in a standard
environment. Some implementations have `inttypes.h' but not
`stdint.h' (e.g., Solaris 7), but we don't know of any
implementation that has `stdint.h' but not `inttypes.h'.
`linux/irda.h'
It requires `linux/types.h' and `sys/socket.h'.
`linux/random.h'
It requires `linux/types.h'.
`net/if.h'
On Darwin, this file requires that `sys/socket.h' be included
beforehand. One should run:
AC_CHECK_HEADERS([sys/socket.h])
AC_CHECK_HEADERS([net/if.h], [], [],
[#include <stdio.h>
#ifdef STDC_HEADERS
# include <stdlib.h>
# include <stddef.h>
#else
# ifdef HAVE_STDLIB_H
# include <stdlib.h>
# endif
#endif
#ifdef HAVE_SYS_SOCKET_H
# include <sys/socket.h>
#endif
])
`netinet/if_ether.h'
On Darwin, this file requires that `stdio.h' and `sys/socket.h' be
included beforehand. One should run:
AC_CHECK_HEADERS([sys/socket.h])
AC_CHECK_HEADERS([netinet/if_ether.h], [], [],
[#include <stdio.h>
#ifdef STDC_HEADERS
# include <stdlib.h>
# include <stddef.h>
#else
# ifdef HAVE_STDLIB_H
# include <stdlib.h>
# endif
#endif
#ifdef HAVE_SYS_SOCKET_H
# include <sys/socket.h>
#endif
])
`stdint.h'
See above, item `inttypes.h' vs. `stdint.h'.
`stdlib.h'
On many systems (e.g., Darwin), `stdio.h' is a prerequisite.
`sys/mount.h'
On FreeBSD 4.8 on ia32 and using gcc version 2.95.4,
`sys/params.h' is a prerequisite.
`sys/ptem.h'
On Solaris 8, `sys/stream.h' is a prerequisite.
`sys/socket.h'
On Darwin, `stdlib.h' is a prerequisite.
`sys/ucred.h'
On Tru64 5.1, `sys/types.h' is a prerequisite.
`X11/extensions/scrnsaver.h'
Using XFree86, this header requires `X11/Xlib.h', which is probably
so required that you might not even consider looking for it.
AC_CHECK_HEADERS([X11/extensions/scrnsaver.h], [], [],
[[#include <X11/Xlib.h>
]])

File: autoconf.info, Node: Particular Headers, Next: Generic Headers, Prev: Header Portability, Up: Header Files
5.6.2 Particular Header Checks
------------------------------
These macros check for particular system header files--whether they
exist, and in some cases whether they declare certain symbols.
-- Macro: AC_HEADER_ASSERT
Check whether to enable assertions in the style of `assert.h'.
Assertions are enabled by default, but the user can override this
by invoking `configure' with the `--disable-assert' option.
-- Macro: AC_HEADER_DIRENT
Check for the following header files. For the first one that is
found and defines `DIR', define the listed C preprocessor macro:
`dirent.h' `HAVE_DIRENT_H'
`sys/ndir.h' `HAVE_SYS_NDIR_H'
`sys/dir.h' `HAVE_SYS_DIR_H'
`ndir.h' `HAVE_NDIR_H'
The directory-library declarations in your source code should look
something like the following:
#include <sys/types.h>
#ifdef HAVE_DIRENT_H
# include <dirent.h>
# define NAMLEN(dirent) strlen ((dirent)->d_name)
#else
# define dirent direct
# define NAMLEN(dirent) ((dirent)->d_namlen)
# ifdef HAVE_SYS_NDIR_H
# include <sys/ndir.h>
# endif
# ifdef HAVE_SYS_DIR_H
# include <sys/dir.h>
# endif
# ifdef HAVE_NDIR_H
# include <ndir.h>
# endif
#endif
Using the above declarations, the program would declare variables
to be of type `struct dirent', not `struct direct', and would
access the length of a directory entry name by passing a pointer
to a `struct dirent' to the `NAMLEN' macro.
This macro also checks for the SCO Xenix `dir' and `x' libraries.
This macro is obsolescent, as all current systems with directory
libraries have `<dirent.h>'. New programs need not use this macro.
Also see `AC_STRUCT_DIRENT_D_INO' and `AC_STRUCT_DIRENT_D_TYPE'
(*note Particular Structures::).
-- Macro: AC_HEADER_MAJOR
If `sys/types.h' does not define `major', `minor', and `makedev',
but `sys/mkdev.h' does, define `MAJOR_IN_MKDEV'; otherwise, if
`sys/sysmacros.h' does, define `MAJOR_IN_SYSMACROS'.
-- Macro: AC_HEADER_RESOLV
Checks for header `resolv.h', checking for prerequisites first.
To properly use `resolv.h', your code should contain something like
the following:
#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif
#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h> /* inet_ functions / structs */
#endif
#ifdef HAVE_ARPA_NAMESER_H
# include <arpa/nameser.h> /* DNS HEADER struct */
#endif
#ifdef HAVE_NETDB_H
# include <netdb.h>
#endif
#include <resolv.h>
-- Macro: AC_HEADER_STAT
If the macros `S_ISDIR', `S_ISREG', etc. defined in `sys/stat.h'
do not work properly (returning false positives), define
`STAT_MACROS_BROKEN'. This is the case on Tektronix UTekV, Amdahl
UTS and Motorola System V/88.
This macro is obsolescent, as no current systems have the bug.
New programs need not use this macro.
-- Macro: AC_HEADER_STDBOOL
If `stdbool.h' exists and conforms to C99, define `HAVE_STDBOOL_H'
to 1; if the type `_Bool' is defined, define `HAVE__BOOL' to 1.
To fulfill the C99 requirements, your `system.h' could contain the
following code:
#ifdef HAVE_STDBOOL_H
# include <stdbool.h>
#else
# ifndef HAVE__BOOL
# ifdef __cplusplus
typedef bool _Bool;
# else
# define _Bool signed char
# endif
# endif
# define bool _Bool
# define false 0
# define true 1
# define __bool_true_false_are_defined 1
#endif
Alternatively you can use the `stdbool' package of Gnulib (*note
Gnulib::); it packages the above code into a replacement header
and contains a few other bells and whistles.
-- Macro: AC_HEADER_STDC
Define `STDC_HEADERS' if the system has C header files conforming
to ANSI C89 (ISO C90). Specifically, this macro checks for
`stdlib.h', `stdarg.h', `string.h', and `float.h'; if the system
has those, it probably has the rest of the C89 header files. This
macro also checks whether `string.h' declares `memchr' (and thus
presumably the other `mem' functions), whether `stdlib.h' declare
`free' (and thus presumably `malloc' and other related functions),
and whether the `ctype.h' macros work on characters with the high
bit set, as the C standard requires.
If you use this macro, your code can refer to `STDC_HEADERS' to
determine whether the system has conforming header files (and
probably C library functions).
This macro is obsolescent, as current systems have conforming
header files. New programs need not use this macro.
Nowadays `string.h' is part of the C standard and declares
functions like `strcpy', and `strings.h' is standardized by Posix
and declares BSD functions like `bcopy'; but historically, string
functions were a major sticking point in this area. If you still
want to worry about portability to ancient systems without
standard headers, there is so much variation that it is probably
easier to declare the functions you use than to figure out exactly
what the system header files declare. Some ancient systems
contained a mix of functions from the C standard and from BSD;
some were mostly standard but lacked `memmove'; some defined the
BSD functions as macros in `string.h' or `strings.h'; some had
only the BSD functions but `string.h'; some declared the memory
functions in `memory.h', some in `string.h'; etc. It is probably
sufficient to check for one string function and one memory
function; if the library had the standard versions of those then
it probably had most of the others. If you put the following in
`configure.ac':
# This example is obsolescent.
# Nowadays you can omit these macro calls.
AC_HEADER_STDC
AC_CHECK_FUNCS([strchr memcpy])
then, in your code, you can use declarations like this:
/* This example is obsolescent.
Nowadays you can just #include <string.h>. */
#ifdef STDC_HEADERS
# include <string.h>
#else
# ifndef HAVE_STRCHR
# define strchr index
# define strrchr rindex
# endif
char *strchr (), *strrchr ();
# ifndef HAVE_MEMCPY
# define memcpy(d, s, n) bcopy ((s), (d), (n))
# define memmove(d, s, n) bcopy ((s), (d), (n))
# endif
#endif
If you use a function like `memchr', `memset', `strtok', or
`strspn', which have no BSD equivalent, then macros don't suffice
to port to ancient hosts; you must provide an implementation of
each function. An easy way to incorporate your implementations
only when needed (since the ones in system C libraries may be hand
optimized) is to, taking `memchr' for example, put it in
`memchr.c' and use `AC_REPLACE_FUNCS([memchr])'.
-- Macro: AC_HEADER_SYS_WAIT
If `sys/wait.h' exists and is compatible with Posix, define
`HAVE_SYS_WAIT_H'. Incompatibility can occur if `sys/wait.h' does
not exist, or if it uses the old BSD `union wait' instead of `int'
to store a status value. If `sys/wait.h' is not Posix compatible,
then instead of including it, define the Posix macros with their
usual interpretations. Here is an example:
#include <sys/types.h>
#ifdef HAVE_SYS_WAIT_H
# include <sys/wait.h>
#endif
#ifndef WEXITSTATUS
# define WEXITSTATUS(stat_val) ((unsigned int) (stat_val) >> 8)
#endif
#ifndef WIFEXITED
# define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
#endif
This macro is obsolescent, as current systems are compatible with
Posix. New programs need not use this macro.
`_POSIX_VERSION' is defined when `unistd.h' is included on Posix
systems. If there is no `unistd.h', it is definitely not a Posix
system. However, some non-Posix systems do have `unistd.h'.
The way to check whether the system supports Posix is:
#ifdef HAVE_UNISTD_H
# include <sys/types.h>
# include <unistd.h>
#endif
#ifdef _POSIX_VERSION
/* Code for Posix systems. */
#endif
-- Macro: AC_HEADER_TIME
If a program may include both `time.h' and `sys/time.h', define
`TIME_WITH_SYS_TIME'. On some ancient systems, `sys/time.h'
included `time.h', but `time.h' was not protected against multiple
inclusion, so programs could not explicitly include both files.
This macro is useful in programs that use, for example, `struct
timeval' as well as `struct tm'. It is best used in conjunction
with `HAVE_SYS_TIME_H', which can be checked for using
`AC_CHECK_HEADERS([sys/time.h])'.
#ifdef TIME_WITH_SYS_TIME
# include <sys/time.h>
# include <time.h>
#else
# ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
# else
# include <time.h>
# endif
#endif
This macro is obsolescent, as current systems can include both
files when they exist. New programs need not use this macro.
-- Macro: AC_HEADER_TIOCGWINSZ
If the use of `TIOCGWINSZ' requires `<sys/ioctl.h>', then define
`GWINSZ_IN_SYS_IOCTL'. Otherwise `TIOCGWINSZ' can be found in
`<termios.h>'.
Use:
#ifdef HAVE_TERMIOS_H
# include <termios.h>
#endif
#ifdef GWINSZ_IN_SYS_IOCTL
# include <sys/ioctl.h>
#endif

File: autoconf.info, Node: Generic Headers, Prev: Particular Headers, Up: Header Files
5.6.3 Generic Header Checks
---------------------------
These macros are used to find system header files not covered by the
"particular" test macros. If you need to check the contents of a header
as well as find out whether it is present, you have to write your own
test for it (*note Writing Tests::).
-- Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
If the system header file HEADER-FILE is compilable, execute shell
commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
If you just want to define a symbol if the header file is
available, consider using `AC_CHECK_HEADERS' instead.
For compatibility issues with older versions of Autoconf, please
read below.
-- Macro: AC_CHECK_HEADERS (HEADER-FILE..., [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
For each given system header file HEADER-FILE in the
blank-separated argument list that exists, define
`HAVE_HEADER-FILE' (in all capitals). If ACTION-IF-FOUND is
given, it is additional shell code to execute when one of the
header files is found. You can give it a value of `break' to
break out of the loop on the first match. If ACTION-IF-NOT-FOUND
is given, it is executed when one of the header files is not found.
For compatibility issues with older versions of Autoconf, please
read below.
Previous versions of Autoconf merely checked whether the header was
accepted by the preprocessor. This was changed because the old test was
inappropriate for typical uses. Headers are typically used to compile,
not merely to preprocess, and the old behavior sometimes accepted
headers that clashed at compile-time. If you need to check whether a
header is preprocessable, you can use `AC_PREPROC_IFELSE' (*note
Running the Preprocessor::).
This scheme, which improves the robustness of the test, also requires
that you make sure that headers that must be included before the
HEADER-FILE be part of the INCLUDES, (*note Default Includes::). If
looking for `bar.h', which requires that `foo.h' be included before if
it exists, we suggest the following scheme:
AC_CHECK_HEADERS([foo.h])
AC_CHECK_HEADERS([bar.h], [], [],
[#ifdef HAVE_FOO_H
# include <foo.h>
# endif
])
The following variant generates smaller, faster `configure' files if
you do not need the full power of `AC_CHECK_HEADERS'.
-- Macro: AC_CHECK_HEADERS_ONCE (HEADER-FILE...)
For each given system header file HEADER-FILE in the
blank-separated argument list that exists, define
`HAVE_HEADER-FILE' (in all capitals). This is a once-only variant
of `AC_CHECK_HEADERS'. It generates the checking code at most
once, so that `configure' is smaller and faster; but the checks
cannot be conditionalized and are always done once, early during
the `configure' run.

File: autoconf.info, Node: Declarations, Next: Structures, Prev: Header Files, Up: Existing Tests
5.7 Declarations
================
The following macros check for the declaration of variables and
functions. If there is no macro specifically defined to check for a
symbol you need, then you can use the general macros (*note Generic
Declarations::) or, for more complex tests, you may use
`AC_COMPILE_IFELSE' (*note Running the Compiler::).
* Menu:
* Particular Declarations:: Macros to check for certain declarations
* Generic Declarations:: How to find other declarations

File: autoconf.info, Node: Particular Declarations, Next: Generic Declarations, Up: Declarations
5.7.1 Particular Declaration Checks
-----------------------------------
There are no specific macros for declarations.

File: autoconf.info, Node: Generic Declarations, Prev: Particular Declarations, Up: Declarations
5.7.2 Generic Declaration Checks
--------------------------------
These macros are used to find declarations not covered by the
"particular" test macros.
-- Macro: AC_CHECK_DECL (SYMBOL, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
If SYMBOL (a function, variable, or constant) is not declared in
INCLUDES and a declaration is needed, run the shell commands
ACTION-IF-NOT-FOUND, otherwise ACTION-IF-FOUND. If no INCLUDES
are specified, the default includes are used (*note Default
Includes::).
This macro actually tests whether SYMBOL is defined as a macro or
can be used as an r-value, not whether it is really declared,
because it is much safer to avoid introducing extra declarations
when they are not needed.
-- Macro: AC_CHECK_DECLS (SYMBOLS, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
For each of the SYMBOLS (_comma_-separated list), define
`HAVE_DECL_SYMBOL' (in all capitals) to `1' if SYMBOL is declared,
otherwise to `0'. If ACTION-IF-NOT-FOUND is given, it is
additional shell code to execute when one of the function
declarations is needed, otherwise ACTION-IF-FOUND is executed.
This macro uses an M4 list as first argument:
AC_CHECK_DECLS([strdup])
AC_CHECK_DECLS([strlen])
AC_CHECK_DECLS([malloc, realloc, calloc, free])
Unlike the other `AC_CHECK_*S' macros, when a SYMBOL is not
declared, `HAVE_DECL_SYMBOL' is defined to `0' instead of leaving
`HAVE_DECL_SYMBOL' undeclared. When you are _sure_ that the check
was performed, use `HAVE_DECL_SYMBOL' in `#if':
#if !HAVE_DECL_SYMBOL
extern char *symbol;
#endif
If the test may have not been performed, however, because it is
safer _not_ to declare a symbol than to use a declaration that
conflicts with the system's one, you should use:
#if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC
void *malloc (size_t *s);
#endif
You fall into the second category only in extreme situations:
either your files may be used without being configured, or they
are used during the configuration. In most cases the traditional
approach is enough.
-- Macro: AC_CHECK_DECLS_ONCE (SYMBOLS)
For each of the SYMBOLS (_comma_-separated list), define
`HAVE_DECL_SYMBOL' (in all capitals) to `1' if SYMBOL is declared
in the default include files, otherwise to `0'. This is a
once-only variant of `AC_CHECK_DECLS'. It generates the checking
code at most once, so that `configure' is smaller and faster; but
the checks cannot be conditionalized and are always done once,
early during the `configure' run.

File: autoconf.info, Node: Structures, Next: Types, Prev: Declarations, Up: Existing Tests
5.8 Structures
==============
The following macros check for the presence of certain members in C
structures. If there is no macro specifically defined to check for a
member you need, then you can use the general structure-member macros
(*note Generic Structures::) or, for more complex tests, you may use
`AC_COMPILE_IFELSE' (*note Running the Compiler::).
* Menu:
* Particular Structures:: Macros to check for certain structure members
* Generic Structures:: How to find other structure members

File: autoconf.info, Node: Particular Structures, Next: Generic Structures, Up: Structures
5.8.1 Particular Structure Checks
---------------------------------
The following macros check for certain structures or structure members.
-- Macro: AC_STRUCT_DIRENT_D_INO
Perform all the actions of `AC_HEADER_DIRENT' (*note Particular
Headers::). Then, if `struct dirent' contains a `d_ino' member,
define `HAVE_STRUCT_DIRENT_D_INO'.
`HAVE_STRUCT_DIRENT_D_INO' indicates only the presence of `d_ino',
not whether its contents are always reliable. Traditionally, a
zero `d_ino' indicated a deleted directory entry, though current
systems hide this detail from the user and never return zero
`d_ino' values. Many current systems report an incorrect `d_ino'
for a directory entry that is a mount point.
-- Macro: AC_STRUCT_DIRENT_D_TYPE
Perform all the actions of `AC_HEADER_DIRENT' (*note Particular
Headers::). Then, if `struct dirent' contains a `d_type' member,
define `HAVE_STRUCT_DIRENT_D_TYPE'.
-- Macro: AC_STRUCT_ST_BLKSIZE
If `struct stat' contains an `st_blksize' member, define
`HAVE_STRUCT_STAT_ST_BLKSIZE'. The former name, `HAVE_ST_BLKSIZE'
is to be avoided, as its support will cease in the future. This
macro is obsoleted, and should be replaced by
AC_CHECK_MEMBERS([struct stat.st_blksize])
-- Macro: AC_STRUCT_ST_BLOCKS
If `struct stat' contains an `st_blocks' member, define
`HAVE_STRUCT_STAT_ST_BLOCKS'. Otherwise, require an `AC_LIBOBJ'
replacement of `fileblocks'. The former name, `HAVE_ST_BLOCKS' is
to be avoided, as its support will cease in the future.
-- Macro: AC_STRUCT_ST_RDEV
If `struct stat' contains an `st_rdev' member, define
`HAVE_STRUCT_STAT_ST_RDEV'. The former name for this macro,
`HAVE_ST_RDEV', is to be avoided as it will cease to be supported
in the future. Actually, even the new macro is obsolete and
should be replaced by:
AC_CHECK_MEMBERS([struct stat.st_rdev])
-- Macro: AC_STRUCT_TM
If `time.h' does not define `struct tm', define `TM_IN_SYS_TIME',
which means that including `sys/time.h' had better define `struct
tm'.
This macro is obsolescent, as `time.h' defines `struct tm' in
current systems. New programs need not use this macro.
-- Macro: AC_STRUCT_TIMEZONE
Figure out how to get the current timezone. If `struct tm' has a
`tm_zone' member, define `HAVE_STRUCT_TM_TM_ZONE' (and the
obsoleted `HAVE_TM_ZONE'). Otherwise, if the external array
`tzname' is found, define `HAVE_TZNAME'; if it is declared, define
`HAVE_DECL_TZNAME'.

File: autoconf.info, Node: Generic Structures, Prev: Particular Structures, Up: Structures
5.8.2 Generic Structure Checks
------------------------------
These macros are used to find structure members not covered by the
"particular" test macros.
-- Macro: AC_CHECK_MEMBER (AGGREGATE.MEMBER, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
Check whether MEMBER is a member of the aggregate AGGREGATE. If
no INCLUDES are specified, the default includes are used (*note
Default Includes::).
AC_CHECK_MEMBER([struct passwd.pw_gecos], [],
[AC_MSG_ERROR([We need `passwd.pw_gecos'!])],
[#include <pwd.h>])
You can use this macro for submembers:
AC_CHECK_MEMBER(struct top.middle.bot)
-- Macro: AC_CHECK_MEMBERS (MEMBERS, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
Check for the existence of each `AGGREGATE.MEMBER' of MEMBERS
using the previous macro. When MEMBER belongs to AGGREGATE,
define `HAVE_AGGREGATE_MEMBER' (in all capitals, with spaces and
dots replaced by underscores). If ACTION-IF-FOUND is given, it is
executed for each of the found members. If ACTION-IF-NOT-FOUND is
given, it is executed for each of the members that could not be
found.
This macro uses M4 lists:
AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize])

File: autoconf.info, Node: Types, Next: Compilers and Preprocessors, Prev: Structures, Up: Existing Tests
5.9 Types
=========
The following macros check for C types, either builtin or typedefs. If
there is no macro specifically defined to check for a type you need, and
you don't need to check for any special properties of it, then you can
use a general type-check macro.
* Menu:
* Particular Types:: Special handling to find certain types
* Generic Types:: How to find other types

File: autoconf.info, Node: Particular Types, Next: Generic Types, Up: Types
5.9.1 Particular Type Checks
----------------------------
These macros check for particular C types in `sys/types.h', `stdlib.h',
`stdint.h', `inttypes.h' and others, if they exist.
The Gnulib `stdint' module is an alternate way to define many of
these symbols; it is useful if you prefer your code to assume a
C99-or-better environment. *Note Gnulib::.
-- Macro: AC_TYPE_GETGROUPS
Define `GETGROUPS_T' to be whichever of `gid_t' or `int' is the
base type of the array argument to `getgroups'.
-- Macro: AC_TYPE_INT8_T
If `stdint.h' or `inttypes.h' defines the type `int8_t', define
`HAVE_INT8_T'. Otherwise, define `int8_t' to a signed integer
type that is exactly 8 bits wide and that uses two's complement
representation, if such a type exists.
-- Macro: AC_TYPE_INT16_T
This is like `AC_TYPE_INT8_T', except for 16-bit integers.
-- Macro: AC_TYPE_INT32_T
This is like `AC_TYPE_INT8_T', except for 32-bit integers.
-- Macro: AC_TYPE_INT64_T
This is like `AC_TYPE_INT8_T', except for 64-bit integers.
-- Macro: AC_TYPE_INTMAX_T
If `stdint.h' or `inttypes.h' defines the type `intmax_t', define
`HAVE_INTMAX_T'. Otherwise, define `intmax_t' to the widest
signed integer type.
-- Macro: AC_TYPE_INTPTR_T
If `stdint.h' or `inttypes.h' defines the type `intptr_t', define
`HAVE_INTPTR_T'. Otherwise, define `intptr_t' to a signed integer
type wide enough to hold a pointer, if such a type exists.
-- Macro: AC_TYPE_LONG_DOUBLE
If the C compiler supports a working `long double' type, define
`HAVE_LONG_DOUBLE'. The `long double' type might have the same
range and precision as `double'.
-- Macro: AC_TYPE_LONG_DOUBLE_WIDER
If the C compiler supports a working `long double' type with more
range or precision than the `double' type, define
`HAVE_LONG_DOUBLE_WIDER'.
-- Macro: AC_TYPE_LONG_LONG_INT
If the C compiler supports a working `long long int' type, define
`HAVE_LONG_LONG_INT'.
-- Macro: AC_TYPE_MBSTATE_T
Define `HAVE_MBSTATE_T' if `<wchar.h>' declares the `mbstate_t'
type. Also, define `mbstate_t' to be a type if `<wchar.h>' does
not declare it.
-- Macro: AC_TYPE_MODE_T
Define `mode_t' to a suitable type, if standard headers do not
define it.
-- Macro: AC_TYPE_OFF_T
Define `off_t' to a suitable type, if standard headers do not
define it.
-- Macro: AC_TYPE_PID_T
Define `pid_t' to a suitable type, if standard headers do not
define it.
-- Macro: AC_TYPE_SIGNAL
If `signal.h' declares `signal' as returning a pointer to a
function returning `void', define `RETSIGTYPE' to be `void';
otherwise, define it to be `int'.
Define signal handlers as returning type `RETSIGTYPE':
RETSIGTYPE
hup_handler ()
{
...
}
-- Macro: AC_TYPE_SIZE_T
Define `size_t' to a suitable type, if standard headers do not
define it.
-- Macro: AC_TYPE_SSIZE_T
Define `ssize_t' to a suitable type, if standard headers do not
define it.
-- Macro: AC_TYPE_UID_T
Define `uid_t' and `gid_t' to suitable types, if standard headers
do not define them.
-- Macro: AC_TYPE_UINT8_T
If `stdint.h' or `inttypes.h' defines the type `uint8_t', define
`HAVE_UINT8_T'. Otherwise, define `uint8_t' to an unsigned
integer type that is exactly 8 bits wide, if such a type exists.
-- Macro: AC_TYPE_UINT16_T
This is like `AC_TYPE_UINT8_T', except for 16-bit unsigned
integers.
-- Macro: AC_TYPE_UINT32_T
This is like `AC_TYPE_UINT8_T', except for 32-bit unsigned
integers.
-- Macro: AC_TYPE_UINT64_T
This is like `AC_TYPE_UINT8_T', except for 64-bit unsigned
integers.
-- Macro: AC_TYPE_UINTMAX_T
If `stdint.h' or `inttypes.h' defines the type `uintmax_t', define
`HAVE_UINTMAX_T'. Otherwise, define `uintmax_t' to the widest
unsigned integer type.
-- Macro: AC_TYPE_UINTPTR_T
If `stdint.h' or `inttypes.h' defines the type `uintptr_t', define
`HAVE_UINTPTR_T'. Otherwise, define `uintptr_t' to an unsigned
integer type wide enough to hold a pointer, if such a type exists.
-- Macro: AC_TYPE_UNSIGNED_LONG_LONG_INT
If the C compiler supports a working `unsigned long long int' type,
define `HAVE_UNSIGNED_LONG_LONG_INT'.

File: autoconf.info, Node: Generic Types, Prev: Particular Types, Up: Types
5.9.2 Generic Type Checks
-------------------------
These macros are used to check for types not covered by the "particular"
test macros.
-- Macro: AC_CHECK_TYPE (TYPE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
Check whether TYPE is defined. It may be a compiler builtin type
or defined by the INCLUDES (*note Default Includes::).
-- Macro: AC_CHECK_TYPES (TYPES, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
For each TYPE of the TYPES that is defined, define `HAVE_TYPE' (in
all capitals). If no INCLUDES are specified, the default includes
are used (*note Default Includes::). If ACTION-IF-FOUND is given,
it is additional shell code to execute when one of the types is
found. If ACTION-IF-NOT-FOUND is given, it is executed when one
of the types is not found.
This macro uses M4 lists:
AC_CHECK_TYPES([ptrdiff_t])
AC_CHECK_TYPES([unsigned long long int, uintmax_t])
Autoconf, up to 2.13, used to provide to another version of
`AC_CHECK_TYPE', broken by design. In order to keep backward
compatibility, a simple heuristics, quite safe but not totally, is
implemented. In case of doubt, read the documentation of the former
`AC_CHECK_TYPE', see *Note Obsolete Macros::.

File: autoconf.info, Node: Compilers and Preprocessors, Next: System Services, Prev: Types, Up: Existing Tests
5.10 Compilers and Preprocessors
================================
All the tests for compilers (`AC_PROG_CC', `AC_PROG_CXX',
`AC_PROG_F77') define the output variable `EXEEXT' based on the output
of the compiler, typically to the empty string if Posix and `.exe' if a
DOS variant.
They also define the output variable `OBJEXT' based on the output of
the compiler, after `.c' files have been excluded, typically to `o' if
Posix, `obj' if a DOS variant.
If the compiler being used does not produce executables, the tests
fail. If the executables can't be run, and cross-compilation is not
enabled, they fail too. *Note Manual Configuration::, for more on
support for cross compiling.
* Menu:
* Specific Compiler Characteristics:: Some portability issues
* Generic Compiler Characteristics:: Language independent tests and features
* C Compiler:: Checking its characteristics
* C++ Compiler:: Likewise
* Objective C Compiler:: Likewise
* Erlang Compiler and Interpreter:: Likewise
* Fortran Compiler:: Likewise

File: autoconf.info, Node: Specific Compiler Characteristics, Next: Generic Compiler Characteristics, Up: Compilers and Preprocessors
5.10.1 Specific Compiler Characteristics
----------------------------------------
Some compilers exhibit different behaviors.
Static/Dynamic Expressions
Autoconf relies on a trick to extract one bit of information from
the C compiler: using negative array sizes. For instance the
following excerpt of a C source demonstrates how to test whether
`int' objects are 4 bytes wide:
static int test_array[sizeof (int) == 4 ? 1 : -1];
To our knowledge, there is a single compiler that does not support
this trick: the HP C compilers (the real ones, not only the
"bundled") on HP-UX 11.00. They incorrectly reject the above
program with the diagnostic "Variable-length arrays cannot have
static storage." This bug comes from HP compilers' mishandling of
`sizeof (int)', not from the `? 1 : -1', and Autoconf works around
this problem by casting `sizeof (int)' to `long int' before
comparing it.

File: autoconf.info, Node: Generic Compiler Characteristics, Next: C Compiler, Prev: Specific Compiler Characteristics, Up: Compilers and Preprocessors
5.10.2 Generic Compiler Characteristics
---------------------------------------
-- Macro: AC_CHECK_SIZEOF (TYPE, [UNUSED], [INCLUDES =
`default-includes'])
Define `SIZEOF_TYPE' (*note Standard Symbols::) to be the size in
bytes of TYPE. If `type' is unknown, it gets a size of 0. If no
INCLUDES are specified, the default includes are used (*note
Default Includes::).
This macro now works even when cross-compiling. The UNUSED
argument was used when cross-compiling.
For example, the call
AC_CHECK_SIZEOF([int *])
defines `SIZEOF_INT_P' to be 8 on DEC Alpha AXP systems.
-- Macro: AC_CHECK_ALIGNOF (TYPE, [INCLUDES = `default-includes'])
Define `ALIGNOF_TYPE' (*note Standard Symbols::) to be the
alignment in bytes of TYPE. If `type' is unknown, it gets a size
of 0. If no INCLUDES are specified, the default includes are used
(*note Default Includes::).
-- Macro: AC_COMPUTE_INT (VAR, EXPRESSION, [INCLUDES =
`default-includes'], [ACTION-IF-FAILS])
Store into the shell variable VAR the value of the integer
EXPRESSION. The value should fit in an initializer in a C
variable of type `signed long'. To support cross compilation (in
which case, the macro only works on hosts that use twos-complement
arithmetic), it should be possible to evaluate the expression at
compile-time. If no INCLUDES are specified, the default includes
are used (*note Default Includes::).
Execute ACTION-IF-FAILS if the value cannot be determined
correctly.
-- Macro: AC_LANG_WERROR
Normally Autoconf ignores warnings generated by the compiler,
linker, and preprocessor. If this macro is used, warnings count
as fatal errors for the current language. This macro is useful
when the results of configuration are used where warnings are
unacceptable; for instance, if parts of a program are built with
the GCC `-Werror' option. If the whole program is built using
`-Werror' it is often simpler to put `-Werror' in the compiler
flags (`CFLAGS', etc.).

File: autoconf.info, Node: C Compiler, Next: C++ Compiler, Prev: Generic Compiler Characteristics, Up: Compilers and Preprocessors
5.10.3 C Compiler Characteristics
---------------------------------
The following macros provide ways to find and exercise a C Compiler.
There are a few constructs that ought to be avoided, but do not deserve
being checked for, since they can easily be worked around.
Don't use lines containing solitary backslashes
They tickle a bug in the HP-UX C compiler (checked on HP-UX 10.20,
11.00, and 11i). When given the following source:
#ifdef __STDC__
/\
* A comment with backslash-newlines in it. %{ %} *\
\
/
char str[] = "\\
" A string with backslash-newlines in it %{ %} \\
"";
char apostrophe = '\\
\
'\
';
#endif
the compiler incorrectly fails with the diagnostics
"Non-terminating comment at end of file" and "Missing `#endif' at
end of file." Removing the lines with solitary backslashes solves
the problem.
Don't compile several files at once if output matters to you
Some compilers, such as HP's, report names of files being compiled
when given more than one file operand. For instance:
$ cc a.c b.c
a.c:
b.c:
This can cause problems if you observe the output of the compiler
to detect failures. Invoking `cc -c a.c && cc -c b.c && cc -o c
a.o b.o' solves the issue.
Don't rely on `#error' failing
The IRIX C compiler does not fail when #error is preprocessed; it
simply emits a diagnostic and continues, exiting successfully. So,
instead of an error directive like `#error "Unsupported word size"'
it is more portable to use an invalid directive like `#Unsupported
word size' in Autoconf tests. In ordinary source code, `#error' is
OK, since installers with inadequate compilers like IRIX can simply
examine these compilers' diagnostic output.
Don't rely on correct `#line' support
On Solaris, `c89' (at least Sun C 5.3 through 5.8) diagnoses
`#line' directives whose line numbers are greater than 32767.
Nothing in Posix makes this invalid. That is why Autoconf stopped
issuing `#line' directives.
-- Macro: AC_PROG_CC ([COMPILER-SEARCH-LIST])
Determine a C compiler to use. If `CC' is not already set in the
environment, check for `gcc' and `cc', then for other C compilers.
Set output variable `CC' to the name of the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of C compilers
to search for. This just gives the user an opportunity to specify
an alternative search list for the C compiler. For example, if
you didn't like the default order, then you could invoke
`AC_PROG_CC' like this:
AC_PROG_CC([gcc cl cc])
If the C compiler does not handle function prototypes correctly by
default, try to add an option to output variable `CC' to make it
so. This macro tries various options that select
standard-conformance modes on various systems.
After calling this macro you can check whether the C compiler has
been set to accept ANSI C89 (ISO C90); if not, the shell variable
`ac_cv_prog_cc_c89' is set to `no'. See also `AC_C_PROTOTYPES'
below.
If using the GNU C compiler, set shell variable `GCC' to `yes'.
If output variable `CFLAGS' was not already set, set it to `-g
-O2' for the GNU C compiler (`-O2' on systems where GCC does not
accept `-g'), or `-g' for other compilers.
-- Macro: AC_PROG_CC_C_O
If the C compiler does not accept the `-c' and `-o' options
simultaneously, define `NO_MINUS_C_MINUS_O'. This macro actually
tests both the compiler found by `AC_PROG_CC', and, if different,
the first `cc' in the path. The test fails if one fails. This
macro was created for GNU Make to choose the default C compilation
rule.
-- Macro: AC_PROG_CPP
Set output variable `CPP' to a command that runs the C
preprocessor. If `$CC -E' doesn't work, `/lib/cpp' is used. It
is only portable to run `CPP' on files with a `.c' extension.
Some preprocessors don't indicate missing include files by the
error status. For such preprocessors an internal variable is set
that causes other macros to check the standard error from the
preprocessor and consider the test failed if any warnings have
been reported. For most preprocessors, though, warnings do not
cause include-file tests to fail unless `AC_PROG_CPP_WERROR' is
also specified.
-- Macro: AC_PROG_CPP_WERROR
This acts like `AC_PROG_CPP', except it treats warnings from the
preprocessor as errors even if the preprocessor exit status
indicates success. This is useful for avoiding headers that
generate mandatory warnings, such as deprecation notices.
The following macros check for C compiler or machine architecture
features. To check for characteristics not listed here, use
`AC_COMPILE_IFELSE' (*note Running the Compiler::) or `AC_RUN_IFELSE'
(*note Runtime::).
-- Macro: AC_PROG_CC_STDC
If the C compiler cannot compile ISO Standard C (currently C99),
try to add an option to output variable `CC' to make it work. If
the compiler does not support C99, fall back to supporting ANSI
C89 (ISO C90).
After calling this macro you can check whether the C compiler has
been set to accept Standard C; if not, the shell variable
`ac_cv_prog_cc_stdc' is set to `no'.
-- Macro: AC_PROG_CC_C89
If the C compiler is not in ANSI C89 (ISO C90) mode by default,
try to add an option to output variable `CC' to make it so. This
macro tries various options that select ANSI C89 on some system or
another. It considers the compiler to be in ANSI C89 mode if it
handles function prototypes correctly.
After calling this macro you can check whether the C compiler has
been set to accept ANSI C89; if not, the shell variable
`ac_cv_prog_cc_c89' is set to `no'.
This macro is called automatically by `AC_PROG_CC'.
-- Macro: AC_PROG_CC_C99
If the C compiler is not in C99 mode by default, try to add an
option to output variable `CC' to make it so. This macro tries
various options that select C99 on some system or another. It
considers the compiler to be in C99 mode if it handles `_Bool',
`//' comments, flexible array members, `inline', `long long int',
mixed code and declarations, named initialization of structs,
`restrict', `va_copy', varargs macros, variable declarations in
`for' loops, and variable length arrays.
After calling this macro you can check whether the C compiler has
been set to accept C99; if not, the shell variable
`ac_cv_prog_cc_c99' is set to `no'.
-- Macro: AC_C_BACKSLASH_A
Define `HAVE_C_BACKSLASH_A' to 1 if the C compiler understands
`\a'.
This macro is obsolescent, as current C compilers understand `\a'.
New programs need not use this macro.
-- Macro: AC_C_BIGENDIAN ([ACTION-IF-TRUE], [ACTION-IF-FALSE],
[ACTION-IF-UNKNOWN])
If words are stored with the most significant byte first (like
Motorola and SPARC CPUs), execute ACTION-IF-TRUE. If words are
stored with the least significant byte first (like Intel and VAX
CPUs), execute ACTION-IF-FALSE.
This macro runs a test-case if endianness cannot be determined
from the system header files. When cross-compiling, the test-case
is not run but grep'ed for some magic values. ACTION-IF-UNKNOWN
is executed if the latter case fails to determine the byte sex of
the host system.
The default for ACTION-IF-TRUE is to define `WORDS_BIGENDIAN'.
The default for ACTION-IF-FALSE is to do nothing. And finally,
the default for ACTION-IF-UNKNOWN is to abort configure and tell
the installer which variable he should preset to bypass this test.
-- Macro: AC_C_CONST
If the C compiler does not fully support the `const' keyword,
define `const' to be empty. Some C compilers that do not define
`__STDC__' do support `const'; some compilers that define
`__STDC__' do not completely support `const'. Programs can simply
use `const' as if every C compiler supported it; for those that
don't, the makefile or configuration header file defines it as
empty.
Occasionally installers use a C++ compiler to compile C code,
typically because they lack a C compiler. This causes problems
with `const', because C and C++ treat `const' differently. For
example:
const int foo;
is valid in C but not in C++. These differences unfortunately
cannot be papered over by defining `const' to be empty.
If `autoconf' detects this situation, it leaves `const' alone, as
this generally yields better results in practice. However, using a
C++ compiler to compile C code is not recommended or supported, and
installers who run into trouble in this area should get a C
compiler like GCC to compile their C code.
This macro is obsolescent, as current C compilers support `const'.
New programs need not use this macro.
-- Macro: AC_C_RESTRICT
If the C compiler recognizes the `restrict' keyword, don't do
anything. If it recognizes only a variant spelling (`__restrict',
`__restrict__', or `_Restrict'), then define `restrict' to that.
Otherwise, define `restrict' to be empty. Thus, programs may
simply use `restrict' as if every C compiler supported it; for
those that do not, the makefile or configuration header defines it
away.
Although support in C++ for the `restrict' keyword is not
required, several C++ compilers do accept the keyword. This macro
works for them, too.
-- Macro: AC_C_VOLATILE
If the C compiler does not understand the keyword `volatile',
define `volatile' to be empty. Programs can simply use `volatile'
as if every C compiler supported it; for those that do not, the
makefile or configuration header defines it as empty.
If the correctness of your program depends on the semantics of
`volatile', simply defining it to be empty does, in a sense, break
your code. However, given that the compiler does not support
`volatile', you are at its mercy anyway. At least your program
compiles, when it wouldn't before. *Note Volatile Objects::, for
more about `volatile'.
In general, the `volatile' keyword is a standard C feature, so you
might expect that `volatile' is available only when `__STDC__' is
defined. However, Ultrix 4.3's native compiler does support
volatile, but does not define `__STDC__'.
This macro is obsolescent, as current C compilers support
`volatile'. New programs need not use this macro.
-- Macro: AC_C_INLINE
If the C compiler supports the keyword `inline', do nothing.
Otherwise define `inline' to `__inline__' or `__inline' if it
accepts one of those, otherwise define `inline' to be empty.
-- Macro: AC_C_CHAR_UNSIGNED
If the C type `char' is unsigned, define `__CHAR_UNSIGNED__',
unless the C compiler predefines it.
-- Macro: AC_C_STRINGIZE
If the C preprocessor supports the stringizing operator, define
`HAVE_STRINGIZE'. The stringizing operator is `#' and is found in
macros such as this:
#define x(y) #y
This macro is obsolescent, as current C compilers support the
stringizing operator. New programs need not use this macro.
-- Macro: AC_C_FLEXIBLE_ARRAY_MEMBER
If the C compiler supports flexible array members, define
`FLEXIBLE_ARRAY_MEMBER' to nothing; otherwise define it to 1.
That way, a declaration like this:
struct s
{
size_t n_vals;
double val[FLEXIBLE_ARRAY_MEMBER];
};
will let applications use the "struct hack" even with compilers
that do not support flexible array members. To allocate and use
such an object, you can use code like this:
size_t i;
size_t n = compute_value_count ();
struct s *p =
malloc (offsetof (struct s, val)
+ n * sizeof (double));
p->n_vals = n;
for (i = 0; i < n; i++)
p->val[i] = compute_value (i);
-- Macro: AC_C_VARARRAYS
If the C compiler supports variable-length arrays, define
`HAVE_C_VARRAYS'. A variable-length array is an array of automatic
storage duration whose length is determined at run time, when the
array is declared.
-- Macro: AC_C_TYPEOF
If the C compiler supports GCC's `typeof' syntax either directly or
through a different spelling of the keyword (e.g., `__typeof__'),
define `HAVE_TYPEOF'. If the support is available only through a
different spelling, define `typeof' to that spelling.
-- Macro: AC_C_PROTOTYPES
If function prototypes are understood by the compiler (as
determined by `AC_PROG_CC'), define `PROTOTYPES' and
`__PROTOTYPES'. Defining `__PROTOTYPES' is for the benefit of
header files that cannot use macros that infringe on user name
space.
This macro is obsolescent, as current C compilers support
prototypes. New programs need not use this macro.
-- Macro: AC_PROG_GCC_TRADITIONAL
Add `-traditional' to output variable `CC' if using the GNU C
compiler and `ioctl' does not work properly without
`-traditional'. That usually happens when the fixed header files
have not been installed on an old system.
This macro is obsolescent, since current versions of the GNU C
compiler fix the header files automatically when installed.

File: autoconf.info, Node: C++ Compiler, Next: Objective C Compiler, Prev: C Compiler, Up: Compilers and Preprocessors
5.10.4 C++ Compiler Characteristics
-----------------------------------
-- Macro: AC_PROG_CXX ([COMPILER-SEARCH-LIST])
Determine a C++ compiler to use. Check whether the environment
variable `CXX' or `CCC' (in that order) is set; if so, then set
output variable `CXX' to its value.
Otherwise, if the macro is invoked without an argument, then
search for a C++ compiler under the likely names (first `g++' and
`c++' then other names). If none of those checks succeed, then as
a last resort set `CXX' to `g++'.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of C++
compilers to search for. This just gives the user an opportunity
to specify an alternative search list for the C++ compiler. For
example, if you didn't like the default order, then you could
invoke `AC_PROG_CXX' like this:
AC_PROG_CXX([gcc cl KCC CC cxx cc++ xlC aCC c++ g++])
If using the GNU C++ compiler, set shell variable `GXX' to `yes'.
If output variable `CXXFLAGS' was not already set, set it to `-g
-O2' for the GNU C++ compiler (`-O2' on systems where G++ does not
accept `-g'), or `-g' for other compilers.
-- Macro: AC_PROG_CXXCPP
Set output variable `CXXCPP' to a command that runs the C++
preprocessor. If `$CXX -E' doesn't work, `/lib/cpp' is used. It
is portable to run `CXXCPP' only on files with a `.c', `.C',
`.cc', or `.cpp' extension.
Some preprocessors don't indicate missing include files by the
error status. For such preprocessors an internal variable is set
that causes other macros to check the standard error from the
preprocessor and consider the test failed if any warnings have
been reported. However, it is not known whether such broken
preprocessors exist for C++.
-- Macro: AC_PROG_CXX_C_O
Test whether the C++ compiler accepts the options `-c' and `-o'
simultaneously, and define `CXX_NO_MINUS_C_MINUS_O', if it does
not.

File: autoconf.info, Node: Objective C Compiler, Next: Erlang Compiler and Interpreter, Prev: C++ Compiler, Up: Compilers and Preprocessors
5.10.5 Objective C Compiler Characteristics
-------------------------------------------
-- Macro: AC_PROG_OBJC ([COMPILER-SEARCH-LIST])
Determine an Objective C compiler to use. If `OBJC' is not already
set in the environment, check for Objective C compilers. Set
output variable `OBJC' to the name of the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of Objective C
compilers to search for. This just gives the user an opportunity
to specify an alternative search list for the Objective C
compiler. For example, if you didn't like the default order, then
you could invoke `AC_PROG_OBJC' like this:
AC_PROG_OBJC([gcc objcc objc])
If using the GNU Objective C compiler, set shell variable `GOBJC'
to `yes'. If output variable `OBJCFLAGS' was not already set, set
it to `-g -O2' for the GNU Objective C compiler (`-O2' on systems
where `gcc' does not accept `-g'), or `-g' for other compilers.
-- Macro: AC_PROG_OBJCCPP
Set output variable `OBJCCPP' to a command that runs the Objective
C preprocessor. If `$OBJC -E' doesn't work, `/lib/cpp' is used.

File: autoconf.info, Node: Erlang Compiler and Interpreter, Next: Fortran Compiler, Prev: Objective C Compiler, Up: Compilers and Preprocessors
5.10.6 Erlang Compiler and Interpreter Characteristics
------------------------------------------------------
Autoconf defines the following macros for determining paths to the
essential Erlang/OTP programs:
-- Macro: AC_ERLANG_PATH_ERLC ([VALUE-IF-NOT-FOUND], [PATH])
Determine an Erlang compiler to use. If `ERLC' is not already set
in the environment, check for `erlc'. Set output variable `ERLC'
to the complete path of the compiler command found. In addition,
if `ERLCFLAGS' is not set in the environment, set it to an empty
value.
The two optional arguments have the same meaning as the two last
arguments of macro `AC_PROG_PATH' for looking for the `erlc'
program. For example, to look for `erlc' only in the
`/usr/lib/erlang/bin' directory:
AC_ERLANG_PATH_ERLC([not found], [/usr/lib/erlang/bin])
-- Macro: AC_ERLANG_NEED_ERLC ([PATH])
A simplified variant of the `AC_ERLANG_PATH_ERLC' macro, that
prints an error message and exits the `configure' script if the
`erlc' program is not found.
-- Macro: AC_ERLANG_PATH_ERL ([VALUE-IF-NOT-FOUND], [PATH])
Determine an Erlang interpreter to use. If `ERL' is not already
set in the environment, check for `erl'. Set output variable
`ERL' to the complete path of the interpreter command found.
The two optional arguments have the same meaning as the two last
arguments of macro `AC_PROG_PATH' for looking for the `erl'
program. For example, to look for `erl' only in the
`/usr/lib/erlang/bin' directory:
AC_ERLANG_PATH_ERL([not found], [/usr/lib/erlang/bin])
-- Macro: AC_ERLANG_NEED_ERL ([PATH])
A simplified variant of the `AC_ERLANG_PATH_ERL' macro, that
prints an error message and exits the `configure' script if the
`erl' program is not found.

File: autoconf.info, Node: Fortran Compiler, Prev: Erlang Compiler and Interpreter, Up: Compilers and Preprocessors
5.10.7 Fortran Compiler Characteristics
---------------------------------------
The Autoconf Fortran support is divided into two categories: legacy
Fortran 77 macros (`F77'), and modern Fortran macros (`FC'). The
former are intended for traditional Fortran 77 code, and have output
variables like `F77', `FFLAGS', and `FLIBS'. The latter are for newer
programs that can (or must) compile under the newer Fortran standards,
and have output variables like `FC', `FCFLAGS', and `FCLIBS'.
Except for two new macros `AC_FC_SRCEXT' and `AC_FC_FREEFORM' (see
below), the `FC' and `F77' macros behave almost identically, and so
they are documented together in this section.
-- Macro: AC_PROG_F77 ([COMPILER-SEARCH-LIST])
Determine a Fortran 77 compiler to use. If `F77' is not already
set in the environment, then check for `g77' and `f77', and then
some other names. Set the output variable `F77' to the name of
the compiler found.
This macro may, however, be invoked with an optional first argument
which, if specified, must be a blank-separated list of Fortran 77
compilers to search for. This just gives the user an opportunity
to specify an alternative search list for the Fortran 77 compiler.
For example, if you didn't like the default order, then you could
invoke `AC_PROG_F77' like this:
AC_PROG_F77([fl32 f77 fort77 xlf g77 f90 xlf90])
If using `g77' (the GNU Fortran 77 compiler), then set the shell
variable `G77' to `yes'. If the output variable `FFLAGS' was not
already set in the environment, then set it to `-g -02' for `g77'
(or `-O2' where `g77' does not accept `-g'). Otherwise, set
`FFLAGS' to `-g' for all other Fortran 77 compilers.
-- Macro: AC_PROG_FC ([COMPILER-SEARCH-LIST], [DIALECT])
Determine a Fortran compiler to use. If `FC' is not already set in
the environment, then `dialect' is a hint to indicate what Fortran
dialect to search for; the default is to search for the newest
available dialect. Set the output variable `FC' to the name of
the compiler found.
By default, newer dialects are preferred over older dialects, but
if `dialect' is specified then older dialects are preferred
starting with the specified dialect. `dialect' can currently be
one of Fortran 77, Fortran 90, or Fortran 95. However, this is
only a hint of which compiler _name_ to prefer (e.g., `f90' or
`f95'), and no attempt is made to guarantee that a particular
language standard is actually supported. Thus, it is preferable
that you avoid the `dialect' option, and use AC_PROG_FC only for
code compatible with the latest Fortran standard.
This macro may, alternatively, be invoked with an optional first
argument which, if specified, must be a blank-separated list of
Fortran compilers to search for, just as in `AC_PROG_F77'.
If the output variable `FCFLAGS' was not already set in the
environment, then set it to `-g -02' for GNU `g77' (or `-O2' where
`g77' does not accept `-g'). Otherwise, set `FCFLAGS' to `-g' for
all other Fortran compilers.
-- Macro: AC_PROG_F77_C_O
-- Macro: AC_PROG_FC_C_O
Test whether the Fortran compiler accepts the options `-c' and
`-o' simultaneously, and define `F77_NO_MINUS_C_MINUS_O' or
`FC_NO_MINUS_C_MINUS_O', respectively, if it does not.
The following macros check for Fortran compiler characteristics. To
check for characteristics not listed here, use `AC_COMPILE_IFELSE'
(*note Running the Compiler::) or `AC_RUN_IFELSE' (*note Runtime::),
making sure to first set the current language to Fortran 77 or Fortran
via `AC_LANG([Fortran 77])' or `AC_LANG(Fortran)' (*note Language
Choice::).
-- Macro: AC_F77_LIBRARY_LDFLAGS
-- Macro: AC_FC_LIBRARY_LDFLAGS
Determine the linker flags (e.g., `-L' and `-l') for the "Fortran
intrinsic and runtime libraries" that are required to successfully
link a Fortran program or shared library. The output variable
`FLIBS' or `FCLIBS' is set to these flags (which should be
included after `LIBS' when linking).
This macro is intended to be used in those situations when it is
necessary to mix, e.g., C++ and Fortran source code in a single
program or shared library (*note Mixing Fortran 77 With C and C++:
(automake)Mixing Fortran 77 With C and C++.).
For example, if object files from a C++ and Fortran compiler must
be linked together, then the C++ compiler/linker must be used for
linking (since special C++-ish things need to happen at link time
like calling global constructors, instantiating templates,
enabling exception support, etc.).
However, the Fortran intrinsic and runtime libraries must be
linked in as well, but the C++ compiler/linker doesn't know by
default how to add these Fortran 77 libraries. Hence, this macro
was created to determine these Fortran libraries.
The macros `AC_F77_DUMMY_MAIN' and `AC_FC_DUMMY_MAIN' or
`AC_F77_MAIN' and `AC_FC_MAIN' are probably also necessary to link
C/C++ with Fortran; see below.
-- Macro: AC_F77_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
-- Macro: AC_FC_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
With many compilers, the Fortran libraries detected by
`AC_F77_LIBRARY_LDFLAGS' or `AC_FC_LIBRARY_LDFLAGS' provide their
own `main' entry function that initializes things like Fortran
I/O, and which then calls a user-provided entry function named
(say) `MAIN__' to run the user's program. The `AC_F77_DUMMY_MAIN'
and `AC_FC_DUMMY_MAIN' or `AC_F77_MAIN' and `AC_FC_MAIN' macros
figure out how to deal with this interaction.
When using Fortran for purely numerical functions (no I/O, etc.)
often one prefers to provide one's own `main' and skip the Fortran
library initializations. In this case, however, one may still
need to provide a dummy `MAIN__' routine in order to prevent
linking errors on some systems. `AC_F77_DUMMY_MAIN' or
`AC_FC_DUMMY_MAIN' detects whether any such routine is _required_
for linking, and what its name is; the shell variable
`F77_DUMMY_MAIN' or `FC_DUMMY_MAIN' holds this name, `unknown'
when no solution was found, and `none' when no such dummy main is
needed.
By default, ACTION-IF-FOUND defines `F77_DUMMY_MAIN' or
`FC_DUMMY_MAIN' to the name of this routine (e.g., `MAIN__') _if_
it is required. ACTION-IF-NOT-FOUND defaults to exiting with an
error.
In order to link with Fortran routines, the user's C/C++ program
should then include the following code to define the dummy main if
it is needed:
#ifdef F77_DUMMY_MAIN
# ifdef __cplusplus
extern "C"
# endif
int F77_DUMMY_MAIN() { return 1; }
#endif
(Replace `F77' with `FC' for Fortran instead of Fortran 77.)
Note that this macro is called automatically from `AC_F77_WRAPPERS'
or `AC_FC_WRAPPERS'; there is generally no need to call it
explicitly unless one wants to change the default actions.
-- Macro: AC_F77_MAIN
-- Macro: AC_FC_MAIN
As discussed above, many Fortran libraries allow you to provide an
entry point called (say) `MAIN__' instead of the usual `main',
which is then called by a `main' function in the Fortran libraries
that initializes things like Fortran I/O. The `AC_F77_MAIN' and
`AC_FC_MAIN' macros detect whether it is _possible_ to utilize
such an alternate main function, and defines `F77_MAIN' and
`FC_MAIN' to the name of the function. (If no alternate main
function name is found, `F77_MAIN' and `FC_MAIN' are simply
defined to `main'.)
Thus, when calling Fortran routines from C that perform things
like I/O, one should use this macro and name the "main" function
`F77_MAIN' or `FC_MAIN' instead of `main'.
-- Macro: AC_F77_WRAPPERS
-- Macro: AC_FC_WRAPPERS
Defines C macros `F77_FUNC (name, NAME)', `FC_FUNC (name, NAME)',
`F77_FUNC_(name, NAME)', and `FC_FUNC_(name, NAME)' to properly
mangle the names of C/C++ identifiers, and identifiers with
underscores, respectively, so that they match the name-mangling
scheme used by the Fortran compiler.
Fortran is case-insensitive, and in order to achieve this the
Fortran compiler converts all identifiers into a canonical case
and format. To call a Fortran subroutine from C or to write a C
function that is callable from Fortran, the C program must
explicitly use identifiers in the format expected by the Fortran
compiler. In order to do this, one simply wraps all C identifiers
in one of the macros provided by `AC_F77_WRAPPERS' or
`AC_FC_WRAPPERS'. For example, suppose you have the following
Fortran 77 subroutine:
subroutine foobar (x, y)
double precision x, y
y = 3.14159 * x
return
end
You would then declare its prototype in C or C++ as:
#define FOOBAR_F77 F77_FUNC (foobar, FOOBAR)
#ifdef __cplusplus
extern "C" /* prevent C++ name mangling */
#endif
void FOOBAR_F77(double *x, double *y);
Note that we pass both the lowercase and uppercase versions of the
function name to `F77_FUNC' so that it can select the right one.
Note also that all parameters to Fortran 77 routines are passed as
pointers (*note Mixing Fortran 77 With C and C++: (automake)Mixing
Fortran 77 With C and C++.).
(Replace `F77' with `FC' for Fortran instead of Fortran 77.)
Although Autoconf tries to be intelligent about detecting the
name-mangling scheme of the Fortran compiler, there may be Fortran
compilers that it doesn't support yet. In this case, the above
code generates a compile-time error, but some other behavior
(e.g., disabling Fortran-related features) can be induced by
checking whether `F77_FUNC' or `FC_FUNC' is defined.
Now, to call that routine from a C program, we would do something
like:
{
double x = 2.7183, y;
FOOBAR_F77 (&x, &y);
}
If the Fortran identifier contains an underscore (e.g., `foo_bar'),
you should use `F77_FUNC_' or `FC_FUNC_' instead of `F77_FUNC' or
`FC_FUNC' (with the same arguments). This is because some Fortran
compilers mangle names differently if they contain an underscore.
-- Macro: AC_F77_FUNC (NAME, [SHELLVAR])
-- Macro: AC_FC_FUNC (NAME, [SHELLVAR])
Given an identifier NAME, set the shell variable SHELLVAR to hold
the mangled version NAME according to the rules of the Fortran
linker (see also `AC_F77_WRAPPERS' or `AC_FC_WRAPPERS'). SHELLVAR
is optional; if it is not supplied, the shell variable is simply
NAME. The purpose of this macro is to give the caller a way to
access the name-mangling information other than through the C
preprocessor as above, for example, to call Fortran routines from
some language other than C/C++.
-- Macro: AC_FC_SRCEXT (EXT, [ACTION-IF-SUCCESS], [ACTION-IF-FAILURE])
By default, the `FC' macros perform their tests using a `.f'
extension for source-code files. Some compilers, however, only
enable newer language features for appropriately named files,
e.g., Fortran 90 features only for `.f90' files. On the other
hand, some other compilers expect all source files to end in `.f'
and require special flags to support other file name extensions.
The `AC_FC_SRCEXT' macro deals with both of these issues.
The `AC_FC_SRCEXT' tries to get the `FC' compiler to accept files
ending with the extension .EXT (i.e., EXT does _not_ contain the
dot). If any special compiler flags are needed for this, it
stores them in the output variable `FCFLAGS_'EXT. This extension
and these flags are then used for all subsequent `FC' tests (until
`AC_FC_SRCEXT' is called again).
For example, you would use `AC_FC_SRCEXT(f90)' to employ the
`.f90' extension in future tests, and it would set a `FCFLAGS_f90'
output variable with any extra flags that are needed to compile
such files.
The `FCFLAGS_'EXT can _not_ be simply absorbed into `FCFLAGS', for
two reasons based on the limitations of some compilers. First,
only one `FCFLAGS_'EXT can be used at a time, so files with
different extensions must be compiled separately. Second,
`FCFLAGS_'EXT must appear _immediately_ before the source-code
file name when compiling. So, continuing the example above, you
might compile a `foo.f90' file in your makefile with the command:
foo.o: foo.f90
$(FC) -c $(FCFLAGS) $(FCFLAGS_f90) '$(srcdir)/foo.f90'
If `AC_FC_SRCEXT' succeeds in compiling files with the EXT
extension, it calls ACTION-IF-SUCCESS (defaults to nothing). If
it fails, and cannot find a way to make the `FC' compiler accept
such files, it calls ACTION-IF-FAILURE (defaults to exiting with an
error message).
-- Macro: AC_FC_FREEFORM ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE])
The `AC_FC_FREEFORM' tries to ensure that the Fortran compiler
(`$FC') allows free-format source code (as opposed to the older
fixed-format style from Fortran 77). If necessary, it may add some
additional flags to `FCFLAGS'.
This macro is most important if you are using the default `.f'
extension, since many compilers interpret this extension as
indicating fixed-format source unless an additional flag is
supplied. If you specify a different extension with
`AC_FC_SRCEXT', such as `.f90' or `.f95', then `AC_FC_FREEFORM'
ordinarily succeeds without modifying `FCFLAGS'.
If `AC_FC_FREEFORM' succeeds in compiling free-form source, it
calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it
calls ACTION-IF-FAILURE (defaults to exiting with an error
message).

File: autoconf.info, Node: System Services, Next: Posix Variants, Prev: Compilers and Preprocessors, Up: Existing Tests
5.11 System Services
====================
The following macros check for operating system services or
capabilities.
-- Macro: AC_PATH_X
Try to locate the X Window System include files and libraries. If
the user gave the command line options `--x-includes=DIR' and
`--x-libraries=DIR', use those directories.
If either or both were not given, get the missing values by running
`xmkmf' (or an executable pointed to by the `XMKMF' environment
variable) on a trivial `Imakefile' and examining the makefile that
it produces. Setting `XMKMF' to `false' disables this method.
If this method fails to find the X Window System, `configure'
looks for the files in several directories where they often reside.
If either method is successful, set the shell variables
`x_includes' and `x_libraries' to their locations, unless they are
in directories the compiler searches by default.
If both methods fail, or the user gave the command line option
`--without-x', set the shell variable `no_x' to `yes'; otherwise
set it to the empty string.
-- Macro: AC_PATH_XTRA
An enhanced version of `AC_PATH_X'. It adds the C compiler flags
that X needs to output variable `X_CFLAGS', and the X linker flags
to `X_LIBS'. Define `X_DISPLAY_MISSING' if X is not available.
This macro also checks for special libraries that some systems
need in order to compile X programs. It adds any that the system
needs to output variable `X_EXTRA_LIBS'. And it checks for
special X11R6 libraries that need to be linked with before
`-lX11', and adds any found to the output variable `X_PRE_LIBS'.
-- Macro: AC_SYS_INTERPRETER
Check whether the system supports starting scripts with a line of
the form `#!/bin/sh' to select the interpreter to use for the
script. After running this macro, shell code in `configure.ac'
can check the shell variable `interpval'; it is set to `yes' if
the system supports `#!', `no' if not.
-- Macro: AC_SYS_LARGEFILE
Arrange for large-file support
(http://www.unix-systems.org/version2/whatsnew/lfs20mar.html). On
some hosts, one must use special compiler options to build
programs that can access large files. Append any such options to
the output variable `CC'. Define `_FILE_OFFSET_BITS' and
`_LARGE_FILES' if necessary.
Large-file support can be disabled by configuring with the
`--disable-largefile' option.
If you use this macro, check that your program works even when
`off_t' is wider than `long int', since this is common when
large-file support is enabled. For example, it is not correct to
print an arbitrary `off_t' value `X' with `printf ("%ld", (long
int) X)'.
The LFS introduced the `fseeko' and `ftello' functions to replace
their C counterparts `fseek' and `ftell' that do not use `off_t'.
Take care to use `AC_FUNC_FSEEKO' to make their prototypes
available when using them and large-file support is enabled.
-- Macro: AC_SYS_LONG_FILE_NAMES
If the system supports file names longer than 14 characters, define
`HAVE_LONG_FILE_NAMES'.
-- Macro: AC_SYS_POSIX_TERMIOS
Check to see if the Posix termios headers and functions are
available on the system. If so, set the shell variable
`ac_cv_sys_posix_termios' to `yes'. If not, set the variable to
`no'.

File: autoconf.info, Node: Posix Variants, Next: Erlang Libraries, Prev: System Services, Up: Existing Tests
5.12 Posix Variants
===================
The following macros check for certain operating systems that need
special treatment for some programs, due to exceptional oddities in
their header files or libraries. These macros are warts; they will be
replaced by a more systematic approach, based on the functions they make
available or the environments they provide.
-- Macro: AC_AIX
If on AIX, define `_ALL_SOURCE'. Allows the use of some BSD
functions. Should be called before any macros that run the C
compiler.
-- Macro: AC_GNU_SOURCE
If using the GNU C library, define `_GNU_SOURCE'. Allows the use
of some GNU functions. Should be called before any macros that
run the C compiler.
-- Macro: AC_ISC_POSIX
For INTERACTIVE Systems Corporation Unix, add `-lcposix' to output
variable `LIBS' if necessary for Posix facilities. Call this
after `AC_PROG_CC' and before any other macros that use Posix
interfaces.
This macro is obsolescent, as INTERACTIVE Unix is obsolete, and Sun
dropped support for it on 2006-07-23. New programs need not use
this macro.
-- Macro: AC_MINIX
If on Minix, define `_MINIX' and `_POSIX_SOURCE' and define
`_POSIX_1_SOURCE' to be 2. This allows the use of Posix
facilities. Should be called before any macros that run the C
compiler.
-- Macro: AC_USE_SYSTEM_EXTENSIONS
If possible, enable extensions to Posix on hosts that normally
disable the extensions, typically due to standards-conformance
namespace issues. This may involve defining `__EXTENSIONS__' and
`_POSIX_PTHREAD_SEMANTICS', which are macros used by Solaris. It
also defines `_TANDEM_SOURCE' for the HP NonStop platform. This
macro also has the combined effects of `AC_GNU_SOURCE', `AC_AIX',
and `AC_MINIX'.

File: autoconf.info, Node: Erlang Libraries, Prev: Posix Variants, Up: Existing Tests
5.13 Erlang Libraries
=====================
The following macros check for an installation of Erlang/OTP, and for
the presence of certain Erlang libraries. All those macros require the
configuration of an Erlang interpreter and an Erlang compiler (*note
Erlang Compiler and Interpreter::).
-- Macro: AC_ERLANG_SUBST_ROOT_DIR
Set the output variable `ERLANG_ROOT_DIR' to the path to the base
directory in which Erlang/OTP is installed (as returned by
Erlang's `code:root_dir/0' function). The result of this test is
cached if caching is enabled when running `configure'.
-- Macro: AC_ERLANG_SUBST_LIB_DIR
Set the output variable `ERLANG_LIB_DIR' to the path of the library
directory of Erlang/OTP (as returned by Erlang's `code:lib_dir/0'
function), which subdirectories each contain an installed
Erlang/OTP library. The result of this test is cached if caching
is enabled when running `configure'.
-- Macro: AC_ERLANG_CHECK_LIB (LIBRARY, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Test whether the Erlang/OTP library LIBRARY is installed by
calling Erlang's `code:lib_dir/1' function. The result of this
test is cached if caching is enabled when running `configure'.
ACTION-IF-FOUND is a list of shell commands to run if the library
is installed; ACTION-IF-NOT-FOUND is a list of shell commands to
run if it is not. Additionally, if the library is installed, the
output variable `ERLANG_LIB_DIR_LIBRARY' is set to the path to the
library installation directory, and the output variable
`ERLANG_LIB_VER_LIBRARY' is set to the version number that is part
of the subdirectory name, if it is in the standard form
(`LIBRARY-VERSION'). If the directory name does not have a
version part, `ERLANG_LIB_VER_LIBRARY' is set to the empty string.
If the library is not installed, `ERLANG_LIB_DIR_LIBRARY' and
`ERLANG_LIB_VER_LIBRARY' are set to `"not found"'. For example,
to check if library `stdlib' is installed:
AC_ERLANG_CHECK_LIB([stdlib],
[echo "stdlib version \"$ERLANG_LIB_VER_stdlib\""
echo "is installed in \"$ERLANG_LIB_DIR_stdlib\""],
[AC_MSG_ERROR([stdlib was not found!])])
In addition to the above macros, which test installed Erlang
libraries, the following macros determine the paths to the directories
into which newly built Erlang libraries are to be installed:
-- Macro: AC_ERLANG_SUBST_INSTALL_LIB_DIR
Set the `ERLANG_INSTALL_LIB_DIR' output variable to the directory
into which every built Erlang library should be installed in a
separate subdirectory. If this variable is not set in the
environment when `configure' runs, its default value is
`$ERLANG_LIB_DIR', which value is set by the
`AC_ERLANG_SUBST_LIB_DIR' macro.
-- Macro: AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR (LIBRARY, VERSION)
Set the `ERLANG_INSTALL_LIB_DIR_LIBRARY' output variable to the
directory into which the built Erlang library LIBRARY version
VERSION should be installed. If this variable is not set in the
environment when `configure' runs, its default value is
`$ERLANG_INSTALL_LIB_DIR/LIBRARY-VERSION', the value of the
`ERLANG_INSTALL_LIB_DIR' variable being set by the
`AC_ERLANG_SUBST_INSTALL_LIB_DIR' macro.

File: autoconf.info, Node: Writing Tests, Next: Results, Prev: Existing Tests, Up: Top
6 Writing Tests
***************
If the existing feature tests don't do something you need, you have to
write new ones. These macros are the building blocks. They provide
ways for other macros to check whether various kinds of features are
available and report the results.
This chapter contains some suggestions and some of the reasons why
the existing tests are written the way they are. You can also learn a
lot about how to write Autoconf tests by looking at the existing ones.
If something goes wrong in one or more of the Autoconf tests, this
information can help you understand the assumptions behind them, which
might help you figure out how to best solve the problem.
These macros check the output of the compiler system of the current
language (*note Language Choice::). They do not cache the results of
their tests for future use (*note Caching Results::), because they don't
know enough about the information they are checking for to generate a
cache variable name. They also do not print any messages, for the same
reason. The checks for particular kinds of features call these macros
and do cache their results and print messages about what they're
checking for.
When you write a feature test that could be applicable to more than
one software package, the best thing to do is encapsulate it in a new
macro. *Note Writing Autoconf Macros::, for how to do that.
* Menu:
* Language Choice:: Selecting which language to use for testing
* Writing Test Programs:: Forging source files for compilers
* Running the Preprocessor:: Detecting preprocessor symbols
* Running the Compiler:: Detecting language or header features
* Running the Linker:: Detecting library features
* Runtime:: Testing for runtime features
* Systemology:: A zoology of operating systems
* Multiple Cases:: Tests for several possible values

File: autoconf.info, Node: Language Choice, Next: Writing Test Programs, Up: Writing Tests
6.1 Language Choice
===================
Autoconf-generated `configure' scripts check for the C compiler and its
features by default. Packages that use other programming languages
(maybe more than one, e.g., C and C++) need to test features of the
compilers for the respective languages. The following macros determine
which programming language is used in the subsequent tests in
`configure.ac'.
-- Macro: AC_LANG (LANGUAGE)
Do compilation tests using the compiler, preprocessor, and file
extensions for the specified LANGUAGE.
Supported languages are:
`C'
Do compilation tests using `CC' and `CPP' and use extension
`.c' for test programs. Use compilation flags: `CPPFLAGS'
with `CPP', and both `CPPFLAGS' and `CFLAGS' with `CC'.
`C++'
Do compilation tests using `CXX' and `CXXCPP' and use
extension `.C' for test programs. Use compilation flags:
`CPPFLAGS' with `CXXPP', and both `CPPFLAGS' and `CXXFLAGS'
with `CXX'.
`Fortran 77'
Do compilation tests using `F77' and use extension `.f' for
test programs. Use compilation flags: `FFLAGS'.
`Fortran'
Do compilation tests using `FC' and use extension `.f' (or
whatever has been set by `AC_FC_SRCEXT') for test programs.
Use compilation flags: `FCFLAGS'.
`Erlang'
Compile and execute tests using `ERLC' and `ERL' and use
extension `.erl' for test Erlang modules. Use compilation
flags: `ERLCFLAGS'.
`Objective C'
Do compilation tests using `OBJC' and `OBJCCPP' and use
extension `.m' for test programs. Use compilation flags:
`CPPFLAGS' with `OBJCPP', and both `CPPFLAGS' and `OBJCFLAGS'
with `OBJC'.
-- Macro: AC_LANG_PUSH (LANGUAGE)
Remember the current language (as set by `AC_LANG') on a stack, and
then select the LANGUAGE. Use this macro and `AC_LANG_POP' in
macros that need to temporarily switch to a particular language.
-- Macro: AC_LANG_POP ([LANGUAGE])
Select the language that is saved on the top of the stack, as set
by `AC_LANG_PUSH', and remove it from the stack.
If given, LANGUAGE specifies the language we just _quit_. It is a
good idea to specify it when it's known (which should be the
case...), since Autoconf detects inconsistencies.
AC_LANG_PUSH([Fortran 77])
# Perform some tests on Fortran 77.
# ...
AC_LANG_POP([Fortran 77])
-- Macro: AC_LANG_ASSERT (LANGUAGE)
Check statically that the current language is LANGUAGE. You
should use this in your language specific macros to avoid that
they be called with an inappropriate language.
This macro runs only at `autoconf' time, and incurs no cost at
`configure' time. Sadly enough and because Autoconf is a two
layer language (1), the macros `AC_LANG_PUSH' and `AC_LANG_POP'
cannot be "optimizing", therefore as much as possible you ought to
avoid using them to wrap your code, rather, require from the user
to run the macro with a correct current language, and check it
with `AC_LANG_ASSERT'. And anyway, that may help the user
understand she is running a Fortran macro while expecting a result
about her Fortran 77 compiler...
-- Macro: AC_REQUIRE_CPP
Ensure that whichever preprocessor would currently be used for
tests has been found. Calls `AC_REQUIRE' (*note Prerequisite
Macros::) with an argument of either `AC_PROG_CPP' or
`AC_PROG_CXXCPP', depending on which language is current.
---------- Footnotes ----------
(1) Because M4 is not aware of Sh code, especially conditionals,
some optimizations that look nice statically may produce incorrect
results at runtime.

File: autoconf.info, Node: Writing Test Programs, Next: Running the Preprocessor, Prev: Language Choice, Up: Writing Tests
6.2 Writing Test Programs
=========================
Autoconf tests follow a common scheme: feed some program with some
input, and most of the time, feed a compiler with some source file.
This section is dedicated to these source samples.
* Menu:
* Guidelines:: General rules for writing test programs
* Test Functions:: Avoiding pitfalls in test programs
* Generating Sources:: Source program boilerplate

File: autoconf.info, Node: Guidelines, Next: Test Functions, Up: Writing Test Programs
6.2.1 Guidelines for Test Programs
----------------------------------
The most important rule to follow when writing testing samples is:
_Look for realism._
This motto means that testing samples must be written with the same
strictness as real programs are written. In particular, you should
avoid "shortcuts" and simplifications.
Don't just play with the preprocessor if you want to prepare a
compilation. For instance, using `cpp' to check whether a header is
functional might let your `configure' accept a header which causes some
_compiler_ error. Do not hesitate to check a header with other headers
included before, especially required headers.
Make sure the symbols you use are properly defined, i.e., refrain for
simply declaring a function yourself instead of including the proper
header.
Test programs should not write to standard output. They should exit
with status 0 if the test succeeds, and with status 1 otherwise, so
that success can be distinguished easily from a core dump or other
failure; segmentation violations and other failures produce a nonzero
exit status. Unless you arrange for `exit' to be declared, test
programs should `return', not `exit', from `main', because on many
systems `exit' is not declared by default.
Test programs can use `#if' or `#ifdef' to check the values of
preprocessor macros defined by tests that have already run. For
example, if you call `AC_HEADER_STDBOOL', then later on in
`configure.ac' you can have a test program that includes `stdbool.h'
conditionally:
#ifdef HAVE_STDBOOL_H
# include <stdbool.h>
#endif
Both `#if HAVE_STDBOOL_H' and `#ifdef HAVE_STDBOOL_H' will work with
any standard C compiler. Some developers prefer `#if' because it is
easier to read, while others prefer `#ifdef' because it avoids
diagnostics with picky compilers like GCC with the `-Wundef' option.
If a test program needs to use or create a data file, give it a name
that starts with `conftest', such as `conftest.data'. The `configure'
script cleans up by running `rm -f -r conftest*' after running test
programs and if the script is interrupted.

File: autoconf.info, Node: Test Functions, Next: Generating Sources, Prev: Guidelines, Up: Writing Test Programs
6.2.2 Test Functions
--------------------
These days it's safe to assume support for function prototypes
(introduced in C89).
Functions that test programs declare should also be conditionalized
for C++, which requires `extern "C"' prototypes. Make sure to not
include any header files containing clashing prototypes.
#ifdef __cplusplus
extern "C"
#endif
void *valloc (size_t);
If a test program calls a function with invalid parameters (just to
see whether it exists), organize the program to ensure that it never
invokes that function. You can do this by calling it in another
function that is never invoked. You can't do it by putting it after a
call to `exit', because GCC version 2 knows that `exit' never returns
and optimizes out any code that follows it in the same block.
If you include any header files, be sure to call the functions
relevant to them with the correct number of arguments, even if they are
just 0, to avoid compilation errors due to prototypes. GCC version 2
has internal prototypes for several functions that it automatically
inlines; for example, `memcpy'. To avoid errors when checking for
them, either pass them the correct number of arguments or redeclare them
with a different return type (such as `char').

File: autoconf.info, Node: Generating Sources, Prev: Test Functions, Up: Writing Test Programs
6.2.3 Generating Sources
------------------------
Autoconf provides a set of macros that can be used to generate test
source files. They are written to be language generic, i.e., they
actually depend on the current language (*note Language Choice::) to
"format" the output properly.
-- Macro: AC_LANG_CONFTEST (SOURCE)
Save the SOURCE text in the current test source file:
`conftest.EXTENSION' where the EXTENSION depends on the current
language.
Note that the SOURCE is evaluated exactly once, like regular
Autoconf macro arguments, and therefore (i) you may pass a macro
invocation, (ii) if not, be sure to double quote if needed.
-- Macro: AC_LANG_SOURCE (SOURCE)
Expands into the SOURCE, with the definition of all the
`AC_DEFINE' performed so far.
For instance executing (observe the double quotation!):
AC_INIT([Hello], [1.0], [bug-hello@example.org])
AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
[Greetings string.])
AC_LANG(C)
AC_LANG_CONFTEST(
[AC_LANG_SOURCE([[const char hw[] = "Hello, World\n";]])])
gcc -E -dD -o - conftest.c
results in:
...
# 1 "conftest.c"
#define PACKAGE_NAME "Hello"
#define PACKAGE_TARNAME "hello"
#define PACKAGE_VERSION "1.0"
#define PACKAGE_STRING "Hello 1.0"
#define PACKAGE_BUGREPORT "bug-hello@example.org"
#define HELLO_WORLD "Hello, World\n"
const char hw[] = "Hello, World\n";
When the test language is Fortran or Erlang, the `AC_DEFINE'
definitions are not automatically translated into constants in the
source code by this macro.
-- Macro: AC_LANG_PROGRAM (PROLOGUE, BODY)
Expands into a source file which consists of the PROLOGUE, and
then BODY as body of the main function (e.g., `main' in C). Since
it uses `AC_LANG_SOURCE', the features of the latter are available.
For instance:
AC_INIT([Hello], [1.0], [bug-hello@example.org])
AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
[Greetings string.])
AC_LANG_CONFTEST(
[AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]],
[[fputs (hw, stdout);]])])
gcc -E -dD -o - conftest.c
results in:
...
# 1 "conftest.c"
#define PACKAGE_NAME "Hello"
#define PACKAGE_TARNAME "hello"
#define PACKAGE_VERSION "1.0"
#define PACKAGE_STRING "Hello 1.0"
#define PACKAGE_BUGREPORT "bug-hello@example.org"
#define HELLO_WORLD "Hello, World\n"
const char hw[] = "Hello, World\n";
int
main ()
{
fputs (hw, stdout);
;
return 0;
}
In Erlang tests, the created source file is that of an Erlang module
called `conftest' (`conftest.erl'). This module defines and exports at
least one `start/0' function, which is called to perform the test. The
PROLOGUE is optional code that is inserted between the module header and
the `start/0' function definition. BODY is the body of the `start/0'
function without the final period (*note Runtime::, about constraints
on this function's behavior).
For instance:
AC_INIT([Hello], [1.0], [bug-hello@example.org])
AC_LANG(Erlang)
AC_LANG_CONFTEST(
[AC_LANG_PROGRAM([[-define(HELLO_WORLD, "Hello, world!").]],
[[io:format("~s~n", [?HELLO_WORLD])]])])
cat conftest.erl
results in:
-module(conftest).
-export([start/0]).
-define(HELLO_WORLD, "Hello, world!").
start() ->
io:format("~s~n", [?HELLO_WORLD])
.
-- Macro: AC_LANG_CALL (PROLOGUE, FUNCTION)
Expands into a source file which consists of the PROLOGUE, and
then a call to the FUNCTION as body of the main function (e.g.,
`main' in C). Since it uses `AC_LANG_PROGRAM', the feature of the
latter are available.
This function will probably be replaced in the future by a version
which would enable specifying the arguments. The use of this
macro is not encouraged, as it violates strongly the typing system.
This macro cannot be used for Erlang tests.
-- Macro: AC_LANG_FUNC_LINK_TRY (FUNCTION)
Expands into a source file which uses the FUNCTION in the body of
the main function (e.g., `main' in C). Since it uses
`AC_LANG_PROGRAM', the features of the latter are available.
As `AC_LANG_CALL', this macro is documented only for completeness.
It is considered to be severely broken, and in the future will be
removed in favor of actual function calls (with properly typed
arguments).
This macro cannot be used for Erlang tests.

File: autoconf.info, Node: Running the Preprocessor, Next: Running the Compiler, Prev: Writing Test Programs, Up: Writing Tests
6.3 Running the Preprocessor
============================
Sometimes one might need to run the preprocessor on some source file.
_Usually it is a bad idea_, as you typically need to _compile_ your
project, not merely run the preprocessor on it; therefore you certainly
want to run the compiler, not the preprocessor. Resist the temptation
of following the easiest path.
Nevertheless, if you need to run the preprocessor, then use
`AC_PREPROC_IFELSE'.
The macros described in this section cannot be used for tests in
Erlang or Fortran, since those languages require no preprocessor.
-- Macro: AC_PREPROC_IFELSE (INPUT, [ACTION-IF-TRUE],
[ACTION-IF-FALSE])
Run the preprocessor of the current language (*note Language
Choice::) on the INPUT, run the shell commands ACTION-IF-TRUE on
success, ACTION-IF-FALSE otherwise. The INPUT can be made by
`AC_LANG_PROGRAM' and friends.
This macro uses `CPPFLAGS', but not `CFLAGS', because `-g', `-O',
etc. are not valid options to many C preprocessors.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'.
For instance:
AC_INIT([Hello], [1.0], [bug-hello@example.org])
AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
[Greetings string.])
AC_PREPROC_IFELSE(
[AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]],
[[fputs (hw, stdout);]])],
[AC_MSG_RESULT([OK])],
[AC_MSG_FAILURE([unexpected preprocessor failure])])
results in:
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -E
OK
The macro `AC_TRY_CPP' (*note Obsolete Macros::) used to play the
role of `AC_PREPROC_IFELSE', but double quotes its argument, making it
impossible to use it to elaborate sources. You are encouraged to get
rid of your old use of the macro `AC_TRY_CPP' in favor of
`AC_PREPROC_IFELSE', but, in the first place, are you sure you need to
run the _preprocessor_ and not the compiler?
-- Macro: AC_EGREP_HEADER (PATTERN, HEADER-FILE, ACTION-IF-FOUND,
[ACTION-IF-NOT-FOUND])
If the output of running the preprocessor on the system header file
HEADER-FILE matches the extended regular expression PATTERN,
execute shell commands ACTION-IF-FOUND, otherwise execute
ACTION-IF-NOT-FOUND.
-- Macro: AC_EGREP_CPP (PATTERN, PROGRAM, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
PROGRAM is the text of a C or C++ program, on which shell
variable, back quote, and backslash substitutions are performed.
If the output of running the preprocessor on PROGRAM matches the
extended regular expression PATTERN, execute shell commands
ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.

File: autoconf.info, Node: Running the Compiler, Next: Running the Linker, Prev: Running the Preprocessor, Up: Writing Tests
6.4 Running the Compiler
========================
To check for a syntax feature of the current language's (*note Language
Choice::) compiler, such as whether it recognizes a certain keyword, or
simply to try some library feature, use `AC_COMPILE_IFELSE' to try to
compile a small program that uses that feature.
-- Macro: AC_COMPILE_IFELSE (INPUT, [ACTION-IF-TRUE],
[ACTION-IF-FALSE])
Run the compiler and compilation flags of the current language
(*note Language Choice::) on the INPUT, run the shell commands
ACTION-IF-TRUE on success, ACTION-IF-FALSE otherwise. The INPUT
can be made by `AC_LANG_PROGRAM' and friends.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'. This macro does not try to link; use
`AC_LINK_IFELSE' if you need to do that (*note Running the
Linker::).
For tests in Erlang, the INPUT must be the source code of a module
named `conftest'. `AC_COMPILE_IFELSE' generates a `conftest.beam' file
that can be interpreted by the Erlang virtual machine (`ERL'). It is
recommended to use `AC_LANG_PROGRAM' to specify the test program, to
ensure that the Erlang module has the right name.

File: autoconf.info, Node: Running the Linker, Next: Runtime, Prev: Running the Compiler, Up: Writing Tests
6.5 Running the Linker
======================
To check for a library, a function, or a global variable, Autoconf
`configure' scripts try to compile and link a small program that uses
it. This is unlike Metaconfig, which by default uses `nm' or `ar' on
the C library to try to figure out which functions are available.
Trying to link with the function is usually a more reliable approach
because it avoids dealing with the variations in the options and output
formats of `nm' and `ar' and in the location of the standard libraries.
It also allows configuring for cross-compilation or checking a
function's runtime behavior if needed. On the other hand, it can be
slower than scanning the libraries once, but accuracy is more important
than speed.
`AC_LINK_IFELSE' is used to compile test programs to test for
functions and global variables. It is also used by `AC_CHECK_LIB' to
check for libraries (*note Libraries::), by adding the library being
checked for to `LIBS' temporarily and trying to link a small program.
-- Macro: AC_LINK_IFELSE (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
Run the compiler (and compilation flags) and the linker of the
current language (*note Language Choice::) on the INPUT, run the
shell commands ACTION-IF-TRUE on success, ACTION-IF-FALSE
otherwise. The INPUT can be made by `AC_LANG_PROGRAM' and friends.
`LDFLAGS' and `LIBS' are used for linking, in addition to the
current compilation flags.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'. This macro does not try to execute the program;
use `AC_RUN_IFELSE' if you need to do that (*note Runtime::).
The `AC_LINK_IFELSE' macro cannot be used for Erlang tests, since
Erlang programs are interpreted and do not require linking.

File: autoconf.info, Node: Runtime, Next: Systemology, Prev: Running the Linker, Up: Writing Tests
6.6 Checking Runtime Behavior
=============================
Sometimes you need to find out how a system performs at runtime, such
as whether a given function has a certain capability or bug. If you
can, make such checks when your program runs instead of when it is
configured. You can check for things like the machine's endianness when
your program initializes itself.
If you really need to test for a runtime behavior while configuring,
you can write a test program to determine the result, and compile and
run it using `AC_RUN_IFELSE'. Avoid running test programs if possible,
because this prevents people from configuring your package for
cross-compiling.
-- Macro: AC_RUN_IFELSE (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE],
[ACTION-IF-CROSS-COMPILING])
If PROGRAM compiles and links successfully and returns an exit
status of 0 when executed, run shell commands ACTION-IF-TRUE.
Otherwise, run shell commands ACTION-IF-FALSE.
The INPUT can be made by `AC_LANG_PROGRAM' and friends. `LDFLAGS'
and `LIBS' are used for linking, in addition to the compilation
flags of the current language (*note Language Choice::).
If the compiler being used does not produce executables that run
on the system where `configure' is being run, then the test
program is not run. If the optional shell commands
ACTION-IF-CROSS-COMPILING are given, they are run instead.
Otherwise, `configure' prints an error message and exits.
In the ACTION-IF-FALSE section, the failing exit status is
available in the shell variable `$?'. This exit status might be
that of a failed compilation, or it might be that of a failed
program execution.
It is customary to report unexpected failures with
`AC_MSG_FAILURE'.
Try to provide a pessimistic default value to use when
cross-compiling makes runtime tests impossible. You do this by passing
the optional last argument to `AC_RUN_IFELSE'. `autoconf' prints a
warning message when creating `configure' each time it encounters a
call to `AC_RUN_IFELSE' with no ACTION-IF-CROSS-COMPILING argument
given. You may ignore the warning, though users cannot configure your
package for cross-compiling. A few of the macros distributed with
Autoconf produce this warning message.
To configure for cross-compiling you can also choose a value for
those parameters based on the canonical system name (*note Manual
Configuration::). Alternatively, set up a test results cache file with
the correct values for the host system (*note Caching Results::).
To provide a default for calls of `AC_RUN_IFELSE' that are embedded
in other macros, including a few of the ones that come with Autoconf,
you can test whether the shell variable `cross_compiling' is set to
`yes', and then use an alternate method to get the results instead of
calling the macros.
A C or C++ runtime test should be portable. *Note Portable C and
C++::.
Erlang tests must exit themselves the Erlang VM by calling the
`halt/1' function: the given status code is used to determine the
success of the test (status is `0') or its failure (status is different
than `0'), as explained above. It must be noted that data output
through the standard output (e.g., using `io:format/2') may be
truncated when halting the VM. Therefore, if a test must output
configuration information, it is recommended to create and to output
data into the temporary file named `conftest.out', using the functions
of module `file'. The `conftest.out' file is automatically deleted by
the `AC_RUN_IFELSE' macro. For instance, a simplified implementation
of Autoconf's `AC_ERLANG_SUBST_LIB_DIR' macro is:
AC_INIT([LibdirTest], [1.0], [bug-libdirtest@example.org])
AC_ERLANG_NEED_ERL
AC_LANG(Erlang)
AC_RUN_IFELSE(
[AC_LANG_PROGRAM([], [dnl
file:write_file("conftest.out", code:lib_dir()),
halt(0)])],
[echo "code:lib_dir() returned: `cat conftest.out`"],
[AC_MSG_FAILURE([test Erlang program execution failed])])

File: autoconf.info, Node: Systemology, Next: Multiple Cases, Prev: Runtime, Up: Writing Tests
6.7 Systemology
===============
This section aims at presenting some systems and pointers to
documentation. It may help you addressing particular problems reported
by users.
Posix-conforming systems (http://www.opengroup.org/susv3) are
derived from the Unix operating system
(http://www.bell-labs.com/history/unix/).
The Rosetta Stone for Unix (http://bhami.com/rosetta.html) contains
a table correlating the features of various Posix-conforming systems.
Unix History (http://www.levenez.com/unix/) is a simplified diagram of
how many Unix systems were derived from each other.
The Heirloom Project (http://heirloom.sourceforge.net/) provides
some variants of traditional implementations of Unix utilities.
Darwin
Darwin is also known as Mac OS X. Beware that the file system
_can_ be case-preserving, but case insensitive. This can cause
nasty problems, since for instance the installation attempt for a
package having an `INSTALL' file can result in `make install'
report that nothing was to be done!
That's all dependent on whether the file system is a UFS (case
sensitive) or HFS+ (case preserving). By default Apple wants you
to install the OS on HFS+. Unfortunately, there are some pieces of
software which really need to be built on UFS. We may want to
rebuild Darwin to have both UFS and HFS+ available (and put the
/local/build tree on the UFS).
QNX 4.25
QNX is a realtime operating system running on Intel architecture
meant to be scalable from the small embedded systems to the hundred
processor super-computer. It claims to be Posix certified. More
information is available on the QNX home page
(http://www.qnx.com/).
Tru64
Documentation of several versions of Tru64
(http://h30097.www3.hp.com/docs/) is available in different
formats.
Unix version 7
Officially this was called the "Seventh Edition" of "the UNIX
time-sharing system" but we use the more-common name "Unix version
7". Documentation is available in the Unix Seventh Edition Manual
(http://plan9.bell-labs.com/7thEdMan/). Previous versions of Unix
are called "Unix version 6", etc., but they were not as widely
used.

File: autoconf.info, Node: Multiple Cases, Prev: Systemology, Up: Writing Tests
6.8 Multiple Cases
==================
Some operations are accomplished in several possible ways, depending on
the OS variant. Checking for them essentially requires a "case
statement". Autoconf does not directly provide one; however, it is
easy to simulate by using a shell variable to keep track of whether a
way to perform the operation has been found yet.
Here is an example that uses the shell variable `fstype' to keep
track of whether the remaining cases need to be checked.
AC_MSG_CHECKING([how to get file system type])
fstype=no
# The order of these tests is important.
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statvfs.h>
#include <sys/fstyp.h>]])],
[AC_DEFINE([FSTYPE_STATVFS], [1],
[Define if statvfs exists.])
fstype=SVR4])
if test $fstype = no; then
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h>
#include <sys/fstyp.h>]])],
[AC_DEFINE([FSTYPE_USG_STATFS], [1],
[Define if USG statfs.])
fstype=SVR3])
fi
if test $fstype = no; then
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h>
#include <sys/vmount.h>]])]),
[AC_DEFINE([FSTYPE_AIX_STATFS], [1],
[Define if AIX statfs.])
fstype=AIX])
fi
# (more cases omitted here)
AC_MSG_RESULT([$fstype])

File: autoconf.info, Node: Results, Next: Programming in M4, Prev: Writing Tests, Up: Top
7 Results of Tests
******************
Once `configure' has determined whether a feature exists, what can it
do to record that information? There are four sorts of things it can
do: define a C preprocessor symbol, set a variable in the output files,
save the result in a cache file for future `configure' runs, and print
a message letting the user know the result of the test.
* Menu:
* Defining Symbols:: Defining C preprocessor symbols
* Setting Output Variables:: Replacing variables in output files
* Special Chars in Variables:: Characters to beware of in variables
* Caching Results:: Speeding up subsequent `configure' runs
* Printing Messages:: Notifying `configure' users

File: autoconf.info, Node: Defining Symbols, Next: Setting Output Variables, Up: Results
7.1 Defining C Preprocessor Symbols
===================================
A common action to take in response to a feature test is to define a C
preprocessor symbol indicating the results of the test. That is done by
calling `AC_DEFINE' or `AC_DEFINE_UNQUOTED'.
By default, `AC_OUTPUT' places the symbols defined by these macros
into the output variable `DEFS', which contains an option
`-DSYMBOL=VALUE' for each symbol defined. Unlike in Autoconf version
1, there is no variable `DEFS' defined while `configure' is running.
To check whether Autoconf macros have already defined a certain C
preprocessor symbol, test the value of the appropriate cache variable,
as in this example:
AC_CHECK_FUNC([vprintf], [AC_DEFINE([HAVE_VPRINTF], [1],
[Define if vprintf exists.])])
if test "$ac_cv_func_vprintf" != yes; then
AC_CHECK_FUNC([_doprnt], [AC_DEFINE([HAVE_DOPRNT], [1],
[Define if _doprnt exists.])])
fi
If `AC_CONFIG_HEADERS' has been called, then instead of creating
`DEFS', `AC_OUTPUT' creates a header file by substituting the correct
values into `#define' statements in a template file. *Note
Configuration Headers::, for more information about this kind of output.
-- Macro: AC_DEFINE (VARIABLE, VALUE, [DESCRIPTION])
-- Macro: AC_DEFINE (VARIABLE)
Define the C preprocessor variable VARIABLE to VALUE (verbatim).
VALUE should not contain literal newlines, and if you are not
using `AC_CONFIG_HEADERS' it should not contain any `#'
characters, as `make' tends to eat them. To use a shell variable,
use `AC_DEFINE_UNQUOTED' instead. DESCRIPTION is only useful if
you are using `AC_CONFIG_HEADERS'. In this case, DESCRIPTION is
put into the generated `config.h.in' as the comment before the
macro define. The following example defines the C preprocessor
variable `EQUATION' to be the string constant `"$a > $b"':
AC_DEFINE([EQUATION], ["$a > $b"],
[Equation string.])
If neither VALUE nor DESCRIPTION are given, then VALUE defaults to
1 instead of to the empty string. This is for backwards
compatibility with older versions of Autoconf, but this usage is
obsolescent and may be withdrawn in future versions of Autoconf.
If the VARIABLE is a literal string, it is passed to
`m4_pattern_allow' (*note Forbidden Patterns::).
-- Macro: AC_DEFINE_UNQUOTED (VARIABLE, VALUE, [DESCRIPTION])
-- Macro: AC_DEFINE_UNQUOTED (VARIABLE)
Like `AC_DEFINE', but three shell expansions are
performed--once--on VARIABLE and VALUE: variable expansion (`$'),
command substitution (``'), and backslash escaping (`\'). Single
and double quote characters in the value have no special meaning.
Use this macro instead of `AC_DEFINE' when VARIABLE or VALUE is a
shell variable. Examples:
AC_DEFINE_UNQUOTED([config_machfile], ["$machfile"],
[Configuration machine file.])
AC_DEFINE_UNQUOTED([GETGROUPS_T], [$ac_cv_type_getgroups],
[getgroups return type.])
AC_DEFINE_UNQUOTED([$ac_tr_hdr], [1],
[Translated header name.])
Due to a syntactical bizarreness of the Bourne shell, do not use
semicolons to separate `AC_DEFINE' or `AC_DEFINE_UNQUOTED' calls from
other macro calls or shell code; that can cause syntax errors in the
resulting `configure' script. Use either blanks or newlines. That is,
do this:
AC_CHECK_HEADER([elf.h],
[AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"])
or this:
AC_CHECK_HEADER([elf.h],
[AC_DEFINE([SVR4], [1], [System V Release 4])
LIBS="-lelf $LIBS"])
instead of this:
AC_CHECK_HEADER([elf.h],
[AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="-lelf $LIBS"])

File: autoconf.info, Node: Setting Output Variables, Next: Special Chars in Variables, Prev: Defining Symbols, Up: Results
7.2 Setting Output Variables
============================
Another way to record the results of tests is to set "output
variables", which are shell variables whose values are substituted into
files that `configure' outputs. The two macros below create new output
variables. *Note Preset Output Variables::, for a list of output
variables that are always available.
-- Macro: AC_SUBST (VARIABLE, [VALUE])
Create an output variable from a shell variable. Make `AC_OUTPUT'
substitute the variable VARIABLE into output files (typically one
or more makefiles). This means that `AC_OUTPUT' replaces
instances of `@VARIABLE@' in input files with the value that the
shell variable VARIABLE has when `AC_OUTPUT' is called. The value
can contain newlines. The substituted value is not rescanned for
more output variables; occurrences of `@VARIABLE@' in the value
are inserted literally into the output file. (The algorithm uses
the special marker `|#_!!_#|' internally, so the substituted value
cannot contain `|#_!!_#|'.)
If VALUE is given, in addition assign it to VARIABLE.
The string VARIABLE is passed to `m4_pattern_allow' (*note
Forbidden Patterns::).
-- Macro: AC_SUBST_FILE (VARIABLE)
Another way to create an output variable from a shell variable.
Make `AC_OUTPUT' insert (without substitutions) the contents of
the file named by shell variable VARIABLE into output files. This
means that `AC_OUTPUT' replaces instances of `@VARIABLE@' in
output files (such as `Makefile.in') with the contents of the file
that the shell variable VARIABLE names when `AC_OUTPUT' is called.
Set the variable to `/dev/null' for cases that do not have a file
to insert. This substitution occurs only when the `@VARIABLE@' is
on a line by itself, optionally surrounded by spaces and tabs. The
substitution replaces the whole line, including the spaces, tabs,
and the terminating newline.
This macro is useful for inserting makefile fragments containing
special dependencies or other `make' directives for particular host
or target types into makefiles. For example, `configure.ac' could
contain:
AC_SUBST_FILE([host_frag])
host_frag=$srcdir/conf/sun4.mh
and then a `Makefile.in' could contain:
@host_frag@
The string VARIABLE is passed to `m4_pattern_allow' (*note
Forbidden Patterns::).
Running `configure' in varying environments can be extremely
dangerous. If for instance the user runs `CC=bizarre-cc ./configure',
then the cache, `config.h', and many other output files depend upon
`bizarre-cc' being the C compiler. If for some reason the user runs
`./configure' again, or if it is run via `./config.status --recheck',
(*Note Automatic Remaking::, and *note config.status Invocation::),
then the configuration can be inconsistent, composed of results
depending upon two different compilers.
Environment variables that affect this situation, such as `CC'
above, are called "precious variables", and can be declared as such by
`AC_ARG_VAR'.
-- Macro: AC_ARG_VAR (VARIABLE, DESCRIPTION)
Declare VARIABLE is a precious variable, and include its
DESCRIPTION in the variable section of `./configure --help'.
Being precious means that
- VARIABLE is substituted via `AC_SUBST'.
- The value of VARIABLE when `configure' was launched is saved
in the cache, including if it was not specified on the command
line but via the environment. Indeed, while `configure' can
notice the definition of `CC' in `./configure CC=bizarre-cc',
it is impossible to notice it in `CC=bizarre-cc ./configure',
which, unfortunately, is what most users do.
We emphasize that it is the _initial_ value of VARIABLE which
is saved, not that found during the execution of `configure'.
Indeed, specifying `./configure FOO=foo' and letting
`./configure' guess that `FOO' is `foo' can be two different
things.
- VARIABLE is checked for consistency between two `configure'
runs. For instance:
$ ./configure --silent --config-cache
$ CC=cc ./configure --silent --config-cache
configure: error: `CC' was not set in the previous run
configure: error: changes in the environment can compromise \
the build
configure: error: run `make distclean' and/or \
`rm config.cache' and start over
and similarly if the variable is unset, or if its content is
changed.
- VARIABLE is kept during automatic reconfiguration (*note
config.status Invocation::) as if it had been passed as a
command line argument, including when no cache is used:
$ CC=/usr/bin/cc ./configure undeclared_var=raboof --silent
$ ./config.status --recheck
running CONFIG_SHELL=/bin/sh /bin/sh ./configure undeclared_var=raboof \
CC=/usr/bin/cc --no-create --no-recursion

File: autoconf.info, Node: Special Chars in Variables, Next: Caching Results, Prev: Setting Output Variables, Up: Results
7.3 Special Characters in Output Variables
==========================================
Many output variables are intended to be evaluated both by `make' and
by the shell. Some characters are expanded differently in these two
contexts, so to avoid confusion these variables' values should not
contain any of the following characters:
" # $ & ' ( ) * ; < > ? [ \ ^ ` |
Also, these variables' values should neither contain newlines, nor
start with `~', nor contain white space or `:' immediately followed by
`~'. The values can contain nonempty sequences of white space
characters like tabs and spaces, but each such sequence might
arbitrarily be replaced by a single space during substitution.
These restrictions apply both to the values that `configure'
computes, and to the values set directly by the user. For example, the
following invocations of `configure' are problematic, since they
attempt to use special characters within `CPPFLAGS' and white space
within `$(srcdir)':
CPPFLAGS='-DOUCH="&\"#$*?"' '../My Source/ouch-1.0/configure'
'../My Source/ouch-1.0/configure' CPPFLAGS='-DOUCH="&\"#$*?"'

File: autoconf.info, Node: Caching Results, Next: Printing Messages, Prev: Special Chars in Variables, Up: Results
7.4 Caching Results
===================
To avoid checking for the same features repeatedly in various
`configure' scripts (or in repeated runs of one script), `configure'
can optionally save the results of many checks in a "cache file" (*note
Cache Files::). If a `configure' script runs with caching enabled and
finds a cache file, it reads the results of previous runs from the
cache and avoids rerunning those checks. As a result, `configure' can
then run much faster than if it had to perform all of the checks every
time.
-- Macro: AC_CACHE_VAL (CACHE-ID, COMMANDS-TO-SET-IT)
Ensure that the results of the check identified by CACHE-ID are
available. If the results of the check were in the cache file
that was read, and `configure' was not given the `--quiet' or
`--silent' option, print a message saying that the result was
cached; otherwise, run the shell commands COMMANDS-TO-SET-IT. If
the shell commands are run to determine the value, the value is
saved in the cache file just before `configure' creates its output
files. *Note Cache Variable Names::, for how to choose the name
of the CACHE-ID variable.
The COMMANDS-TO-SET-IT _must have no side effects_ except for
setting the variable CACHE-ID, see below.
-- Macro: AC_CACHE_CHECK (MESSAGE, CACHE-ID, COMMANDS-TO-SET-IT)
A wrapper for `AC_CACHE_VAL' that takes care of printing the
messages. This macro provides a convenient shorthand for the most
common way to use these macros. It calls `AC_MSG_CHECKING' for
MESSAGE, then `AC_CACHE_VAL' with the CACHE-ID and COMMANDS
arguments, and `AC_MSG_RESULT' with CACHE-ID.
The COMMANDS-TO-SET-IT _must have no side effects_ except for
setting the variable CACHE-ID, see below.
It is common to find buggy macros using `AC_CACHE_VAL' or
`AC_CACHE_CHECK', because people are tempted to call `AC_DEFINE' in the
COMMANDS-TO-SET-IT. Instead, the code that _follows_ the call to
`AC_CACHE_VAL' should call `AC_DEFINE', by examining the value of the
cache variable. For instance, the following macro is broken:
AC_DEFUN([AC_SHELL_TRUE],
[AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works],
[ac_cv_shell_true_works=no
(true) 2>/dev/null && ac_cv_shell_true_works=yes
if test "$ac_cv_shell_true_works" = yes; then
AC_DEFINE([TRUE_WORKS], [1],
[Define if `true(1)' works properly.])
fi])
])
This fails if the cache is enabled: the second time this macro is run,
`TRUE_WORKS' _will not be defined_. The proper implementation is:
AC_DEFUN([AC_SHELL_TRUE],
[AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works],
[ac_cv_shell_true_works=no
(true) 2>/dev/null && ac_cv_shell_true_works=yes])
if test "$ac_cv_shell_true_works" = yes; then
AC_DEFINE([TRUE_WORKS], [1],
[Define if `true(1)' works properly.])
fi
])
Also, COMMANDS-TO-SET-IT should not print any messages, for example
with `AC_MSG_CHECKING'; do that before calling `AC_CACHE_VAL', so the
messages are printed regardless of whether the results of the check are
retrieved from the cache or determined by running the shell commands.
* Menu:
* Cache Variable Names:: Shell variables used in caches
* Cache Files:: Files `configure' uses for caching
* Cache Checkpointing:: Loading and saving the cache file

File: autoconf.info, Node: Cache Variable Names, Next: Cache Files, Up: Caching Results
7.4.1 Cache Variable Names
--------------------------
The names of cache variables should have the following format:
PACKAGE-PREFIX_cv_VALUE-TYPE_SPECIFIC-VALUE_[ADDITIONAL-OPTIONS]
for example, `ac_cv_header_stat_broken' or
`ac_cv_prog_gcc_traditional'. The parts of the variable name are:
PACKAGE-PREFIX
An abbreviation for your package or organization; the same prefix
you begin local Autoconf macros with, except lowercase by
convention. For cache values used by the distributed Autoconf
macros, this value is `ac'.
`_cv_'
Indicates that this shell variable is a cache value. This string
_must_ be present in the variable name, including the leading
underscore.
VALUE-TYPE
A convention for classifying cache values, to produce a rational
naming system. The values used in Autoconf are listed in *Note
Macro Names::.
SPECIFIC-VALUE
Which member of the class of cache values this test applies to.
For example, which function (`alloca'), program (`gcc'), or output
variable (`INSTALL').
ADDITIONAL-OPTIONS
Any particular behavior of the specific member that this test
applies to. For example, `broken' or `set'. This part of the
name may be omitted if it does not apply.
The values assigned to cache variables may not contain newlines.
Usually, their values are Boolean (`yes' or `no') or the names of files
or functions; so this is not an important restriction.

File: autoconf.info, Node: Cache Files, Next: Cache Checkpointing, Prev: Cache Variable Names, Up: Caching Results
7.4.2 Cache Files
-----------------
A cache file is a shell script that caches the results of configure
tests run on one system so they can be shared between configure scripts
and configure runs. It is not useful on other systems. If its contents
are invalid for some reason, the user may delete or edit it.
By default, `configure' uses no cache file, to avoid problems caused
by accidental use of stale cache files.
To enable caching, `configure' accepts `--config-cache' (or `-C') to
cache results in the file `config.cache'. Alternatively,
`--cache-file=FILE' specifies that FILE be the cache file. The cache
file is created if it does not exist already. When `configure' calls
`configure' scripts in subdirectories, it uses the `--cache-file'
argument so that they share the same cache. *Note Subdirectories::,
for information on configuring subdirectories with the
`AC_CONFIG_SUBDIRS' macro.
`config.status' only pays attention to the cache file if it is given
the `--recheck' option, which makes it rerun `configure'.
It is wrong to try to distribute cache files for particular system
types. There is too much room for error in doing that, and too much
administrative overhead in maintaining them. For any features that
can't be guessed automatically, use the standard method of the canonical
system type and linking files (*note Manual Configuration::).
The site initialization script can specify a site-wide cache file to
use, instead of the usual per-program cache. In this case, the cache
file gradually accumulates information whenever someone runs a new
`configure' script. (Running `configure' merges the new cache results
with the existing cache file.) This may cause problems, however, if
the system configuration (e.g., the installed libraries or compilers)
changes and the stale cache file is not deleted.

File: autoconf.info, Node: Cache Checkpointing, Prev: Cache Files, Up: Caching Results
7.4.3 Cache Checkpointing
-------------------------
If your configure script, or a macro called from `configure.ac', happens
to abort the configure process, it may be useful to checkpoint the cache
a few times at key points using `AC_CACHE_SAVE'. Doing so reduces the
amount of time it takes to rerun the configure script with (hopefully)
the error that caused the previous abort corrected.
-- Macro: AC_CACHE_LOAD
Loads values from existing cache file, or creates a new cache file
if a cache file is not found. Called automatically from `AC_INIT'.
-- Macro: AC_CACHE_SAVE
Flushes all cached values to the cache file. Called automatically
from `AC_OUTPUT', but it can be quite useful to call
`AC_CACHE_SAVE' at key points in `configure.ac'.
For instance:
... AC_INIT, etc. ...
# Checks for programs.
AC_PROG_CC
AC_PROG_AWK
... more program checks ...
AC_CACHE_SAVE
# Checks for libraries.
AC_CHECK_LIB([nsl], [gethostbyname])
AC_CHECK_LIB([socket], [connect])
... more lib checks ...
AC_CACHE_SAVE
# Might abort...
AM_PATH_GTK([1.0.2], [], [AC_MSG_ERROR([GTK not in path])])
AM_PATH_GTKMM([0.9.5], [], [AC_MSG_ERROR([GTK not in path])])
... AC_OUTPUT, etc. ...

File: autoconf.info, Node: Printing Messages, Prev: Caching Results, Up: Results
7.5 Printing Messages
=====================
`configure' scripts need to give users running them several kinds of
information. The following macros print messages in ways appropriate
for each kind. The arguments to all of them get enclosed in shell
double quotes, so the shell performs variable and back-quote
substitution on them.
These macros are all wrappers around the `echo' shell command. They
direct output to the appropriate file descriptor (*note File Descriptor
Macros::). `configure' scripts should rarely need to run `echo'
directly to print messages for the user. Using these macros makes it
easy to change how and when each kind of message is printed; such
changes need only be made to the macro definitions and all the callers
change automatically.
To diagnose static issues, i.e., when `autoconf' is run, see *Note
Reporting Messages::.
-- Macro: AC_MSG_CHECKING (FEATURE-DESCRIPTION)
Notify the user that `configure' is checking for a particular
feature. This macro prints a message that starts with `checking '
and ends with `...' and no newline. It must be followed by a call
to `AC_MSG_RESULT' to print the result of the check and the
newline. The FEATURE-DESCRIPTION should be something like
`whether the Fortran compiler accepts C++ comments' or `for c89'.
This macro prints nothing if `configure' is run with the `--quiet'
or `--silent' option.
-- Macro: AC_MSG_RESULT (RESULT-DESCRIPTION)
Notify the user of the results of a check. RESULT-DESCRIPTION is
almost always the value of the cache variable for the check,
typically `yes', `no', or a file name. This macro should follow a
call to `AC_MSG_CHECKING', and the RESULT-DESCRIPTION should be
the completion of the message printed by the call to
`AC_MSG_CHECKING'.
This macro prints nothing if `configure' is run with the `--quiet'
or `--silent' option.
-- Macro: AC_MSG_NOTICE (MESSAGE)
Deliver the MESSAGE to the user. It is useful mainly to print a
general description of the overall purpose of a group of feature
checks, e.g.,
AC_MSG_NOTICE([checking if stack overflow is detectable])
This macro prints nothing if `configure' is run with the `--quiet'
or `--silent' option.
-- Macro: AC_MSG_ERROR (ERROR-DESCRIPTION, [EXIT-STATUS])
Notify the user of an error that prevents `configure' from
completing. This macro prints an error message to the standard
error output and exits `configure' with EXIT-STATUS (1 by default).
ERROR-DESCRIPTION should be something like `invalid value $HOME
for \$HOME'.
The ERROR-DESCRIPTION should start with a lower-case letter, and
"cannot" is preferred to "can't".
-- Macro: AC_MSG_FAILURE (ERROR-DESCRIPTION, [EXIT-STATUS])
This `AC_MSG_ERROR' wrapper notifies the user of an error that
prevents `configure' from completing _and_ that additional details
are provided in `config.log'. This is typically used when
abnormal results are found during a compilation.
-- Macro: AC_MSG_WARN (PROBLEM-DESCRIPTION)
Notify the `configure' user of a possible problem. This macro
prints the message to the standard error output; `configure'
continues running afterward, so macros that call `AC_MSG_WARN'
should provide a default (back-up) behavior for the situations
they warn about. PROBLEM-DESCRIPTION should be something like `ln
-s seems to make hard links'.

File: autoconf.info, Node: Programming in M4, Next: Writing Autoconf Macros, Prev: Results, Up: Top
8 Programming in M4
*******************
Autoconf is written on top of two layers: "M4sugar", which provides
convenient macros for pure M4 programming, and "M4sh", which provides
macros dedicated to shell script generation.
As of this version of Autoconf, these two layers are still
experimental, and their interface might change in the future. As a
matter of fact, _anything that is not documented must not be used_.
* Menu:
* M4 Quotation:: Protecting macros from unwanted expansion
* Using autom4te:: The Autoconf executables backbone
* Programming in M4sugar:: Convenient pure M4 macros
* Programming in M4sh:: Common shell Constructs
* File Descriptor Macros:: File descriptor macros for input and output

File: autoconf.info, Node: M4 Quotation, Next: Using autom4te, Up: Programming in M4
8.1 M4 Quotation
================
The most common problem with existing macros is an improper quotation.
This section, which users of Autoconf can skip, but which macro writers
_must_ read, first justifies the quotation scheme that was chosen for
Autoconf and then ends with a rule of thumb. Understanding the former
helps one to follow the latter.
* Menu:
* Active Characters:: Characters that change the behavior of M4
* One Macro Call:: Quotation and one macro call
* Quotation and Nested Macros:: Macros calling macros
* Changequote is Evil:: Worse than INTERCAL: M4 + changequote
* Quadrigraphs:: Another way to escape special characters
* Quotation Rule Of Thumb:: One parenthesis, one quote

File: autoconf.info, Node: Active Characters, Next: One Macro Call, Up: M4 Quotation
8.1.1 Active Characters
-----------------------
To fully understand where proper quotation is important, you first need
to know what the special characters are in Autoconf: `#' introduces a
comment inside which no macro expansion is performed, `,' separates
arguments, `[' and `]' are the quotes themselves, and finally `(' and
`)' (which M4 tries to match by pairs).
In order to understand the delicate case of macro calls, we first
have to present some obvious failures. Below they are "obvious-ified",
but when you find them in real life, they are usually in disguise.
Comments, introduced by a hash and running up to the newline, are
opaque tokens to the top level: active characters are turned off, and
there is no macro expansion:
# define([def], ine)
=># define([def], ine)
Each time there can be a macro expansion, there is a quotation
expansion, i.e., one level of quotes is stripped:
int tab[10];
=>int tab10;
[int tab[10];]
=>int tab[10];
Without this in mind, the reader might try hopelessly to use her
macro `array':
define([array], [int tab[10];])
array
=>int tab10;
[array]
=>array
How can you correctly output the intended results(1)?
---------- Footnotes ----------
(1) Using `defn'.

File: autoconf.info, Node: One Macro Call, Next: Quotation and Nested Macros, Prev: Active Characters, Up: M4 Quotation
8.1.2 One Macro Call
--------------------
Let's proceed on the interaction between active characters and macros
with this small macro, which just returns its first argument:
define([car], [$1])
The two pairs of quotes above are not part of the arguments of
`define'; rather, they are understood by the top level when it tries to
find the arguments of `define'. Therefore, assuming `car' is not
already defined, it is equivalent to write:
define(car, $1)
But, while it is acceptable for a `configure.ac' to avoid unnecessary
quotes, it is bad practice for Autoconf macros which must both be more
robust and also advocate perfect style.
At the top level, there are only two possibilities: either you quote
or you don't:
car(foo, bar, baz)
=>foo
[car(foo, bar, baz)]
=>car(foo, bar, baz)
Let's pay attention to the special characters:
car(#)
error-->EOF in argument list
The closing parenthesis is hidden in the comment; with a hypothetical
quoting, the top level understood it this way:
car([#)]
Proper quotation, of course, fixes the problem:
car([#])
=>#
Here are more examples:
car(foo, bar)
=>foo
car([foo, bar])
=>foo, bar
car((foo, bar))
=>(foo, bar)
car([(foo], [bar)])
=>(foo
define([a], [b])
=>
car(a)
=>b
car([a])
=>b
car([[a]])
=>a
car([[[a]]])
=>[a]
With this in mind, we can explore the cases where macros invoke
macros....

File: autoconf.info, Node: Quotation and Nested Macros, Next: Changequote is Evil, Prev: One Macro Call, Up: M4 Quotation
8.1.3 Quotation and Nested Macros
---------------------------------
The examples below use the following macros:
define([car], [$1])
define([active], [ACT, IVE])
define([array], [int tab[10]])
Each additional embedded macro call introduces other possible
interesting quotations:
car(active)
=>ACT
car([active])
=>ACT, IVE
car([[active]])
=>active
In the first case, the top level looks for the arguments of `car',
and finds `active'. Because M4 evaluates its arguments before applying
the macro, `active' is expanded, which results in:
car(ACT, IVE)
=>ACT
In the second case, the top level gives `active' as first and only
argument of `car', which results in:
active
=>ACT, IVE
i.e., the argument is evaluated _after_ the macro that invokes it. In
the third case, `car' receives `[active]', which results in:
[active]
=>active
exactly as we already saw above.
The example above, applied to a more realistic example, gives:
car(int tab[10];)
=>int tab10;
car([int tab[10];])
=>int tab10;
car([[int tab[10];]])
=>int tab[10];
Huh? The first case is easily understood, but why is the second wrong,
and the third right? To understand that, you must know that after M4
expands a macro, the resulting text is immediately subjected to macro
expansion and quote removal. This means that the quote removal occurs
twice--first before the argument is passed to the `car' macro, and
second after the `car' macro expands to the first argument.
As the author of the Autoconf macro `car', you then consider it to
be incorrect that your users have to double-quote the arguments of
`car', so you "fix" your macro. Let's call it `qar' for quoted car:
define([qar], [[$1]])
and check that `qar' is properly fixed:
qar([int tab[10];])
=>int tab[10];
Ahhh! That's much better.
But note what you've done: now that the arguments are literal
strings, if the user wants to use the results of expansions as
arguments, she has to use an _unquoted_ macro call:
qar(active)
=>ACT
where she wanted to reproduce what she used to do with `car':
car([active])
=>ACT, IVE
Worse yet: she wants to use a macro that produces a set of `cpp' macros:
define([my_includes], [#include <stdio.h>])
car([my_includes])
=>#include <stdio.h>
qar(my_includes)
error-->EOF in argument list
This macro, `qar', because it double quotes its arguments, forces
its users to leave their macro calls unquoted, which is dangerous.
Commas and other active symbols are interpreted by M4 before they are
given to the macro, often not in the way the users expect. Also,
because `qar' behaves differently from the other macros, it's an
exception that should be avoided in Autoconf.

File: autoconf.info, Node: Changequote is Evil, Next: Quadrigraphs, Prev: Quotation and Nested Macros, Up: M4 Quotation
8.1.4 `changequote' is Evil
---------------------------
The temptation is often high to bypass proper quotation, in particular
when it's late at night. Then, many experienced Autoconf hackers
finally surrender to the dark side of the force and use the ultimate
weapon: `changequote'.
The M4 builtin `changequote' belongs to a set of primitives that
allow one to adjust the syntax of the language to adjust it to one's
needs. For instance, by default M4 uses ``' and `'' as quotes, but in
the context of shell programming (and actually of most programming
languages), that's about the worst choice one can make: because of
strings and back-quoted expressions in shell code (such as `'this'' and
``that`'), because of literal characters in usual programming languages
(as in `'0''), there are many unbalanced ``' and `''. Proper M4
quotation then becomes a nightmare, if not impossible. In order to
make M4 useful in such a context, its designers have equipped it with
`changequote', which makes it possible to choose another pair of
quotes. M4sugar, M4sh, Autoconf, and Autotest all have chosen to use
`[' and `]'. Not especially because they are unlikely characters, but
_because they are characters unlikely to be unbalanced_.
There are other magic primitives, such as `changecom' to specify
what syntactic forms are comments (it is common to see `changecom(<!--,
-->)' when M4 is used to produce HTML pages), `changeword' and
`changesyntax' to change other syntactic details (such as the character
to denote the Nth argument, `$' by default, the parenthesis around
arguments, etc.).
These primitives are really meant to make M4 more useful for specific
domains: they should be considered like command line options:
`--quotes', `--comments', `--words', and `--syntax'. Nevertheless,
they are implemented as M4 builtins, as it makes M4 libraries self
contained (no need for additional options).
There lies the problem....
The problem is that it is then tempting to use them in the middle of
an M4 script, as opposed to its initialization. This, if not carefully
thought out, can lead to disastrous effects: _you are changing the
language in the middle of the execution_. Changing and restoring the
syntax is often not enough: if you happened to invoke macros in between,
these macros are lost, as the current syntax is probably not the one
they were implemented with.

File: autoconf.info, Node: Quadrigraphs, Next: Quotation Rule Of Thumb, Prev: Changequote is Evil, Up: M4 Quotation
8.1.5 Quadrigraphs
------------------
When writing an Autoconf macro you may occasionally need to generate
special characters that are difficult to express with the standard
Autoconf quoting rules. For example, you may need to output the regular
expression `[^[]', which matches any character other than `['. This
expression contains unbalanced brackets so it cannot be put easily into
an M4 macro.
You can work around this problem by using one of the following
"quadrigraphs":
`@<:@'
`['
`@:>@'
`]'
`@S|@'
`$'
`@%:@'
`#'
`@&t@'
Expands to nothing.
Quadrigraphs are replaced at a late stage of the translation process,
after `m4' is run, so they do not get in the way of M4 quoting. For
example, the string `^@<:@', independently of its quotation, appears as
`^[' in the output.
The empty quadrigraph can be used:
- to mark trailing spaces explicitly
Trailing spaces are smashed by `autom4te'. This is a feature.
- to produce other quadrigraphs
For instance `@<@&t@:@' produces `@<:@'.
- to escape _occurrences_ of forbidden patterns
For instance you might want to mention `AC_FOO' in a comment, while
still being sure that `autom4te' still catches unexpanded `AC_*'.
Then write `AC@&t@_FOO'.
The name `@&t@' was suggested by Paul Eggert:
I should give some credit to the `@&t@' pun. The `&' is my own
invention, but the `t' came from the source code of the ALGOL68C
compiler, written by Steve Bourne (of Bourne shell fame), and
which used `mt' to denote the empty string. In C, it would have
looked like something like:
char const mt[] = "";
but of course the source code was written in Algol 68.
I don't know where he got `mt' from: it could have been his own
invention, and I suppose it could have been a common pun around the
Cambridge University computer lab at the time.

File: autoconf.info, Node: Quotation Rule Of Thumb, Prev: Quadrigraphs, Up: M4 Quotation
8.1.6 Quotation Rule Of Thumb
-----------------------------
To conclude, the quotation rule of thumb is:
_One pair of quotes per pair of parentheses._
Never over-quote, never under-quote, in particular in the definition
of macros. In the few places where the macros need to use brackets
(usually in C program text or regular expressions), properly quote _the
arguments_!
It is common to read Autoconf programs with snippets like:
AC_TRY_LINK(
changequote(<<, >>)dnl
<<#include <time.h>
#ifndef tzname /* For SGI. */
extern char *tzname[]; /* RS6000 and others reject char **tzname. */
#endif>>,
changequote([, ])dnl
[atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no)
which is incredibly useless since `AC_TRY_LINK' is _already_ double
quoting, so you just need:
AC_TRY_LINK(
[#include <time.h>
#ifndef tzname /* For SGI. */
extern char *tzname[]; /* RS6000 and others reject char **tzname. */
#endif],
[atoi (*tzname);],
[ac_cv_var_tzname=yes],
[ac_cv_var_tzname=no])
The M4-fluent reader might note that these two examples are rigorously
equivalent, since M4 swallows both the `changequote(<<, >>)' and `<<'
`>>' when it "collects" the arguments: these quotes are not part of the
arguments!
Simplified, the example above is just doing this:
changequote(<<, >>)dnl
<<[]>>
changequote([, ])dnl
instead of simply:
[[]]
With macros that do not double quote their arguments (which is the
rule), double-quote the (risky) literals:
AC_LINK_IFELSE([AC_LANG_PROGRAM(
[[#include <time.h>
#ifndef tzname /* For SGI. */
extern char *tzname[]; /* RS6000 and others reject char **tzname. */
#endif]],
[atoi (*tzname);])],
[ac_cv_var_tzname=yes],
[ac_cv_var_tzname=no])
Please note that the macro `AC_TRY_LINK' is obsolete, so you really
should be using `AC_LINK_IFELSE' instead.
*Note Quadrigraphs::, for what to do if you run into a hopeless case
where quoting does not suffice.
When you create a `configure' script using newly written macros,
examine it carefully to check whether you need to add more quotes in
your macros. If one or more words have disappeared in the M4 output,
you need more quotes. When in doubt, quote.
However, it's also possible to put on too many layers of quotes. If
this happens, the resulting `configure' script may contain unexpanded
macros. The `autoconf' program checks for this problem by looking for
the string `AC_' in `configure'. However, this heuristic does not work
in general: for example, it does not catch overquoting in `AC_DEFINE'
descriptions.

File: autoconf.info, Node: Using autom4te, Next: Programming in M4sugar, Prev: M4 Quotation, Up: Programming in M4
8.2 Using `autom4te'
====================
The Autoconf suite, including M4sugar, M4sh, and Autotest, in addition
to Autoconf per se, heavily rely on M4. All these different uses
revealed common needs factored into a layer over M4: `autom4te'(1).
`autom4te' is a preprocessor that is like `m4'. It supports M4
extensions designed for use in tools like Autoconf.
* Menu:
* autom4te Invocation:: A GNU M4 wrapper
* Customizing autom4te:: Customizing the Autoconf package
---------- Footnotes ----------
(1) Yet another great name from Lars J. Aas.

File: autoconf.info, Node: autom4te Invocation, Next: Customizing autom4te, Up: Using autom4te
8.2.1 Invoking `autom4te'
-------------------------
The command line arguments are modeled after M4's:
autom4te OPTIONS FILES
where the FILES are directly passed to `m4'. By default, GNU M4 is
found during configuration, but the environment variable `M4' can be
set to tell `autom4te' where to look. In addition to the regular
expansion, it handles the replacement of the quadrigraphs (*note
Quadrigraphs::), and of `__oline__', the current line in the output.
It supports an extended syntax for the FILES:
`FILE.m4f'
This file is an M4 frozen file. Note that _all the previous files
are ignored_. See the option `--melt' for the rationale.
`FILE?'
If found in the library path, the FILE is included for expansion,
otherwise it is ignored instead of triggering a failure.
Of course, it supports the Autoconf common subset of options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files and be even more verbose.
`--include=DIR'
`-I DIR'
Also look for input files in DIR. Multiple invocations accumulate.
`--output=FILE'
`-o FILE'
Save output (script or trace) to FILE. The file `-' stands for
the standard output.
As an extension of `m4', it includes the following options:
`--warnings=CATEGORY'
`-W CATEGORY'
Report the warnings related to CATEGORY (which can actually be a
comma separated list). *Note Reporting Messages::, macro
`AC_DIAGNOSE', for a comprehensive list of categories. Special
values include:
`all'
report all the warnings
`none'
report none
`error'
treats warnings as errors
`no-CATEGORY'
disable warnings falling into CATEGORY
Warnings about `syntax' are enabled by default, and the environment
variable `WARNINGS', a comma separated list of categories, is
honored. `autom4te -W CATEGORY' actually behaves as if you had
run:
autom4te --warnings=syntax,$WARNINGS,CATEGORY
For example, if you want to disable defaults and `WARNINGS' of
`autom4te', but enable the warnings about obsolete constructs, you
would use `-W none,obsolete'.
`autom4te' displays a back trace for errors, but not for warnings;
if you want them, just pass `-W error'.
`--melt'
`-M'
Do not use frozen files. Any argument `FILE.m4f' is replaced by
`FILE.m4'. This helps tracing the macros which are executed only
when the files are frozen, typically `m4_define'. For instance,
running:
autom4te --melt 1.m4 2.m4f 3.m4 4.m4f input.m4
is roughly equivalent to running:
m4 1.m4 2.m4 3.m4 4.m4 input.m4
while
autom4te 1.m4 2.m4f 3.m4 4.m4f input.m4
is equivalent to:
m4 --reload-state=4.m4f input.m4
`--freeze'
`-f'
Produce a frozen state file. `autom4te' freezing is stricter than
M4's: it must produce no warnings, and no output other than empty
lines (a line with white space is _not_ empty) and comments
(starting with `#'). Unlike `m4''s similarly-named option, this
option takes no argument:
autom4te 1.m4 2.m4 3.m4 --freeze --output=3.m4f
corresponds to
m4 1.m4 2.m4 3.m4 --freeze-state=3.m4f
`--mode=OCTAL-MODE'
`-m OCTAL-MODE'
Set the mode of the non-traces output to OCTAL-MODE; by default
`0666'.
As another additional feature over `m4', `autom4te' caches its
results. GNU M4 is able to produce a regular output and traces at the
same time. Traces are heavily used in the GNU Build System:
`autoheader' uses them to build `config.h.in', `autoreconf' to
determine what GNU Build System components are used, `automake' to
"parse" `configure.ac' etc. To avoid recomputation, traces are cached
while performing regular expansion, and conversely. This cache is
(actually, the caches are) stored in the directory `autom4te.cache'.
_It can safely be removed_ at any moment (especially if for some reason
`autom4te' considers it is trashed).
`--cache=DIRECTORY'
`-C DIRECTORY'
Specify the name of the directory where the result should be
cached. Passing an empty value disables caching. Be sure to pass
a relative file name, as for the time being, global caches are not
supported.
`--no-cache'
Don't cache the results.
`--force'
`-f'
If a cache is used, consider it obsolete (but update it anyway).
Because traces are so important to the GNU Build System, `autom4te'
provides high level tracing features as compared to M4, and helps
exploiting the cache:
`--trace=MACRO[:FORMAT]'
`-t MACRO[:FORMAT]'
Trace the invocations of MACRO according to the FORMAT. Multiple
`--trace' arguments can be used to list several macros. Multiple
`--trace' arguments for a single macro are not cumulative;
instead, you should just make FORMAT as long as needed.
The FORMAT is a regular string, with newlines if desired, and
several special escape codes. It defaults to `$f:$l:$n:$%'. It
can use the following special escapes:
`$$'
The character `$'.
`$f'
The file name from which MACRO is called.
`$l'
The line number from which MACRO is called.
`$d'
The depth of the MACRO call. This is an M4 technical detail
that you probably don't want to know about.
`$n'
The name of the MACRO.
`$NUM'
The NUMth argument of the call to MACRO.
`$@'
`$SEP@'
`${SEPARATOR}@'
All the arguments passed to MACRO, separated by the character
SEP or the string SEPARATOR (`,' by default). Each argument
is quoted, i.e., enclosed in a pair of square brackets.
`$*'
`$SEP*'
`${SEPARATOR}*'
As above, but the arguments are not quoted.
`$%'
`$SEP%'
`${SEPARATOR}%'
As above, but the arguments are not quoted, all new line
characters in the arguments are smashed, and the default
separator is `:'.
The escape `$%' produces single-line trace outputs (unless
you put newlines in the `separator'), while `$@' and `$*' do
not.
*Note autoconf Invocation::, for examples of trace uses.
`--preselect=MACRO'
`-p MACRO'
Cache the traces of MACRO, but do not enable traces. This is
especially important to save CPU cycles in the future. For
instance, when invoked, `autoconf' preselects all the macros that
`autoheader', `automake', `autoreconf', etc., trace, so that
running `m4' is not needed to trace them: the cache suffices.
This results in a huge speed-up.
Finally, `autom4te' introduces the concept of "Autom4te libraries".
They consists in a powerful yet extremely simple feature: sets of
combined command line arguments:
`--language=LANGUAGE'
`-l LANGUAGE'
Use the LANGUAGE Autom4te library. Current languages include:
`M4sugar'
create M4sugar output.
`M4sh'
create M4sh executable shell scripts.
`Autotest'
create Autotest executable test suites.
`Autoconf-without-aclocal-m4'
create Autoconf executable configure scripts without reading
`aclocal.m4'.
`Autoconf'
create Autoconf executable configure scripts. This language
inherits all the characteristics of
`Autoconf-without-aclocal-m4' and additionally reads
`aclocal.m4'.
`--prepend-include=DIR'
`-B DIR'
Prepend directory DIR to the search path. This is used to include
the language-specific files before any third-party macros.
As an example, if Autoconf is installed in its default location,
`/usr/local', the command `autom4te -l m4sugar foo.m4' is strictly
equivalent to the command:
autom4te --prepend-include /usr/local/share/autoconf \
m4sugar/m4sugar.m4f --warnings syntax foo.m4
Recursive expansion applies here: the command `autom4te -l m4sh foo.m4'
is the same as `autom4te --language M4sugar m4sugar/m4sh.m4f foo.m4',
i.e.:
autom4te --prepend-include /usr/local/share/autoconf \
m4sugar/m4sugar.m4f m4sugar/m4sh.m4f --mode 777 foo.m4
The definition of the languages is stored in `autom4te.cfg'.

File: autoconf.info, Node: Customizing autom4te, Prev: autom4te Invocation, Up: Using autom4te
8.2.2 Customizing `autom4te'
----------------------------
One can customize `autom4te' via `~/.autom4te.cfg' (i.e., as found in
the user home directory), and `./.autom4te.cfg' (i.e., as found in the
directory from which `autom4te' is run). The order is first reading
`autom4te.cfg', then `~/.autom4te.cfg', then `./.autom4te.cfg', and
finally the command line arguments.
In these text files, comments are introduced with `#', and empty
lines are ignored. Customization is performed on a per-language basis,
wrapped in between a `begin-language: "LANGUAGE"', `end-language:
"LANGUAGE"' pair.
Customizing a language stands for appending options (*note autom4te
Invocation::) to the current definition of the language. Options, and
more generally arguments, are introduced by `args: ARGUMENTS'. You may
use the traditional shell syntax to quote the ARGUMENTS.
As an example, to disable Autoconf caches (`autom4te.cache')
globally, include the following lines in `~/.autom4te.cfg':
## ------------------ ##
## User Preferences. ##
## ------------------ ##
begin-language: "Autoconf-without-aclocal-m4"
args: --no-cache
end-language: "Autoconf-without-aclocal-m4"

File: autoconf.info, Node: Programming in M4sugar, Next: Programming in M4sh, Prev: Using autom4te, Up: Programming in M4
8.3 Programming in M4sugar
==========================
M4 by itself provides only a small, but sufficient, set of all-purpose
macros. M4sugar introduces additional generic macros. Its name was
coined by Lars J. Aas: "Readability And Greater Understanding Stands 4
M4sugar".
* Menu:
* Redefined M4 Macros:: M4 builtins changed in M4sugar
* Looping constructs:: Iteration in M4
* Evaluation Macros:: More quotation and evaluation control
* Text processing Macros:: String manipulation in M4
* Forbidden Patterns:: Catching unexpanded macros

File: autoconf.info, Node: Redefined M4 Macros, Next: Looping constructs, Up: Programming in M4sugar
8.3.1 Redefined M4 Macros
-------------------------
With a few exceptions, all the M4 native macros are moved in the `m4_'
pseudo-namespace, e.g., M4sugar renames `define' as `m4_define' etc.
Some M4 macros are redefined, and are slightly incompatible with
their native equivalent.
-- Macro: dnl
This macro kept its original name: no `m4_dnl' is defined.
-- Macro: m4_defn (MACRO)
Unlike the M4 builtin, this macro fails if MACRO is not defined.
See `m4_undefine'.
-- Macro: m4_exit (EXIT-STATUS)
This macro corresponds to `m4exit'.
-- Macro: m4_if (COMMENT)
-- Macro: m4_if (STRING-1, STRING-2, EQUAL, [NOT-EQUAL])
-- Macro: m4_if (STRING-1, STRING-2, EQUAL, ...)
This macro corresponds to `ifelse'.
-- Macro: m4_include (FILE)
-- Macro: m4_sinclude (FILE)
Like the M4 builtins, but warn against multiple inclusions of FILE.
-- Macro: m4_bpatsubst (STRING, REGEXP, [REPLACEMENT])
This macro corresponds to `patsubst'. The name `m4_patsubst' is
kept for future versions of M4sh, on top of GNU M4 which will
provide extended regular expression syntax via `epatsubst'.
-- Macro: m4_popdef (MACRO)
Unlike the M4 builtin, this macro fails if MACRO is not defined.
See `m4_undefine'.
-- Macro: m4_bregexp (STRING, REGEXP, [REPLACEMENT])
This macro corresponds to `regexp'. The name `m4_regexp' is kept
for future versions of M4sh, on top of GNU M4 which will provide
extended regular expression syntax via `eregexp'.
-- Macro: m4_wrap (TEXT)
This macro corresponds to `m4wrap'.
Posix requires arguments of multiple `m4wrap' calls to be
reprocessed at EOF in the same order as the original calls. GNU
M4 versions through 1.4.x, however, reprocess them in reverse
order. Your code should not depend on the order.
Also, Posix requires `m4wrap' to ignore its second and succeeding
arguments, but GNU M4 versions through 1.4.x concatenate the
arguments with intervening spaces. Your code should not pass more
than one argument.
You are encouraged to end TEXT with `[]', to avoid unexpected
token pasting between consecutive invocations of `m4_wrap', as in:
m4_define([foo], [bar])
m4_define([foofoo], [OUCH])
m4_wrap([foo])
m4_wrap([foo])
=>OUCH
-- Macro: m4_undefine (MACRO)
Unlike the M4 builtin, this macro fails if MACRO is not defined.
Use
m4_ifdef([MACRO], [m4_undefine([MACRO])])
to recover the behavior of the builtin.
-- Macro: m4_maketemp (TEMPLATE)
-- Macro: m4_mkstemp (TEMPLATE)
Posix requires `maketemp' to replace the trailing `X' characters
in TEMPLATE with the process id, without regards to the existence
of a file by that name, but this a security hole. When this was
pointed out to the Posix folks, they agreed to invent a new macro
`mkstemp' that always creates a uniquely named file, but not all
versions of GNU M4 support the new macro. In M4sugar,
`m4_maketemp' and `m4_mkstemp' are synonyms for each other, and
both have the secure semantics regardless of which macro the
underlying M4 provides.

File: autoconf.info, Node: Looping constructs, Next: Evaluation Macros, Prev: Redefined M4 Macros, Up: Programming in M4sugar
8.3.2 Looping constructs
------------------------
The following macros implement loops in M4.
-- Macro: m4_for (VAR, FIRST, LAST, [STEP], EXPRESSION)
Loop over the numeric values between FIRST and LAST including
bounds by increments of STEP. For each iteration, expand
EXPRESSION with the numeric value assigned to VAR. If STEP is
omitted, it defaults to `1' or `-1' depending on the order of the
limits. If given, STEP has to match this order.
-- Macro: m4_foreach (VAR, LIST, EXPRESSION)
Loop over the comma-separated M4 list LIST, assigning each value
to VAR, and expand EXPRESSION. The following example outputs two
lines:
m4_foreach([myvar], [[foo], [bar, baz]],
[echo myvar
])
-- Macro: m4_foreach_w (VAR, LIST, EXPRESSION)
Loop over the white-space-separated list LIST, assigning each value
to VAR, and expand EXPRESSION.
The deprecated macro `AC_FOREACH' is an alias of `m4_foreach_w'.

File: autoconf.info, Node: Evaluation Macros, Next: Text processing Macros, Prev: Looping constructs, Up: Programming in M4sugar
8.3.3 Evaluation Macros
-----------------------
The following macros give some control over the order of the evaluation
by adding or removing levels of quotes. They are meant for hard-core M4
programmers.
-- Macro: m4_dquote (ARG1, ...)
Return the arguments as a quoted list of quoted arguments.
-- Macro: m4_quote (ARG1, ...)
Return the arguments as a single entity, i.e., wrap them into a
pair of quotes.
The following example aims at emphasizing the difference between
(i), not using these macros, (ii), using `m4_quote', and (iii), using
`m4_dquote'.
$ cat example.m4
# Overquote, so that quotes are visible.
m4_define([show], [$[]1 = [$1], $[]@ = [$@]])
m4_define([mkargs], [1, 2, 3])
m4_define([arg1], [[$1]])
m4_divert(0)dnl
show(a, b)
show(m4_quote(a, b))
show(m4_dquote(a, b))
arg1(mkargs)
arg1([mkargs])
arg1(m4_defn([mkargs]))
arg1(m4_quote(mkargs))
arg1(m4_dquote(mkargs))
$ autom4te -l m4sugar example.m4
$1 = a, $@ = [a],[b]
$1 = a,b, $@ = [a,b]
$1 = [a],[b], $@ = [[a],[b]]
1
mkargs
1, 2, 3
1,2,3
[1],[2],[3]

File: autoconf.info, Node: Text processing Macros, Next: Forbidden Patterns, Prev: Evaluation Macros, Up: Programming in M4sugar
8.3.4 Text processing Macros
----------------------------
The following macros may be used to manipulate strings in M4. They are
not intended for casual use.
-- Macro: m4_re_escape (STRING)
Backslash-escape all characters in STRING that are active in
regexps.
-- Macro: m4_tolower (STRING)
-- Macro: m4_toupper (STRING)
Return STRING with letters converted to upper or lower case,
respectively.
-- Macro: m4_split (STRING, [REGEXP])
Split STRING into an M4 list of elements quoted by `[' and `]',
while keeping white space at the beginning and at the end. If
REGEXP is given, use it instead of `[\t ]+' for splitting. If
STRING is empty, the result is an empty list.
-- Macro: m4_normalize (STRING)
Remove leading and trailing spaces and tabs, sequences of
backslash-then-newline, and replace multiple spaces and tabs with a
single space.
-- Macro: m4_append (MACRO-NAME, STRING, [SEPARATOR])
-- Macro: m4_append_uniq (MACRO-NAME, STRING, [SEPARATOR])
Redefine MACRO-NAME to its former contents with SEPARATOR and
STRING added at the end. If MACRO-NAME was undefined before (but
not if it was defined but empty), then no SEPARATOR is added.
`m4_append' can be used to grow strings, and `m4_append_uniq' to
grow strings without duplicating substrings.

File: autoconf.info, Node: Forbidden Patterns, Prev: Text processing Macros, Up: Programming in M4sugar
8.3.5 Forbidden Patterns
------------------------
M4sugar provides a means to define suspicious patterns, patterns
describing tokens which should not be found in the output. For
instance, if an Autoconf `configure' script includes tokens such as
`AC_DEFINE', or `dnl', then most probably something went wrong
(typically a macro was not evaluated because of overquotation).
M4sugar forbids all the tokens matching `^m4_' and `^dnl$'.
-- Macro: m4_pattern_forbid (PATTERN)
Declare that no token matching PATTERN must be found in the output.
Comments are not checked; this can be a problem if, for instance,
you have some macro left unexpanded after an `#include'. No
consensus is currently found in the Autoconf community, as some
people consider it should be valid to name macros in comments
(which doesn't make sense to the author of this documentation, as
`#'-comments should document the output, not the input, documented
by `dnl' comments).
Of course, you might encounter exceptions to these generic rules, for
instance you might have to refer to `$m4_flags'.
-- Macro: m4_pattern_allow (PATTERN)
Any token matching PATTERN is allowed, including if it matches an
`m4_pattern_forbid' pattern.

File: autoconf.info, Node: Programming in M4sh, Next: File Descriptor Macros, Prev: Programming in M4sugar, Up: Programming in M4
8.4 Programming in M4sh
=======================
M4sh, pronounced "mash", is aiming at producing portable Bourne shell
scripts. This name was coined by Lars J. Aas, who notes that,
according to the Webster's Revised Unabridged Dictionary (1913):
Mash \Mash\, n. [Akin to G. meisch, maisch, meische, maische,
mash, wash, and prob. to AS. miscian to mix. See "Mix".]
1. A mass of mixed ingredients reduced to a soft pulpy state by
beating or pressure....
2. A mixture of meal or bran and water fed to animals.
3. A mess; trouble. [Obs.] -Beau. & Fl.
For the time being, it is not mature enough to be widely used.
M4sh provides portable alternatives for some common shell constructs
that unfortunately are not portable in practice.
-- Macro: AS_BOURNE_COMPATIBLE
Set up the shell to be more compatible with the Bourne shell as
standardized by Posix, if possible. This may involve setting
environment variables, or setting options, or similar
implementation-specific actions.
-- Macro: AS_CASE (WORD, [PATTERN1], [IF-MATCHED1], ..., [DEFAULT])
Expand into a shell `case' statement, where WORD is matched
against one or more patterns. IF-MATCHED is run if the
corresponding pattern matched WORD, else DEFAULT is run.
-- Macro: AS_DIRNAME (FILE-NAME)
Output the directory portion of FILE-NAME. For example, if
`$file' is `/one/two/three', the command
`dir=`AS_DIRNAME(["$file"])`' sets `dir' to `/one/two'.
-- Macro: AS_IF (TEST1, [RUN-IF-TRUE1], ..., [RUN-IF-FALSE])
Run shell code TEST1. If TEST1 exits with a zero status then run
shell code RUN-IF-TRUE1, else examine further tests. If no test
exits with a zero status, run shell code RUN-IF-FALSE, with
simplifications if either RUN-IF-TRUE1 or RUN-IF-FALSE1 is empty.
For example,
AS_IF([test "$foo" = yes], [HANDLE_FOO([yes])],
[test "$foo" != no], [HANDLE_FOO([maybe])],
[echo foo not specified])
ensures any required macros of `HANDLE_FOO' are expanded before
the first test.
-- Macro: AS_MKDIR_P (FILE-NAME)
Make the directory FILE-NAME, including intervening directories as
necessary. This is equivalent to `mkdir -p FILE-NAME', except
that it is portable to older versions of `mkdir' that lack support
for the `-p' option. Also, `AS_MKDIR_P' succeeds if FILE-NAME is
a symbolic link to an existing directory, even though Posix is
unclear whether `mkdir -p' should succeed in that case. If
creation of FILE-NAME fails, exit the script.
Also see the `AC_PROG_MKDIR_P' macro (*note Particular Programs::).
-- Macro: AS_SHELL_SANITIZE
Initialize the shell suitably for `configure' scripts. This has
the effect of `AS_BOURNE_COMPATIBLE', and sets some other
environment variables for predictable results from configuration
tests. For example, it sets `LC_ALL' to change to the default C
locale. *Note Special Shell Variables::.
-- Macro: AS_TR_CPP (EXPRESSION)
Transform EXPRESSION into a valid right-hand side for a C
`#define'. For example:
# This outputs "#define HAVE_CHAR_P 1".
type="char *"
echo "#define AS_TR_CPP([HAVE_$type]) 1"
-- Macro: AS_TR_SH (EXPRESSION)
Transform EXPRESSION into a valid shell variable name. For
example:
# This outputs "Have it!".
header="sys/some file.h"
AS_TR_SH([HAVE_$header])=yes
if test "$HAVE_sys_some_file_h" = yes; then echo "Have it!"; fi
-- Macro: AS_SET_CATFILE (VAR, DIR, FILE)
Set the shell variable VAR to DIR/FILE, but optimizing the common
cases (DIR or FILE is `.', FILE is absolute, etc.).

File: autoconf.info, Node: File Descriptor Macros, Prev: Programming in M4sh, Up: Programming in M4
8.5 File Descriptor Macros
==========================
The following macros define file descriptors used to output messages
(or input values) from `configure' scripts. For example:
echo "$wombats found" >&AS_MESSAGE_LOG_FD
echo 'Enter desired kangaroo count:' >&AS_MESSAGE_FD
read kangaroos <&AS_ORIGINAL_STDIN_FD`
However doing so is seldom needed, because Autoconf provides higher
level macros as described below.
-- Macro: AS_MESSAGE_FD
The file descriptor for `checking for...' messages and results.
Normally this directs messages to the standard output, however when
`configure' is run with the `-q' option, messages sent to
`AS_MESSAGE_FD' are discarded.
If you want to display some messages, consider using one of the
printing macros (*note Printing Messages::) instead. Copies of
messages output via these macros are also recorded in `config.log'.
-- Macro: AS_MESSAGE_LOG_FD
The file descriptor for messages logged to `config.log'. Macros
that run tools, like `AC_COMPILE_IFELSE' (*note Running the
Compiler::), redirect all output to this descriptor. You may want
to do so if you develop such a low-level macro.
-- Macro: AS_ORIGINAL_STDIN_FD
The file descriptor for the original standard input.
When `configure' runs, it may accidentally execute an interactive
command that has the same name as the non-interactive meant to be
used or checked. If the standard input was the terminal, such
interactive programs would cause `configure' to stop, pending some
user input. Therefore `configure' redirects its standard input
from `/dev/null' during its initialization. This is not normally
a problem, since `configure' normally does not need user input.
In the extreme case where your `configure' script really needs to
obtain some values from the original standard input, you can read
them explicitly from `AS_ORIGINAL_STDIN_FD'.

File: autoconf.info, Node: Writing Autoconf Macros, Next: Portable Shell, Prev: Programming in M4, Up: Top
9 Writing Autoconf Macros
*************************
When you write a feature test that could be applicable to more than one
software package, the best thing to do is encapsulate it in a new macro.
Here are some instructions and guidelines for writing Autoconf macros.
* Menu:
* Macro Definitions:: Basic format of an Autoconf macro
* Macro Names:: What to call your new macros
* Reporting Messages:: Notifying `autoconf' users
* Dependencies Between Macros:: What to do when macros depend on other macros
* Obsoleting Macros:: Warning about old ways of doing things
* Coding Style:: Writing Autoconf macros a` la Autoconf

File: autoconf.info, Node: Macro Definitions, Next: Macro Names, Up: Writing Autoconf Macros
9.1 Macro Definitions
=====================
Autoconf macros are defined using the `AC_DEFUN' macro, which is
similar to the M4 builtin `m4_define' macro. In addition to defining a
macro, `AC_DEFUN' adds to it some code that is used to constrain the
order in which macros are called (*note Prerequisite Macros::).
An Autoconf macro definition looks like this:
AC_DEFUN(MACRO-NAME, MACRO-BODY)
You can refer to any arguments passed to the macro as `$1', `$2',
etc. *Note How to define new macros: (m4.info)Definitions, for more
complete information on writing M4 macros.
Be sure to properly quote both the MACRO-BODY _and_ the MACRO-NAME
to avoid any problems if the macro happens to have been previously
defined.
Each macro should have a header comment that gives its prototype,
and a brief description. When arguments have default values, display
them in the prototype. For example:
# AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1])
# --------------------------------------
m4_define([AC_MSG_ERROR],
[{ AS_MESSAGE([error: $1], [2])
exit m4_default([$2], [1]); }])
Comments about the macro should be left in the header comment. Most
other comments make their way into `configure', so just keep using `#'
to introduce comments.
If you have some special comments about pure M4 code, comments that
make no sense in `configure' and in the header comment, then use the
builtin `dnl': it causes M4 to discard the text through the next
newline.
Keep in mind that `dnl' is rarely needed to introduce comments;
`dnl' is more useful to get rid of the newlines following macros that
produce no output, such as `AC_REQUIRE'.

File: autoconf.info, Node: Macro Names, Next: Reporting Messages, Prev: Macro Definitions, Up: Writing Autoconf Macros
9.2 Macro Names
===============
All of the Autoconf macros have all-uppercase names starting with `AC_'
to prevent them from accidentally conflicting with other text. All
shell variables that they use for internal purposes have
mostly-lowercase names starting with `ac_'. To ensure that your macros
don't conflict with present or future Autoconf macros, you should
prefix your own macro names and any shell variables they use with some
other sequence. Possibilities include your initials, or an abbreviation
for the name of your organization or software package.
Most of the Autoconf macros' names follow a structured naming
convention that indicates the kind of feature check by the name. The
macro names consist of several words, separated by underscores, going
from most general to most specific. The names of their cache variables
use the same convention (*note Cache Variable Names::, for more
information on them).
The first word of the name after `AC_' usually tells the category of
the feature being tested. Here are the categories used in Autoconf for
specific test macros, the kind of macro that you are more likely to
write. They are also used for cache variables, in all-lowercase. Use
them where applicable; where they're not, invent your own categories.
`C'
C language builtin features.
`DECL'
Declarations of C variables in header files.
`FUNC'
Functions in libraries.
`GROUP'
Posix group owners of files.
`HEADER'
Header files.
`LIB'
C libraries.
`PATH'
Absolute names of files, including programs.
`PROG'
The base names of programs.
`MEMBER'
Members of aggregates.
`SYS'
Operating system features.
`TYPE'
C builtin or declared types.
`VAR'
C variables in libraries.
After the category comes the name of the particular feature being
tested. Any further words in the macro name indicate particular aspects
of the feature. For example, `AC_PROG_CC_STDC' checks whether the C
compiler supports ISO Standard C.
An internal macro should have a name that starts with an underscore;
Autoconf internals should therefore start with `_AC_'. Additionally, a
macro that is an internal subroutine of another macro should have a
name that starts with an underscore and the name of that other macro,
followed by one or more words saying what the internal macro does. For
example, `AC_PATH_X' has internal macros `_AC_PATH_X_XMKMF' and
`_AC_PATH_X_DIRECT'.

File: autoconf.info, Node: Reporting Messages, Next: Dependencies Between Macros, Prev: Macro Names, Up: Writing Autoconf Macros
9.3 Reporting Messages
======================
When macros statically diagnose abnormal situations, benign or fatal,
they should report them using these macros. For dynamic issues, i.e.,
when `configure' is run, see *Note Printing Messages::.
-- Macro: AC_DIAGNOSE (CATEGORY, MESSAGE)
Report MESSAGE as a warning (or as an error if requested by the
user) if warnings of the CATEGORY are turned on. You are
encouraged to use standard categories, which currently include:
`all'
messages that don't fall into one of the following
categories. Use of an empty CATEGORY is equivalent.
`cross'
related to cross compilation issues.
`obsolete'
use of an obsolete construct.
`syntax'
dubious syntactic constructs, incorrectly ordered macro calls.
-- Macro: AC_WARNING (MESSAGE)
Equivalent to `AC_DIAGNOSE([syntax], MESSAGE)', but you are
strongly encouraged to use a finer grained category.
-- Macro: AC_FATAL (MESSAGE)
Report a severe error MESSAGE, and have `autoconf' die.
When the user runs `autoconf -W error', warnings from `AC_DIAGNOSE'
and `AC_WARNING' are reported as error, see *Note autoconf Invocation::.

File: autoconf.info, Node: Dependencies Between Macros, Next: Obsoleting Macros, Prev: Reporting Messages, Up: Writing Autoconf Macros
9.4 Dependencies Between Macros
===============================
Some Autoconf macros depend on other macros having been called first in
order to work correctly. Autoconf provides a way to ensure that certain
macros are called if needed and a way to warn the user if macros are
called in an order that might cause incorrect operation.
* Menu:
* Prerequisite Macros:: Ensuring required information
* Suggested Ordering:: Warning about possible ordering problems
* One-Shot Macros:: Ensuring a macro is called only once

File: autoconf.info, Node: Prerequisite Macros, Next: Suggested Ordering, Up: Dependencies Between Macros
9.4.1 Prerequisite Macros
-------------------------
A macro that you write might need to use values that have previously
been computed by other macros. For example, `AC_DECL_YYTEXT' examines
the output of `flex' or `lex', so it depends on `AC_PROG_LEX' having
been called first to set the shell variable `LEX'.
Rather than forcing the user of the macros to keep track of the
dependencies between them, you can use the `AC_REQUIRE' macro to do it
automatically. `AC_REQUIRE' can ensure that a macro is only called if
it is needed, and only called once.
-- Macro: AC_REQUIRE (MACRO-NAME)
If the M4 macro MACRO-NAME has not already been called, call it
(without any arguments). Make sure to quote MACRO-NAME with
square brackets. MACRO-NAME must have been defined using
`AC_DEFUN' or else contain a call to `AC_PROVIDE' to indicate that
it has been called.
`AC_REQUIRE' must be used inside a macro defined by `AC_DEFUN'; it
must not be called from the top level.
`AC_REQUIRE' is often misunderstood. It really implements
dependencies between macros in the sense that if one macro depends upon
another, the latter is expanded _before_ the body of the former. To be
more precise, the required macro is expanded before the outermost
defined macro in the current expansion stack. In particular,
`AC_REQUIRE([FOO])' is not replaced with the body of `FOO'. For
instance, this definition of macros:
AC_DEFUN([TRAVOLTA],
[test "$body_temperature_in_celsius" -gt "38" &&
dance_floor=occupied])
AC_DEFUN([NEWTON_JOHN],
[test "$hair_style" = "curly" &&
dance_floor=occupied])
AC_DEFUN([RESERVE_DANCE_FLOOR],
[if date | grep '^Sat.*pm' >/dev/null 2>&1; then
AC_REQUIRE([TRAVOLTA])
AC_REQUIRE([NEWTON_JOHN])
fi])
with this `configure.ac'
AC_INIT([Dance Manager], [1.0], [bug-dance@example.org])
RESERVE_DANCE_FLOOR
if test "$dance_floor" = occupied; then
AC_MSG_ERROR([cannot pick up here, let's move])
fi
does not leave you with a better chance to meet a kindred soul at other
times than Saturday night since it expands into:
test "$body_temperature_in_Celsius" -gt "38" &&
dance_floor=occupied
test "$hair_style" = "curly" &&
dance_floor=occupied
fi
if date | grep '^Sat.*pm' >/dev/null 2>&1; then
fi
This behavior was chosen on purpose: (i) it prevents messages in
required macros from interrupting the messages in the requiring macros;
(ii) it avoids bad surprises when shell conditionals are used, as in:
if ...; then
AC_REQUIRE([SOME_CHECK])
fi
...
SOME_CHECK
The helper macros `AS_IF' and `AS_CASE' may be used to enforce
expansion of required macros outside of shell conditional constructs.
You are furthermore encouraged to put all `AC_REQUIRE' calls at the
beginning of a macro. You can use `dnl' to avoid the empty lines they
leave.

File: autoconf.info, Node: Suggested Ordering, Next: One-Shot Macros, Prev: Prerequisite Macros, Up: Dependencies Between Macros
9.4.2 Suggested Ordering
------------------------
Some macros should be run before another macro if both are called, but
neither _requires_ that the other be called. For example, a macro that
changes the behavior of the C compiler should be called before any
macros that run the C compiler. Many of these dependencies are noted in
the documentation.
Autoconf provides the `AC_BEFORE' macro to warn users when macros
with this kind of dependency appear out of order in a `configure.ac'
file. The warning occurs when creating `configure' from
`configure.ac', not when running `configure'.
For example, `AC_PROG_CPP' checks whether the C compiler can run the
C preprocessor when given the `-E' option. It should therefore be
called after any macros that change which C compiler is being used,
such as `AC_PROG_CC'. So `AC_PROG_CC' contains:
AC_BEFORE([$0], [AC_PROG_CPP])dnl
This warns the user if a call to `AC_PROG_CPP' has already occurred
when `AC_PROG_CC' is called.
-- Macro: AC_BEFORE (THIS-MACRO-NAME, CALLED-MACRO-NAME)
Make M4 print a warning message to the standard error output if
CALLED-MACRO-NAME has already been called. THIS-MACRO-NAME should
be the name of the macro that is calling `AC_BEFORE'. The macro
CALLED-MACRO-NAME must have been defined using `AC_DEFUN' or else
contain a call to `AC_PROVIDE' to indicate that it has been called.

File: autoconf.info, Node: One-Shot Macros, Prev: Suggested Ordering, Up: Dependencies Between Macros
9.4.3 One-Shot Macros
---------------------
Some macros should be called only once, either because calling them
multiple time is unsafe, or because it is bad style. For instance
Autoconf ensures that `AC_CANONICAL_BUILD' and cousins (*note
Canonicalizing::) are evaluated only once, because it makes no sense to
run these expensive checks more than once. Such one-shot macros can be
defined using `AC_DEFUN_ONCE'.
-- Macro: AC_DEFUN_ONCE (MACRO-NAME, MACRO-BODY)
Declare macro MACRO-NAME like `AC_DEFUN' would (*note Macro
Definitions::), and emit a warning any time the macro is called
more than once.
Obviously it is not sensible to evaluate a macro defined by
`AC_DEFUN_ONCE' in a macro defined by `AC_DEFUN'. Most of the time you
want to use `AC_REQUIRE' (*note Prerequisite Macros::).

File: autoconf.info, Node: Obsoleting Macros, Next: Coding Style, Prev: Dependencies Between Macros, Up: Writing Autoconf Macros
9.5 Obsoleting Macros
=====================
Configuration and portability technology has evolved over the years.
Often better ways of solving a particular problem are developed, or
ad-hoc approaches are systematized. This process has occurred in many
parts of Autoconf. One result is that some of the macros are now
considered "obsolete"; they still work, but are no longer considered
the best thing to do, hence they should be replaced with more modern
macros. Ideally, `autoupdate' should replace the old macro calls with
their modern implementation.
Autoconf provides a simple means to obsolete a macro.
-- Macro: AU_DEFUN (OLD-MACRO, IMPLEMENTATION, [MESSAGE])
Define OLD-MACRO as IMPLEMENTATION. The only difference with
`AC_DEFUN' is that the user is warned that OLD-MACRO is now
obsolete.
If she then uses `autoupdate', the call to OLD-MACRO is replaced
by the modern IMPLEMENTATION. MESSAGE should include information
on what to do after running `autoupdate'; `autoupdate' prints it
as a warning, and includes it in the updated `configure.ac' file.
The details of this macro are hairy: if `autoconf' encounters an
`AU_DEFUN'ed macro, all macros inside its second argument are
expanded as usual. However, when `autoupdate' is run, only M4 and
M4sugar macros are expanded here, while all other macros are
disabled and appear literally in the updated `configure.ac'.
-- Macro: AU_ALIAS (OLD-NAME, NEW-NAME)
Used if the OLD-NAME is to be replaced by a call to NEW-MACRO with
the same parameters. This happens for example if the macro was
renamed.

File: autoconf.info, Node: Coding Style, Prev: Obsoleting Macros, Up: Writing Autoconf Macros
9.6 Coding Style
================
The Autoconf macros follow a strict coding style. You are encouraged to
follow this style, especially if you intend to distribute your macro,
either by contributing it to Autoconf itself, or via other means.
The first requirement is to pay great attention to the quotation.
For more details, see *Note Autoconf Language::, and *Note M4
Quotation::.
Do not try to invent new interfaces. It is likely that there is a
macro in Autoconf that resembles the macro you are defining: try to
stick to this existing interface (order of arguments, default values,
etc.). We _are_ conscious that some of these interfaces are not
perfect; nevertheless, when harmless, homogeneity should be preferred
over creativity.
Be careful about clashes both between M4 symbols and between shell
variables.
If you stick to the suggested M4 naming scheme (*note Macro Names::),
you are unlikely to generate conflicts. Nevertheless, when you need to
set a special value, _avoid using a regular macro name_; rather, use an
"impossible" name. For instance, up to version 2.13, the macro
`AC_SUBST' used to remember what SYMBOL macros were already defined by
setting `AC_SUBST_SYMBOL', which is a regular macro name. But since
there is a macro named `AC_SUBST_FILE', it was just impossible to
`AC_SUBST(FILE)'! In this case, `AC_SUBST(SYMBOL)' or
`_AC_SUBST(SYMBOL)' should have been used (yes, with the parentheses).
No Autoconf macro should ever enter the user-variable name space;
i.e., except for the variables that are the actual result of running the
macro, all shell variables should start with `ac_'. In addition, small
macros or any macro that is likely to be embedded in other macros
should be careful not to use obvious names.
Do not use `dnl' to introduce comments: most of the comments you are
likely to write are either header comments which are not output anyway,
or comments that should make their way into `configure'. There are
exceptional cases where you do want to comment special M4 constructs,
in which case `dnl' is right, but keep in mind that it is unlikely.
M4 ignores the leading blanks and newlines before each argument.
Use this feature to indent in such a way that arguments are (more or
less) aligned with the opening parenthesis of the macro being called.
For instance, instead of
AC_CACHE_CHECK(for EMX OS/2 environment,
ac_cv_emxos2,
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])],
[ac_cv_emxos2=yes], [ac_cv_emxos2=no])])
write
AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
[ac_cv_emxos2=yes],
[ac_cv_emxos2=no])])
or even
AC_CACHE_CHECK([for EMX OS/2 environment],
[ac_cv_emxos2],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],
[return __EMX__;])],
[ac_cv_emxos2=yes],
[ac_cv_emxos2=no])])
When using `AC_RUN_IFELSE' or any macro that cannot work when
cross-compiling, provide a pessimistic value (typically `no').
Feel free to use various tricks to prevent auxiliary tools, such as
syntax-highlighting editors, from behaving improperly. For instance,
instead of:
m4_bpatsubst([$1], [$"])
use
m4_bpatsubst([$1], [$""])
so that Emacsen do not open an endless "string" at the first quote.
For the same reasons, avoid:
test $[#] != 0
and use:
test $[@%:@] != 0
Otherwise, the closing bracket would be hidden inside a `#'-comment,
breaking the bracket-matching highlighting from Emacsen. Note the
preferred style to escape from M4: `$[1]', `$[@]', etc. Do not escape
when it is unnecessary. Common examples of useless quotation are
`[$]$1' (write `$$1'), `[$]var' (use `$var'), etc. If you add
portability issues to the picture, you'll prefer `${1+"$[@]"}' to
`"[$]@"', and you'll prefer do something better than hacking Autoconf
`:-)'.
When using `sed', don't use `-e' except for indenting purposes.
With the `s' and `y' commands, the preferred separator is `/' unless
`/' itself might appear in the pattern or replacement, in which case
you should use `|', or optionally `,' if you know the pattern and
replacement cannot contain a file name. If none of these characters
will do, choose a printable character that cannot appear in the pattern
or replacement. Characters from the set `"#$&'()*;<=>?`|~' are good
choices if the pattern or replacement might contain a file name, since
they have special meaning to the shell and are less likely to occur in
file names.
*Note Macro Definitions::, for details on how to define a macro. If
a macro doesn't use `AC_REQUIRE', is expected to never be the object of
an `AC_REQUIRE' directive, and macros required by other macros inside
arguments do not need to be expanded before this macro, then use
`m4_define'. In case of doubt, use `AC_DEFUN'. All the `AC_REQUIRE'
statements should be at the beginning of the macro, and each statement
should be followed by `dnl'.
You should not rely on the number of arguments: instead of checking
whether an argument is missing, test that it is not empty. It provides
both a simpler and a more predictable interface to the user, and saves
room for further arguments.
Unless the macro is short, try to leave the closing `])' at the
beginning of a line, followed by a comment that repeats the name of the
macro being defined. This introduces an additional newline in
`configure'; normally, that is not a problem, but if you want to remove
it you can use `[]dnl' on the last line. You can similarly use `[]dnl'
after a macro call to remove its newline. `[]dnl' is recommended
instead of `dnl' to ensure that M4 does not interpret the `dnl' as
being attached to the preceding text or macro output. For example,
instead of:
AC_DEFUN([AC_PATH_X],
[AC_MSG_CHECKING([for X])
AC_REQUIRE_CPP()
# ...omitted...
AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
fi])
you would write:
AC_DEFUN([AC_PATH_X],
[AC_REQUIRE_CPP()[]dnl
AC_MSG_CHECKING([for X])
# ...omitted...
AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
fi[]dnl
])# AC_PATH_X
If the macro is long, try to split it into logical chunks.
Typically, macros that check for a bug in a function and prepare its
`AC_LIBOBJ' replacement should have an auxiliary macro to perform this
setup. Do not hesitate to introduce auxiliary macros to factor your
code.
In order to highlight the recommended coding style, here is a macro
written the old way:
dnl Check for EMX on OS/2.
dnl _AC_EMXOS2
AC_DEFUN(_AC_EMXOS2,
[AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2,
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)],
ac_cv_emxos2=yes, ac_cv_emxos2=no)])
test "$ac_cv_emxos2" = yes && EMXOS2=yes])
and the new way:
# _AC_EMXOS2
# ----------
# Check for EMX on OS/2.
m4_define([_AC_EMXOS2],
[AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
[ac_cv_emxos2=yes],
[ac_cv_emxos2=no])])
test "$ac_cv_emxos2" = yes && EMXOS2=yes[]dnl
])# _AC_EMXOS2

File: autoconf.info, Node: Portable Shell, Next: Portable Make, Prev: Writing Autoconf Macros, Up: Top
10 Portable Shell Programming
*****************************
When writing your own checks, there are some shell-script programming
techniques you should avoid in order to make your code portable. The
Bourne shell and upward-compatible shells like the Korn shell and Bash
have evolved over the years, but to prevent trouble, do not take
advantage of features that were added after Unix version 7, circa 1977
(*note Systemology::).
You should not use shell functions, aliases, negated character
classes, or other features that are not found in all Bourne-compatible
shells; restrict yourself to the lowest common denominator. Even
`unset' is not supported by all shells!
Some ancient systems have quite small limits on the length of the
`#!' line; for instance, 32 bytes (not including the newline) on SunOS
4. A few ancient 4.2BSD based systems (such as Dynix circa 1984)
required a single space between the `#!' and the `/'. However, these
ancient systems are no longer of practical concern.
The set of external programs you should run in a `configure' script
is fairly small. *Note Utilities in Makefiles: (standards)Utilities in
Makefiles, for the list. This restriction allows users to start out
with a fairly small set of programs and build the rest, avoiding too
many interdependencies between packages.
Some of these external utilities have a portable subset of features;
see *Note Limitations of Usual Tools::.
There are other sources of documentation about shells. The
specification for the Posix Shell Command Language
(http://www.opengroup.org/susv3/utilities/xcu_chap02.html), though more
generous than the restrictive shell subset described above, is fairly
portable nowadays. Also please see the Shell FAQs
(http://www.faqs.org/faqs/unix-faq/shell/).
* Menu:
* Shellology:: A zoology of shells
* Here-Documents:: Quirks and tricks
* File Descriptors:: FDs and redirections
* File System Conventions:: File names
* Shell Substitutions:: Variable and command expansions
* Assignments:: Varying side effects of assignments
* Parentheses:: Parentheses in shell scripts
* Slashes:: Slashes in shell scripts
* Special Shell Variables:: Variables you should not change
* Limitations of Builtins:: Portable use of not so portable /bin/sh
* Limitations of Usual Tools:: Portable use of portable tools

File: autoconf.info, Node: Shellology, Next: Here-Documents, Up: Portable Shell
10.1 Shellology
===============
There are several families of shells, most prominently the Bourne family
and the C shell family which are deeply incompatible. If you want to
write portable shell scripts, avoid members of the C shell family. The
the Shell difference FAQ
(http://www.faqs.org/faqs/unix-faq/shell/shell-differences/) includes a
small history of Posix shells, and a comparison between several of them.
Below we describe some of the members of the Bourne shell family.
Ash
Ash is often used on GNU/Linux and BSD systems as a light-weight
Bourne-compatible shell. Ash 0.2 has some bugs that are fixed in
the 0.3.x series, but portable shell scripts should work around
them, since version 0.2 is still shipped with many GNU/Linux
distributions.
To be compatible with Ash 0.2:
- don't use `$?' after expanding empty or unset variables, or
at the start of an `eval':
foo=
false
$foo
echo "Do not use it: $?"
false
eval 'echo "Do not use it: $?"'
- don't use command substitution within variable expansion:
cat ${FOO=`bar`}
- beware that single builtin substitutions are not performed by
a subshell, hence their effect applies to the current shell!
*Note Shell Substitutions::, item "Command Substitution".
Bash
To detect whether you are running Bash, test whether
`BASH_VERSION' is set. To require Posix compatibility, run `set
-o posix'. *Note Bash Posix Mode: (bash)Bash POSIX Mode, for
details.
Bash 2.05 and later
Versions 2.05 and later of Bash use a different format for the
output of the `set' builtin, designed to make evaluating its
output easier. However, this output is not compatible with earlier
versions of Bash (or with many other shells, probably). So if you
use Bash 2.05 or higher to execute `configure', you'll need to use
Bash 2.05 for all other build tasks as well.
Ksh
The Korn shell is compatible with the Bourne family and it mostly
conforms to Posix. It has two major variants commonly called
`ksh88' and `ksh93', named after the years of initial release. It
is usually called `ksh', but is called `sh' on some hosts if you
set your path appropriately.
Solaris systems have three variants: `/usr/bin/ksh' is `ksh88'; it
is standard on Solaris 2.0 and later. `/usr/xpg4/bin/sh' is a
Posix-compliant variant of `ksh88'; it is standard on Solaris 9
and later. `/usr/dt/bin/dtksh' is `ksh93'. Variants that are not
standard may be parts of optional packages. There is no extra
charge for these packages, but they are not part of a minimal OS
install and therefore some installations may not have it.
Starting with Tru64 Version 4.0, the Korn shell `/usr/bin/ksh' is
also available as `/usr/bin/posix/sh'. If the environment
variable `BIN_SH' is set to `xpg4', subsidiary invocations of the
standard shell conform to Posix.
Pdksh
A public-domain clone of the Korn shell called `pdksh' is widely
available: it has most of the `ksh88' features along with a few of
its own. It usually sets `KSH_VERSION', except if invoked as
`/bin/sh' on OpenBSD, and similarly to Bash you can require Posix
compatibility by running `set -o posix'. Unfortunately, with
`pdksh' 5.2.14 (the latest stable version as of February 2006)
Posix mode is buggy and causes `pdksh' to depart from Posix in at
least one respect:
$ echo "`echo \"hello\"`"
hello
$ set -o posix
$ echo "`echo \"hello\"`"
"hello"
The last line of output contains spurious quotes. This is yet
another reason why portable shell code should not contain
`"`...\"...\"...`"' constructs (*note Shell Substitutions::).
Zsh
To detect whether you are running `zsh', test whether
`ZSH_VERSION' is set. By default `zsh' is _not_ compatible with
the Bourne shell: you must execute `emulate sh', and for `zsh'
versions before 3.1.6-dev-18 you must also set `NULLCMD' to `:'.
*Note Compatibility: (zsh)Compatibility, for details.
The default Mac OS X `sh' was originally Zsh; it was changed to
Bash in Mac OS X 10.2.
The following discussion between Russ Allbery and Robert Lipe is
worth reading:
Russ Allbery:
The GNU assumption that `/bin/sh' is the one and only shell leads
to a permanent deadlock. Vendors don't want to break users'
existing shell scripts, and there are some corner cases in the
Bourne shell that are not completely compatible with a Posix
shell. Thus, vendors who have taken this route will _never_
(OK..."never say never") replace the Bourne shell (as `/bin/sh')
with a Posix shell.
Robert Lipe:
This is exactly the problem. While most (at least most System
V's) do have a Bourne shell that accepts shell functions most
vendor `/bin/sh' programs are not the Posix shell.
So while most modern systems do have a shell _somewhere_ that
meets the Posix standard, the challenge is to find it.

File: autoconf.info, Node: Here-Documents, Next: File Descriptors, Prev: Shellology, Up: Portable Shell
10.2 Here-Documents
===================
Don't rely on `\' being preserved just because it has no special
meaning together with the next symbol. In the native `sh' on OpenBSD
2.7 `\"' expands to `"' in here-documents with unquoted delimiter. As
a general rule, if `\\' expands to `\' use `\\' to get `\'.
With OpenBSD 2.7's `sh'
$ cat <<EOF
> \" \\
> EOF
" \
and with Bash:
bash-2.04$ cat <<EOF
> \" \\
> EOF
\" \
Some shells mishandle large here-documents: for example, Solaris 10
`dtksh' and the UnixWare 7.1.1 Posix shell, which are derived from Korn
shell version M-12/28/93d, mishandle braced variable expansion that
crosses a 1024- or 4096-byte buffer boundary within a here-document.
Only the part of the variable name after the boundary is used. For
example, `${variable}' could be replaced by the expansion of `${ble}'.
If the end of the variable name is aligned with the block boundary, the
shell reports an error, as if you used `${}'. Instead of
`${variable-default}', the shell may expand `${riable-default}', or
even `${fault}'. This bug can often be worked around by omitting the
braces: `$variable'. The bug was fixed in `ksh93g' (1998-04-30) but as
of 2006 many operating systems were still shipping older versions with
the bug.
Many older shells (including the Bourne shell) implement
here-documents inefficiently. In particular, some shells can be
extremely inefficient when a single statement contains many
here-documents. For instance if your `configure.ac' includes something
like:
if <cross_compiling>; then
assume this and that
else
check this
check that
check something else
...
on and on forever
...
fi
A shell parses the whole `if'/`fi' construct, creating temporary
files for each here-document in it. Some shells create links for such
here-documents on every `fork', so that the clean-up code they had
installed correctly removes them. It is creating the links that can
take the shell forever.
Moving the tests out of the `if'/`fi', or creating multiple
`if'/`fi' constructs, would improve the performance significantly.
Anyway, this kind of construct is not exactly the typical use of
Autoconf. In fact, it's even not recommended, because M4 macros can't
look into shell conditionals, so we may fail to expand a macro when it
was expanded before in a conditional path, and the condition turned out
to be false at runtime, and we end up not executing the macro at all.

File: autoconf.info, Node: File Descriptors, Next: File System Conventions, Prev: Here-Documents, Up: Portable Shell
10.3 File Descriptors
=====================
Most shells, if not all (including Bash, Zsh, Ash), output traces on
stderr, even for subshells. This might result in undesirable content
if you meant to capture the standard-error output of the inner command:
$ ash -x -c '(eval "echo foo >&2") 2>stderr'
$ cat stderr
+ eval echo foo >&2
+ echo foo
foo
$ bash -x -c '(eval "echo foo >&2") 2>stderr'
$ cat stderr
+ eval 'echo foo >&2'
++ echo foo
foo
$ zsh -x -c '(eval "echo foo >&2") 2>stderr'
# Traces on startup files deleted here.
$ cat stderr
+zsh:1> eval echo foo >&2
+zsh:1> echo foo
foo
One workaround is to grep out uninteresting lines, hoping not to remove
good ones.
If you intend to redirect both standard error and standard output,
redirect standard output first. This works better with HP-UX, since
its shell mishandles tracing if standard error is redirected first:
$ sh -x -c ': 2>err >out'
+ :
+ 2> err $ cat err
1> out
Don't try to redirect the standard error of a command substitution.
It must be done _inside_ the command substitution. When running `: `cd
/zorglub` 2>/dev/null' expect the error message to escape, while `: `cd
/zorglub 2>/dev/null`' works properly.
It is worth noting that Zsh (but not Ash nor Bash) makes it possible
in assignments though: `foo=`cd /zorglub` 2>/dev/null'.
Don't redirect the same file descriptor several times, as you are
doomed to failure under Ultrix.
ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995
UWS V4.4 (Rev. 11)
$ eval 'echo matter >fullness' >void
illegal io
$ eval '(echo matter >fullness)' >void
illegal io
$ (eval '(echo matter >fullness)') >void
Ambiguous output redirect.
In each case the expected result is of course `fullness' containing
`matter' and `void' being empty.
Don't rely on file descriptors 0, 1, and 2 remaining closed in a
subsidiary program. If any of these descriptors is closed, the
operating system may open an unspecified file for the descriptor in the
new process image. Posix says this may be done only if the subsidiary
program is set-user-ID or set-group-ID, but HP-UX 11.23 does it even for
ordinary programs.
Don't rely on open file descriptors being open in child processes.
In `ksh', file descriptors above 2 which are opened using `exec N>file'
are closed by a subsequent `exec' (such as that involved in the
fork-and-exec which runs a program or script). Thus, using `sh', we
have:
$ cat ./descrips
#!/bin/sh -
echo hello >&5
$ exec 5>t
$ ./descrips
$ cat t
$
hello
But using ksh:
$ exec 5>t
$ ./descrips
hello
$ cat t
$
Within the process which runs the `descrips' script, file descriptor 5
is closed.
DOS variants cannot rename or remove open files, such as in `mv foo
bar >foo' or `rm foo >foo', even though this is perfectly portable
among Posix hosts.
A few ancient systems reserved some file descriptors. By convention,
file descriptor 3 was opened to `/dev/tty' when you logged into Eighth
Edition (1985) through Tenth Edition Unix (1989). File descriptor 4
had a special use on the Stardent/Kubota Titan (circa 1990), though we
don't now remember what it was. Both these systems are obsolete, so
it's now safe to treat file descriptors 3 and 4 like any other file
descriptors.

File: autoconf.info, Node: File System Conventions, Next: Shell Substitutions, Prev: File Descriptors, Up: Portable Shell
10.4 File System Conventions
============================
Autoconf uses shell-script processing extensively, so the file names
that it processes should not contain characters that are special to the
shell. Special characters include space, tab, newline, NUL, and the
following:
" # $ & ' ( ) * ; < = > ? [ \ ` |
Also, file names should not begin with `~' or `-', and should
contain neither `-' immediately after `/' nor `~' immediately after
`:'. On Posix-like platforms, directory names should not contain `:',
as this runs afoul of `:' used as the path separator.
These restrictions apply not only to the files that you distribute,
but also to the absolute file names of your source, build, and
destination directories.
On some Posix-like platforms, `!' and `^' are special too, so they
should be avoided.
Posix lets implementations treat leading `//' specially, but
requires leading `///' and beyond to be equivalent to `/'. Most Unix
variants treat `//' like `/'. However, some treat `//' as a
"super-root" that can provide access to files that are not otherwise
reachable from `/'. The super-root tradition began with Apollo
Domain/OS, which died out long ago, but unfortunately Cygwin has
revived it.
While `autoconf' and friends are usually run on some Posix variety,
they can be used on other systems, most notably DOS variants. This
impacts several assumptions regarding file names.
For example, the following code:
case $foo_dir in
/*) # Absolute
;;
*)
foo_dir=$dots$foo_dir ;;
esac
fails to properly detect absolute file names on those systems, because
they can use a drivespec, and usually use a backslash as directory
separator. If you want to be portable to DOS variants (at the price of
rejecting valid but oddball Posix file names like `a:\b'), you can
check for absolute file names like this:
case $foo_dir in
[\\/]* | ?:[\\/]* ) # Absolute
;;
*)
foo_dir=$dots$foo_dir ;;
esac
Make sure you quote the brackets if appropriate and keep the backslash
as first character (*note Limitations of Builtins::).
Also, because the colon is used as part of a drivespec, these
systems don't use it as path separator. When creating or accessing
paths, you can use the `PATH_SEPARATOR' output variable instead.
`configure' sets this to the appropriate value (`:' or `;') when it
starts up.
File names need extra care as well. While DOS variants that are
Posixy enough to run `autoconf' (such as DJGPP) are usually able to
handle long file names properly, there are still limitations that can
seriously break packages. Several of these issues can be easily
detected by the doschk
(ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz) package.
A short overview follows; problems are marked with SFN/LFN to
indicate where they apply: SFN means the issues are only relevant to
plain DOS, not to DOS under Microsoft Windows variants, while LFN
identifies problems that exist even under Microsoft Windows variants.
No multiple dots (SFN)
DOS cannot handle multiple dots in file names. This is an
especially important thing to remember when building a portable
configure script, as `autoconf' uses a .in suffix for template
files.
This is perfectly OK on Posix variants:
AC_CONFIG_HEADERS([config.h])
AC_CONFIG_FILES([source.c foo.bar])
AC_OUTPUT
but it causes problems on DOS, as it requires `config.h.in',
`source.c.in' and `foo.bar.in'. To make your package more portable
to DOS-based environments, you should use this instead:
AC_CONFIG_HEADERS([config.h:config.hin])
AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in])
AC_OUTPUT
No leading dot (SFN)
DOS cannot handle file names that start with a dot. This is
usually not important for `autoconf'.
Case insensitivity (LFN)
DOS is case insensitive, so you cannot, for example, have both a
file called `INSTALL' and a directory called `install'. This also
affects `make'; if there's a file called `INSTALL' in the
directory, `make install' does nothing (unless the `install'
target is marked as PHONY).
The 8+3 limit (SFN)
Because the DOS file system only stores the first 8 characters of
the file name and the first 3 of the extension, those must be
unique. That means that `foobar-part1.c', `foobar-part2.c' and
`foobar-prettybird.c' all resolve to the same file name
(`FOOBAR-P.C'). The same goes for `foo.bar' and `foo.bartender'.
The 8+3 limit is not usually a problem under Microsoft Windows, as
it uses numeric tails in the short version of file names to make
them unique. However, a registry setting can turn this behavior
off. While this makes it possible to share file trees containing
long file names between SFN and LFN environments, it also means
the above problem applies there as well.
Invalid characters (LFN)
Some characters are invalid in DOS file names, and should therefore
be avoided. In a LFN environment, these are `/', `\', `?', `*',
`:', `<', `>', `|' and `"'. In a SFN environment, other
characters are also invalid. These include `+', `,', `[' and `]'.
Invalid names (LFN)
Some DOS file names are reserved, and cause problems if you try to
use files with those names. These names include `CON', `AUX',
`COM1', `COM2', `COM3', `COM4', `LPT1', `LPT2', `LPT3', `NUL', and
`PRN'. File names are case insensitive, so even names like
`aux/config.guess' are disallowed.

File: autoconf.info, Node: Shell Substitutions, Next: Assignments, Prev: File System Conventions, Up: Portable Shell
10.5 Shell Substitutions
========================
Contrary to a persistent urban legend, the Bourne shell does not
systematically split variables and back-quoted expressions, in
particular on the right-hand side of assignments and in the argument of
`case'. For instance, the following code:
case "$given_srcdir" in
.) top_srcdir="`echo "$dots" | sed 's,/$,,'`" ;;
*) top_srcdir="$dots$given_srcdir" ;;
esac
is more readable when written as:
case $given_srcdir in
.) top_srcdir=`echo "$dots" | sed 's,/$,,'` ;;
*) top_srcdir=$dots$given_srcdir ;;
esac
and in fact it is even _more_ portable: in the first case of the first
attempt, the computation of `top_srcdir' is not portable, since not all
shells properly understand `"`..."..."...`"'. Worse yet, not all
shells understand `"`...\"...\"...`"' the same way. There is just no
portable way to use double-quoted strings inside double-quoted
back-quoted expressions (pfew!).
`$@'
One of the most famous shell-portability issues is related to
`"$@"'. When there are no positional arguments, Posix says that
`"$@"' is supposed to be equivalent to nothing, but the original
Unix version 7 Bourne shell treated it as equivalent to `""'
instead, and this behavior survives in later implementations like
Digital Unix 5.0.
The traditional way to work around this portability problem is to
use `${1+"$@"}'. Unfortunately this method does not work with Zsh
(3.x and 4.x), which is used on Mac OS X. When emulating the
Bourne shell, Zsh performs word splitting on `${1+"$@"}':
zsh $ emulate sh
zsh $ for i in "$@"; do echo $i; done
Hello World
!
zsh $ for i in ${1+"$@"}; do echo $i; done
Hello
World
!
Zsh handles plain `"$@"' properly, but we can't use plain `"$@"'
because of the portability problems mentioned above. One
workaround relies on Zsh's "global aliases" to convert `${1+"$@"}'
into `"$@"' by itself:
test "${ZSH_VERSION+set}" = set && alias -g '${1+"$@"}'='"$@"'
A more conservative workaround is to avoid `"$@"' if it is
possible that there may be no positional arguments. For example,
instead of:
cat conftest.c "$@"
you can use this instead:
case $# in
0) cat conftest.c;;
*) cat conftest.c "$@";;
esac
Autoconf macros often use the `set' command to update `$@', so if
you are writing shell code intended for `configure' you should not
assume that the value of `$@' persists for any length of time.
`${10}'
The 10th, 11th, ... positional parameters can be accessed only
after a `shift'. The 7th Edition shell reported an error if given
`${10}', and Solaris 10 `/bin/sh' still acts that way:
$ set 1 2 3 4 5 6 7 8 9 10
$ echo ${10}
bad substitution
`${VAR:-VALUE}'
Old BSD shells, including the Ultrix `sh', don't accept the colon
for any shell substitution, and complain and die.
`${VAR=LITERAL}'
Be sure to quote:
: ${var='Some words'}
otherwise some shells, such as on Digital Unix V 5.0, die because
of a "bad substitution".
Solaris `/bin/sh' has a frightening bug in its interpretation of
this. Imagine you need set a variable to a string containing `}'.
This `}' character confuses Solaris `/bin/sh' when the affected
variable was already set. This bug can be exercised by running:
$ unset foo
$ foo=${foo='}'}
$ echo $foo
}
$ foo=${foo='}' # no error; this hints to what the bug is
$ echo $foo
}
$ foo=${foo='}'}
$ echo $foo
}}
^ ugh!
It seems that `}' is interpreted as matching `${', even though it
is enclosed in single quotes. The problem doesn't happen using
double quotes.
`${VAR=EXPANDED-VALUE}'
On Ultrix, running
default="yu,yaa"
: ${var="$default"}
sets VAR to `M-yM-uM-,M-yM-aM-a', i.e., the 8th bit of each char
is set. You don't observe the phenomenon using a simple `echo
$var' since apparently the shell resets the 8th bit when it
expands $var. Here are two means to make this shell confess its
sins:
$ cat -v <<EOF
$var
EOF
and
$ set | grep '^var=' | cat -v
One classic incarnation of this bug is:
default="a b c"
: ${list="$default"}
for c in $list; do
echo $c
done
You'll get `a b c' on a single line. Why? Because there are no
spaces in `$list': there are `M- ', i.e., spaces with the 8th bit
set, hence no IFS splitting is performed!!!
One piece of good news is that Ultrix works fine with `:
${list=$default}'; i.e., if you _don't_ quote. The bad news is
then that QNX 4.25 then sets LIST to the _last_ item of DEFAULT!
The portable way out consists in using a double assignment, to
switch the 8th bit twice on Ultrix:
list=${list="$default"}
...but beware of the `}' bug from Solaris (see above). For safety,
use:
test "${var+set}" = set || var={VALUE}
``COMMANDS`'
Posix requires shells to trim all trailing newlines from command
output before substituting it, so assignments like `dir=`echo
"$file" | tr a A`' do not work as expected if `$file' ends in a
newline.
While in general it makes no sense, do not substitute a single
builtin with side effects, because Ash 0.2, trying to optimize,
does not fork a subshell to perform the command.
For instance, if you wanted to check that `cd' is silent, do not
use `test -z "`cd /`"' because the following can happen:
$ pwd
/tmp
$ test -z "`cd /`" && pwd
/
The result of `foo=`exit 1`' is left as an exercise to the reader.
The MSYS shell leaves a stray byte in the expansion of a
double-quoted command substitution of a native program, if the end
of the substution is not aligned with the end of the double quote.
This may be worked around by inserting another pair of quotes:
$ echo "`printf 'foo\r\n'` bar" > broken
$ echo "`printf 'foo\r\n'`"" bar" | cmp - broken
- broken differ: char 4, line 1
`$(COMMANDS)'
This construct is meant to replace ``COMMANDS`', and it has most
of the problems listed under ``COMMANDS`'.
This construct can be nested while this is impossible to do
portably with back quotes. Unfortunately it is not yet
universally supported. Most notably, even recent releases of
Solaris don't support it:
$ showrev -c /bin/sh | grep version
Command version: SunOS 5.10 Generic 121004-01 Oct 2005
$ echo $(echo blah)
syntax error: `(' unexpected
nor does IRIX 6.5's Bourne shell:
$ uname -a
IRIX firebird-image 6.5 07151432 IP22
$ echo $(echo blah)
$(echo blah)
If you do use `$(COMMANDS)', make sure that the commands do not
start with a parenthesis, as that would cause confusion with a
different notation `$((EXPRESSION))' that in modern shells is an
arithmetic expression not a command. To avoid the confusion,
insert a space between the two opening parentheses.
Avoid COMMANDS that contain unbalanced parentheses in
here-documents, comments, or case statement patterns, as many
shells mishandle them. For example, Bash 3.1, `ksh88', `pdksh'
5.2.14, and Zsh 4.2.6 all mishandle the following valid command:
echo $(case x in x) echo hello;; esac)
`^'
Always quote `^', otherwise traditional shells such as `/bin/sh'
on Solaris 10 treat this like `|'.

File: autoconf.info, Node: Assignments, Next: Parentheses, Prev: Shell Substitutions, Up: Portable Shell
10.6 Assignments
================
When setting several variables in a row, be aware that the order of the
evaluation is undefined. For instance `foo=1 foo=2; echo $foo' gives
`1' with Solaris `/bin/sh', but `2' with Bash. You must use `;' to
enforce the order: `foo=1; foo=2; echo $foo'.
Don't rely on the following to find `subdir/program':
PATH=subdir$PATH_SEPARATOR$PATH program
as this does not work with Zsh 3.0.6. Use something like this instead:
(PATH=subdir$PATH_SEPARATOR$PATH; export PATH; exec program)
Don't rely on the exit status of an assignment: Ash 0.2 does not
change the status and propagates that of the last statement:
$ false || foo=bar; echo $?
1
$ false || foo=`:`; echo $?
0
and to make things even worse, QNX 4.25 just sets the exit status to 0
in any case:
$ foo=`exit 1`; echo $?
0
To assign default values, follow this algorithm:
1. If the default value is a literal and does not contain any closing
brace, use:
: ${var='my literal'}
2. If the default value contains no closing brace, has to be
expanded, and the variable being initialized is not intended to be
IFS-split (i.e., it's not a list), then use:
: ${var="$default"}
3. If the default value contains no closing brace, has to be
expanded, and the variable being initialized is intended to be
IFS-split (i.e., it's a list), then use:
var=${var="$default"}
4. If the default value contains a closing brace, then use:
test "${var+set}" = set || var="has a '}'"
In most cases `var=${var="$default"}' is fine, but in case of doubt,
just use the last form. *Note Shell Substitutions::, items
`${VAR:-VALUE}' and `${VAR=VALUE}' for the rationale.

File: autoconf.info, Node: Parentheses, Next: Slashes, Prev: Assignments, Up: Portable Shell
10.7 Parentheses in Shell Scripts
=================================
Beware of two opening parentheses in a row, as some shell
implementations mishandle them. For example, `pdksh' 5.2.14 misparses
the following code:
if ((true) || false); then
echo ok
fi
To work around this problem, insert a space between the two opening
parentheses. There is a similar problem and workaround with `$(('; see
*Note Shell Substitutions::.
Posix requires support for `case' patterns with opening parentheses
like this:
case $file_name in
(*.c) echo "C source code";;
esac
but the `(' in this example is not portable to many older Bourne shell
implementations. It can be omitted safely.

File: autoconf.info, Node: Slashes, Next: Special Shell Variables, Prev: Parentheses, Up: Portable Shell
10.8 Slashes in Shell Scripts
=============================
Unpatched Tru64 5.1 `sh' omits the last slash of command-line arguments
that contain two trailing slashes:
$ echo / // /// //// .// //.
/ / // /// ./ //.
$ x=//
$ eval "echo \$x"
/
$ set -x
$ echo abc | tr -t ab //
+ echo abc
+ tr -t ab /
/bc
Unpatched Tru64 4.0 `sh' adds a slash after `"$var"' if the variable
is empty and the second double-quote is followed by a word that begins
and ends with slash:
$ sh -xc 'p=; echo "$p"/ouch/'
p=
+ echo //ouch/
//ouch/
However, our understanding is that patches are available, so perhaps
it's not worth worrying about working around these horrendous bugs.

File: autoconf.info, Node: Special Shell Variables, Next: Limitations of Builtins, Prev: Slashes, Up: Portable Shell
10.9 Special Shell Variables
============================
Some shell variables should not be used, since they can have a deep
influence on the behavior of the shell. In order to recover a sane
behavior from the shell, some variables should be unset, but `unset' is
not portable (*note Limitations of Builtins::) and a fallback value is
needed.
As a general rule, shell variable names containing a lower-case
letter are safe; you can define and use these variables without
worrying about their effect on the underlying system, and without
worrying about whether the shell changes them unexpectedly. (The
exception is the shell variable `status', as described below.)
Here is a list of names that are known to cause trouble. This list
is not exhaustive, but you should be safe if you avoid the name
`status' and names containing only upper-case letters and underscores.
`_'
Many shells reserve `$_' for various purposes, e.g., the name of
the last command executed.
`BIN_SH'
In Tru64, if `BIN_SH' is set to `xpg4', subsidiary invocations of
the standard shell conform to Posix.
`CDPATH'
When this variable is set it specifies a list of directories to
search when invoking `cd' with a relative file name that did not
start with `./' or `../'. Posix 1003.1-2001 says that if a
nonempty directory name from `CDPATH' is used successfully, `cd'
prints the resulting absolute file name. Unfortunately this
output can break idioms like `abs=`cd src && pwd`' because `abs'
receives the name twice. Also, many shells do not conform to this
part of Posix; for example, `zsh' prints the result only if a
directory name other than `.' was chosen from `CDPATH'.
In practice the shells that have this problem also support
`unset', so you can work around the problem as follows:
(unset CDPATH) >/dev/null 2>&1 && unset CDPATH
You can also avoid output by ensuring that your directory name is
absolute or anchored at `./', as in `abs=`cd ./src && pwd`'.
Autoconf-generated scripts automatically unset `CDPATH' if
possible, so you need not worry about this problem in those
scripts.
`DUALCASE'
In the MKS shell, case statements and file name generation are
case-insensitive unless `DUALCASE' is nonzero. Autoconf-generated
scripts export this variable when they start up.
`ENV'
`MAIL'
`MAILPATH'
`PS1'
`PS2'
`PS4'
These variables should not matter for shell scripts, since they are
supposed to affect only interactive shells. However, at least one
shell (the pre-3.0 UWIN Korn shell) gets confused about whether it
is interactive, which means that (for example) a `PS1' with a side
effect can unexpectedly modify `$?'. To work around this bug,
Autoconf-generated scripts do something like this:
(unset ENV) >/dev/null 2>&1 && unset ENV MAIL MAILPATH
PS1='$ '
PS2='> '
PS4='+ '
`IFS'
Long ago, shell scripts inherited `IFS' from the environment, but
this caused many problems so modern shells ignore any environment
settings for `IFS'.
Don't set the first character of `IFS' to backslash. Indeed,
Bourne shells use the first character (backslash) when joining the
components in `"$@"' and some shells then reinterpret (!) the
backslash escapes, so you can end up with backspace and other
strange characters.
The proper value for `IFS' (in regular code, not when performing
splits) is `<SPC><TAB><RET>'. The first character is especially
important, as it is used to join the arguments in `$*'; however,
note that traditional shells, but also bash-2.04, fail to adhere
to this and join with a space anyway.
`LANG'
`LC_ALL'
`LC_COLLATE'
`LC_CTYPE'
`LC_MESSAGES'
`LC_MONETARY'
`LC_NUMERIC'
`LC_TIME'
Autoconf-generated scripts normally set all these variables to `C'
because so much configuration code assumes the C locale and Posix
requires that locale environment variables be set to `C' if the C
locale is desired. However, some older, nonstandard systems
(notably SCO) break if locale environment variables are set to
`C', so when running on these systems Autoconf-generated scripts
unset the variables instead.
`LANGUAGE'
`LANGUAGE' is not specified by Posix, but it is a GNU extension
that overrides `LC_ALL' in some cases, so Autoconf-generated
scripts set it too.
`LC_ADDRESS'
`LC_IDENTIFICATION'
`LC_MEASUREMENT'
`LC_NAME'
`LC_PAPER'
`LC_TELEPHONE'
These locale environment variables are GNU extensions. They are
treated like their Posix brethren (`LC_COLLATE', etc.) as
described above.
`LINENO'
Most modern shells provide the current line number in `LINENO'.
Its value is the line number of the beginning of the current
command. Autoconf attempts to execute `configure' with a shell
that supports `LINENO'. If no such shell is available, it
attempts to implement `LINENO' with a Sed prepass that replaces
each instance of the string `$LINENO' (not followed by an
alphanumeric character) with the line's number.
You should not rely on `LINENO' within `eval', as the behavior
differs in practice. Also, the possibility of the Sed prepass
means that you should not rely on `$LINENO' when quoted, when in
here-documents, or when in long commands that cross line
boundaries. Subshells should be OK, though. In the following
example, lines 1, 6, and 9 are portable, but the other instances of
`LINENO' are not:
$ cat lineno
echo 1. $LINENO
cat <<EOF
3. $LINENO
4. $LINENO
EOF
( echo 6. $LINENO )
eval 'echo 7. $LINENO'
echo 8. '$LINENO'
echo 9. $LINENO '
10.' $LINENO
$ bash-2.05 lineno
1. 1
3. 2
4. 2
6. 6
7. 1
8. $LINENO
9. 9
10. 9
$ zsh-3.0.6 lineno
1. 1
3. 2
4. 2
6. 6
7. 7
8. $LINENO
9. 9
10. 9
$ pdksh-5.2.14 lineno
1. 1
3. 2
4. 2
6. 6
7. 0
8. $LINENO
9. 9
10. 9
$ sed '=' <lineno |
> sed '
> N
> s,$,-,
> t loop
> :loop
> s,^\([0-9]*\)\(.*\)[$]LINENO\([^a-zA-Z0-9_]\),\1\2\1\3,
> t loop
> s,-$,,
> s,^[0-9]*\n,,
> ' |
> sh
1. 1
3. 3
4. 4
6. 6
7. 7
8. 8
9. 9
10. 10
`NULLCMD'
When executing the command `>foo', `zsh' executes `$NULLCMD >foo'
unless it is operating in Bourne shell compatibility mode and the
`zsh' version is newer than 3.1.6-dev-18. If you are using an
older `zsh' and forget to set `NULLCMD', your script might be
suspended waiting for data on its standard input.
`PATH_SEPARATOR'
On DJGPP systems, the `PATH_SEPARATOR' environment variable can be
set to either `:' or `;' to control the path separator Bash uses
to set up certain environment variables (such as `PATH'). You can
set this variable to `;' if you want `configure' to use `;' as a
separator; this might be useful if you plan to use non-Posix
shells to execute files. *Note File System Conventions::, for
more information about `PATH_SEPARATOR'.
`PWD'
Posix 1003.1-2001 requires that `cd' and `pwd' must update the
`PWD' environment variable to point to the logical name of the
current directory, but traditional shells do not support this.
This can cause confusion if one shell instance maintains `PWD' but
a subsidiary and different shell does not know about `PWD' and
executes `cd'; in this case `PWD' points to the wrong directory.
Use ``pwd`' rather than `$PWD'.
`RANDOM'
Many shells provide `RANDOM', a variable that returns a different
integer each time it is used. Most of the time, its value does not
change when it is not used, but on IRIX 6.5 the value changes all
the time. This can be observed by using `set'. It is common
practice to use `$RANDOM' as part of a file name, but code
shouldn't rely on `$RANDOM' expanding to a nonempty string.
`status'
This variable is an alias to `$?' for `zsh' (at least 3.1.6),
hence read-only. Do not use it.

File: autoconf.info, Node: Limitations of Builtins, Next: Limitations of Usual Tools, Prev: Special Shell Variables, Up: Portable Shell
10.10 Limitations of Shell Builtins
===================================
No, no, we are serious: some shells do have limitations! :)
You should always keep in mind that any builtin or command may
support options, and therefore differ in behavior with arguments
starting with a dash. For instance, the innocent `echo "$word"' can
give unexpected results when `word' starts with a dash. It is often
possible to avoid this problem using `echo "x$word"', taking the `x'
into account later in the pipe.
`.'
Use `.' only with regular files (use `test -f'). Bash 2.03, for
instance, chokes on `. /dev/null'. Also, remember that `.' uses
`PATH' if its argument contains no slashes, so if you want to use
`.' on a file `foo' in the current directory, you must use `.
./foo'.
`!'
The Unix version 7 shell did not support negating the exit status
of commands with `!', and this feature is still absent from some
shells (e.g., Solaris `/bin/sh'). Shell code like this:
if ! cmp file1 file2 >/dev/null 2>&1; then
echo files differ or trouble
fi
is therefore not portable in practice. Typically it is easy to
rewrite such code, e.g.:
cmp file1 file2 >/dev/null 2>&1 ||
echo files differ or trouble
More generally, one can always rewrite `! COMMAND' as:
if COMMAND; then (exit 1); else :; fi
`break'
The use of `break 2' etc. is safe.
`case'
You don't need to quote the argument; no splitting is performed.
You don't need the final `;;', but you should use it.
Because of a bug in its `fnmatch', Bash fails to properly handle
backslashes in character classes:
bash-2.02$ case /tmp in [/\\]*) echo OK;; esac
bash-2.02$
This is extremely unfortunate, since you are likely to use this
code to handle Posix or MS-DOS absolute file names. To work
around this bug, always put the backslash first:
bash-2.02$ case '\TMP' in [\\/]*) echo OK;; esac
OK
bash-2.02$ case /tmp in [\\/]*) echo OK;; esac
OK
Many Bourne shells cannot handle closing brackets in character
classes correctly.
Some shells also have problems with backslash escaping in case you
do not want to match the backslash: both a backslash and the
escaped character match this pattern. To work around this,
specify the character class in a variable, so that quote removal
does not apply afterwards, and the special characters don't have
to be backslash-escaped:
$ case '\' in [\<]) echo OK;; esac
OK
$ scanset='[<]'; case '\' in $scanset) echo OK;; esac
$
Even with this, Solaris `ksh' matches a backslash if the set
contains any of the characters `|', `&', `(', or `)'.
Conversely, Tru64 `ksh' (circa 2003) erroneously always matches a
closing parenthesis if not specified in a character class:
$ case foo in *\)*) echo fail ;; esac
fail
$ case foo in *')'*) echo fail ;; esac
fail
Some shells, such as Ash 0.3.8, are confused by an empty
`case'/`esac':
ash-0.3.8 $ case foo in esac;
error-->Syntax error: ";" unexpected (expecting ")")
Many shells still do not support parenthesized cases, which is a
pity for those of us using tools that rely on balanced
parentheses. For instance, Solaris `/bin/sh':
$ case foo in (foo) echo foo;; esac
error-->syntax error: `(' unexpected
`cd'
Posix 1003.1-2001 requires that `cd' must support the `-L'
("logical") and `-P' ("physical") options, with `-L' being the
default. However, traditional shells do not support these
options, and their `cd' command has the `-P' behavior.
Portable scripts should assume neither option is supported, and
should assume neither behavior is the default. This can be a bit
tricky, since the Posix default behavior means that, for example,
`ls ..' and `cd ..' may refer to different directories if the
current logical directory is a symbolic link. It is safe to use
`cd DIR' if DIR contains no `..' components. Also,
Autoconf-generated scripts check for this problem when computing
variables like `ac_top_srcdir' (*note Configuration Actions::), so
it is safe to `cd' to these variables.
See *Note Special Shell Variables::, for portability problems
involving `cd' and the `CDPATH' environment variable. Also please
see the discussion of the `pwd' command.
`echo'
The simple `echo' is probably the most surprising source of
portability troubles. It is not possible to use `echo' portably
unless both options and escape sequences are omitted. New
applications which are not aiming at portability should use
`printf' instead of `echo'.
Don't expect any option. *Note Preset Output Variables::, `ECHO_N'
etc. for a means to simulate `-n'.
Do not use backslashes in the arguments, as there is no consensus
on their handling. For `echo '\n' | wc -l', the `sh' of Solaris
outputs 2, but Bash and Zsh (in `sh' emulation mode) output 1.
The problem is truly `echo': all the shells understand `'\n'' as
the string composed of a backslash and an `n'.
Because of these problems, do not pass a string containing
arbitrary characters to `echo'. For example, `echo "$foo"' is safe
if you know that FOO's value cannot contain backslashes and cannot
start with `-', but otherwise you should use a here-document like
this:
cat <<EOF
$foo
EOF
`eval'
The `eval' command is useful in limited circumstances, e.g., using
commands like `eval table_$key=\$value' and `eval
value=table_$key' to simulate a hash table when the key is known
to be alphanumeric. However, `eval' is tricky to use on arbitrary
arguments, even when it is implemented correctly.
It is obviously unwise to use `eval $cmd' if the string value of
`cmd' was derived from an untrustworthy source. But even if the
string value is valid, `eval $cmd' might not work as intended,
since it causes field splitting and file name expansion to occur
twice, once for the `eval' and once for the command itself. It is
therefore safer to use `eval "$cmd"'. For example, if CMD has the
value `cat test?.c', `eval $cmd' might expand to the equivalent of
`cat test;.c' if there happens to be a file named `test;.c' in the
current directory; and this in turn mistakenly attempts to invoke
`cat' on the file `test' and then execute the command `.c'. To
avoid this problem, use `eval "$cmd"' rather than `eval $cmd'.
However, suppose that you want to output the text of the evaluated
command just before executing it. Assuming the previous example,
`echo "Executing: $cmd"' outputs `Executing: cat test?.c', but
this output doesn't show the user that `test;.c' is the actual name
of the copied file. Conversely, `eval "echo Executing: $cmd"'
works on this example, but it fails with `cmd='cat foo >bar'',
since it mistakenly replaces the contents of `bar' by the string
`cat foo'. No simple, general, and portable solution to this
problem is known.
You should also be wary of common bugs in `eval' implementations.
In some shell implementations (e.g., older `ash', OpenBSD 3.8
`sh', `pdksh' v5.2.14 99/07/13.2, and `zsh' 4.2.5), the arguments
of `eval' are evaluated in a context where `$?' is 0, so they
exhibit behavior like this:
$ false; eval 'echo $?'
0
The correct behavior here is to output a nonzero value, but
portable scripts should not rely on this.
You should not rely on `LINENO' within `eval'. *Note Special
Shell Variables::.
`exit'
The default value of `exit' is supposed to be `$?'; unfortunately,
some shells, such as the DJGPP port of Bash 2.04, just perform
`exit 0'.
bash-2.04$ foo=`exit 1` || echo fail
fail
bash-2.04$ foo=`(exit 1)` || echo fail
fail
bash-2.04$ foo=`(exit 1); exit` || echo fail
bash-2.04$
Using `exit $?' restores the expected behavior.
Some shell scripts, such as those generated by `autoconf', use a
trap to clean up before exiting. If the last shell command exited
with nonzero status, the trap also exits with nonzero status so
that the invoker can tell that an error occurred.
Unfortunately, in some shells, such as Solaris `/bin/sh', an exit
trap ignores the `exit' command's argument. In these shells, a
trap cannot determine whether it was invoked by plain `exit' or by
`exit 1'. Instead of calling `exit' directly, use the
`AC_MSG_ERROR' macro that has a workaround for this problem.
`export'
The builtin `export' dubs a shell variable "environment variable".
Each update of exported variables corresponds to an update of the
environment variables. Conversely, each environment variable
received by the shell when it is launched should be imported as a
shell variable marked as exported.
Alas, many shells, such as Solaris `/bin/sh', IRIX 6.3, IRIX 5.2,
AIX 4.1.5, and Digital Unix 4.0, forget to `export' the
environment variables they receive. As a result, two variables
coexist: the environment variable and the shell variable. The
following code demonstrates this failure:
#!/bin/sh
echo $FOO
FOO=bar
echo $FOO
exec /bin/sh $0
when run with `FOO=foo' in the environment, these shells print
alternately `foo' and `bar', although they should print only `foo'
and then a sequence of `bar's.
Therefore you should `export' again each environment variable that
you update.
`false'
Don't expect `false' to exit with status 1: in native Solaris
`/bin/false' exits with status 255.
`for'
To loop over positional arguments, use:
for arg
do
echo "$arg"
done
You may _not_ leave the `do' on the same line as `for', since some
shells improperly grok:
for arg; do
echo "$arg"
done
If you want to explicitly refer to the positional arguments, given
the `$@' bug (*note Shell Substitutions::), use:
for arg in ${1+"$@"}; do
echo "$arg"
done
But keep in mind that Zsh, even in Bourne shell emulation mode,
performs word splitting on `${1+"$@"}'; see *Note Shell
Substitutions::, item `$@', for more.
`if'
Using `!' is not portable. Instead of:
if ! cmp -s file file.new; then
mv file.new file
fi
use:
if cmp -s file file.new; then :; else
mv file.new file
fi
There are shells that do not reset the exit status from an `if':
$ if (exit 42); then true; fi; echo $?
42
whereas a proper shell should have printed `0'. This is especially
bad in makefiles since it produces false failures. This is why
properly written makefiles, such as Automake's, have such hairy
constructs:
if test -f "$file"; then
install "$file" "$dest"
else
:
fi
`printf'
A format string starting with a `-' can cause problems. Bash
(e.g., 2.05b) interprets it as an options argument and gives an
error. And `--' to mark the end of options is not good in the
NetBSD Almquist shell (e.g., 0.4.6) which takes that literally as
the format string. Putting the `-' in a `%c' or `%s' is probably
the easiest way to avoid doubt,
printf %s -foo
`read'
Not all shells support `-r' (Solaris `/bin/sh' for example).
`pwd'
With modern shells, plain `pwd' outputs a "logical" directory
name, some of whose components may be symbolic links. These
directory names are in contrast to "physical" directory names,
whose components are all directories.
Posix 1003.1-2001 requires that `pwd' must support the `-L'
("logical") and `-P' ("physical") options, with `-L' being the
default. However, traditional shells do not support these
options, and their `pwd' command has the `-P' behavior.
Portable scripts should assume neither option is supported, and
should assume neither behavior is the default. Also, on many hosts
`/bin/pwd' is equivalent to `pwd -P', but Posix does not require
this behavior and portable scripts should not rely on it.
Typically it's best to use plain `pwd'. On modern hosts this
outputs logical directory names, which have the following
advantages:
* Logical names are what the user specified.
* Physical names may not be portable from one installation host
to another due to network file system gymnastics.
* On modern hosts `pwd -P' may fail due to lack of permissions
to some parent directory, but plain `pwd' cannot fail for this
reason.
Also please see the discussion of the `cd' command.
`set'
With the FreeBSD 6.0 shell, the `set' command (without any
options) does not sort its output.
The `set' builtin faces the usual problem with arguments starting
with a dash. Modern shells such as Bash or Zsh understand `--' to
specify the end of the options (any argument after `--' is a
parameter, even `-x' for instance), but many traditional shells
(e.g., Solaris 10 `/bin/sh') simply stop option processing as soon
as a non-option argument is found. Therefore, use `dummy' or
simply `x' to end the option processing, and use `shift' to pop it
out:
set x $my_list; shift
Avoid `set -', e.g., `set - $my_list'. Posix no longer requires
support for this command, and in traditional shells `set -
$my_list' resets the `-v' and `-x' options, which makes scripts
harder to debug.
Some nonstandard shells do not recognize more than one option
(e.g., `set -e -x' assigns `-x' to the command line). It is
better to combine them:
set -ex
The BSD shell has had several problems with the `-e' option,
partly because BSD `make' traditionally used `-e' even though this
was incompatible with Posix (*note Failure in Make Rules::).
Older versions of the BSD shell (circa 1990) mishandled `&&',
`||', `if', and `case' when `-e' was in effect, causing the shell
to exit unexpectedly in some cases. This was particularly a
problem with makefiles, and led to circumlocutions like `sh -c
'test -f file || touch file'', where the seemingly-unnecessary `sh
-c '...'' wrapper works around the bug.
Even relatively-recent versions of the BSD shell (e.g., OpenBSD
3.4) wrongly exit with `-e' if a command within `&&' fails inside
a compound statement. For example:
#! /bin/sh
set -e
foo=''
test -n "$foo" && exit 1
echo one
if :; then
test -n "$foo" && exit 1
fi
echo two
does not print `two'. One workaround is to use `if test -n
"$foo"; then exit 1; fi' rather than `test -n "$foo" && exit 1'.
Another possibility is to warn BSD users not to use `sh -e'.
`shift'
Not only is `shift'ing a bad idea when there is nothing left to
shift, but in addition it is not portable: the shell of MIPS
RISC/OS 4.52 refuses to do it.
Don't use `shift 2' etc.; it was not in the 7th Edition Bourne
shell, and it is also absent in many pre-Posix shells.
`source'
This command is not portable, as Posix does not require it; use
`.' instead.
`test'
The `test' program is the way to perform many file and string
tests. It is often invoked by the alternate name `[', but using
that name in Autoconf code is asking for trouble since it is an M4
quote character.
If you need to make multiple checks using `test', combine them with
the shell operators `&&' and `||' instead of using the `test'
operators `-a' and `-o'. On System V, the precedence of `-a' and
`-o' is wrong relative to the unary operators; consequently, Posix
does not specify them, so using them is nonportable. If you
combine `&&' and `||' in the same statement, keep in mind that
they have equal precedence.
It is safe to use `!' as a `test' operator. For example, `if test
! -d foo; ...' is portable even though `if ! test -d foo; ...' is
not.
`test' (files)
To enable `configure' scripts to support cross-compilation, they
shouldn't do anything that tests features of the build system
instead of the host system. But occasionally you may find it
necessary to check whether some arbitrary file exists. To do so,
use `test -f' or `test -r'. Do not use `test -x', because 4.3BSD
does not have it. Do not use `test -e' either, because Solaris
`/bin/sh' lacks it. To test for symbolic links on systems that
have them, use `test -h' rather than `test -L'; either form
conforms to Posix 1003.1-2001, but older shells like Solaris 8
`/bin/sh' support only `-h'.
`test' (strings)
Avoid `test "STRING"', in particular if STRING might start with a
dash, since `test' might interpret its argument as an option
(e.g., `STRING = "-n"').
Contrary to a common belief, `test -n STRING' and `test -z STRING'
*are* portable. Nevertheless many shells (such as Solaris, AIX
3.2, UNICOS 10.0.0.6, Digital Unix 4, etc.) have bizarre
precedence and may be confused if STRING looks like an operator:
$ test -n =
test: argument expected
If there are risks, use `test "xSTRING" = x' or `test "xSTRING" !=
x' instead.
It is common to find variations of the following idiom:
test -n "`echo $ac_feature | sed 's/[-a-zA-Z0-9_]//g'`" &&
ACTION
to take an action when a token matches a given pattern. Such
constructs should always be avoided by using:
echo "$ac_feature" | grep '[^-a-zA-Z0-9_]' >/dev/null 2>&1 &&
ACTION
Use `case' where possible since it is faster, being a shell
builtin:
case $ac_feature in
*[!-a-zA-Z0-9_]*) ACTION;;
esac
Alas, negated character classes are probably not portable,
although no shell is known to not support the Posix syntax `[!...]'
(when in interactive mode, `zsh' is confused by the `[!...]'
syntax and looks for an event in its history because of `!').
Many shells do not support the alternative syntax `[^...]'
(Solaris, Digital Unix, etc.).
One solution can be:
expr "$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
ACTION
or better yet
expr "X$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null &&
ACTION
`expr "XFOO" : "XBAR"' is more robust than `echo "XFOO" | grep
"^XBAR"', because it avoids problems when `FOO' contains
backslashes.
`trap'
It is safe to trap at least the signals 1, 2, 13, and 15. You can
also trap 0, i.e., have the `trap' run when the script ends
(either via an explicit `exit', or the end of the script). The
trap for 0 should be installed outside of a shell function, or AIX
5.3 `/bin/sh' will invoke the trap at the end of this function.
Posix says that `trap - 1 2 13 15' resets the traps for the
specified signals to their default values, but many common shells
(e.g., Solaris `/bin/sh') misinterpret this and attempt to execute
a "command" named `-' when the specified conditions arise. There
is no portable workaround, except for `trap - 0', for which `trap
'' 0' is a portable substitute.
Although Posix is not absolutely clear on this point, it is widely
admitted that when entering the trap `$?' should be set to the exit
status of the last command run before the trap. The ambiguity can
be summarized as: "when the trap is launched by an `exit', what is
the _last_ command run: that before `exit', or `exit' itself?"
Bash considers `exit' to be the last command, while Zsh and
Solaris `/bin/sh' consider that when the trap is run it is _still_
in the `exit', hence it is the previous exit status that the trap
receives:
$ cat trap.sh
trap 'echo $?' 0
(exit 42); exit 0
$ zsh trap.sh
42
$ bash trap.sh
0
The portable solution is then simple: when you want to `exit 42',
run `(exit 42); exit 42', the first `exit' being used to set the
exit status to 42 for Zsh, and the second to trigger the trap and
pass 42 as exit status for Bash.
The shell in FreeBSD 4.0 has the following bug: `$?' is reset to 0
by empty lines if the code is inside `trap'.
$ trap 'false
echo $?' 0
$ exit
0
Fortunately, this bug only affects `trap'.
`true'
Don't worry: as far as we know `true' is portable. Nevertheless,
it's not always a builtin (e.g., Bash 1.x), and the portable shell
community tends to prefer using `:'. This has a funny side
effect: when asked whether `false' is more portable than `true'
Alexandre Oliva answered:
In a sense, yes, because if it doesn't exist, the shell will
produce an exit status of failure, which is correct for
`false', but not for `true'.
`unset'
In some nonconforming shells (e.g., Bash 2.05a), `unset FOO' fails
when `FOO' is not set. Also, Bash 2.01 mishandles `unset MAIL' in
some cases and dumps core.
A few ancient shells lack `unset' entirely. Nevertheless, because
it is extremely useful to disable embarrassing variables such as
`PS1', you can test for its existence and use it _provided_ you
give a neutralizing value when `unset' is not supported:
# "|| exit" suppresses any "Segmentation fault" message.
if ( (MAIL=60; unset MAIL) || exit) >/dev/null 2>&1; then
unset=unset
else
unset=false
fi
$unset PS1 || PS1='$ '
*Note Special Shell Variables::, for some neutralizing values.
Also, see *Note Limitations of Builtins::, documentation of
`export', for the case of environment variables.

File: autoconf.info, Node: Limitations of Usual Tools, Prev: Limitations of Builtins, Up: Portable Shell
10.11 Limitations of Usual Tools
================================
The small set of tools you can expect to find on any machine can still
include some limitations you should be aware of.
Awk
Don't leave white space before the opening parenthesis in a user
function call. Posix does not allow this and GNU Awk rejects it:
$ gawk 'function die () { print "Aaaaarg!" }
BEGIN { die () }'
gawk: cmd. line:2: BEGIN { die () }
gawk: cmd. line:2: ^ parse error
$ gawk 'function die () { print "Aaaaarg!" }
BEGIN { die() }'
Aaaaarg!
If you want your program to be deterministic, don't depend on `for'
on arrays:
$ cat for.awk
END {
arr["foo"] = 1
arr["bar"] = 1
for (i in arr)
print i
}
$ gawk -f for.awk </dev/null
foo
bar
$ nawk -f for.awk </dev/null
bar
foo
Some Awk implementations, such as HP-UX 11.0's native one,
mishandle anchors:
$ echo xfoo | $AWK '/foo|^bar/ { print }'
$ echo bar | $AWK '/foo|^bar/ { print }'
bar
$ echo xfoo | $AWK '/^bar|foo/ { print }'
xfoo
$ echo bar | $AWK '/^bar|foo/ { print }'
bar
Either do not depend on such patterns (i.e., use `/^(.*foo|bar)/',
or use a simple test to reject such implementations.
AIX version 5.2 has an arbitrary limit of 399 on the length of
regular expressions and literal strings in an Awk program.
Traditional Awk implementations derived from Unix version 7, such
as Solaris `/bin/awk', have many limitations and do not conform to
Posix. Nowadays `AC_PROG_AWK' (*note Particular Programs::) finds
you an Awk that doesn't have these problems, but if for some
reason you prefer not to use `AC_PROG_AWK' you may need to address
them.
Traditional Awk does not support multidimensional arrays or
user-defined functions.
Traditional Awk does not support the `-v' option. You can use
assignments after the program instead, e.g., `$AWK '{print v $1}'
v=x'; however, don't forget that such assignments are not
evaluated until they are encountered (e.g., after any `BEGIN'
action).
Traditional Awk does not support the keywords `delete' or `do'.
Traditional Awk does not support the expressions `A?B:C', `!A',
`A^B', or `A^=B'.
Traditional Awk does not support the predefined `CONVFMT' variable.
Traditional Awk supports only the predefined functions `exp',
`int', `length', `log', `split', `sprintf', `sqrt', and `substr'.
Traditional Awk `getline' is not at all compatible with Posix;
avoid it.
Traditional Awk `split' supports only two arguments.
Traditional Awk has a limit of 99 fields in a record. You may be
able to circumvent this problem by using `split'.
`basename'
Not all hosts have a working `basename'. You can use `expr'
instead.
`cat'
Don't rely on any option.
`cc'
The command `cc -c foo.c' traditionally produces an object file
named `foo.o'. Most compilers allow `-c' to be combined with `-o'
to specify a different object file name, but Posix does not
require this combination and a few compilers lack support for it.
*Note C Compiler::, for how GNU Make tests for this feature with
`AC_PROG_CC_C_O'.
When a compilation such as `cc -o foo foo.c' fails, some compilers
(such as CDS on Reliant Unix) leave a `foo.o'.
HP-UX `cc' doesn't accept `.S' files to preprocess and assemble.
`cc -c foo.S' appears to succeed, but in fact does nothing.
The default executable, produced by `cc foo.c', can be
* `a.out' -- usual Posix convention.
* `b.out' -- i960 compilers (including `gcc').
* `a.exe' -- DJGPP port of `gcc'.
* `a_out.exe' -- GNV `cc' wrapper for DEC C on OpenVMS.
* `foo.exe' -- various MS-DOS compilers.
The C compiler's traditional name is `cc', but other names like
`gcc' are common. Posix 1003.1-2001 specifies the name `c99', but
older Posix editions specified `c89' and anyway these standard
names are rarely used in practice. Typically the C compiler is
invoked from makefiles that use `$(CC)', so the value of the `CC'
make variable selects the compiler name.
`chmod'
Avoid usages like `chmod -w file'; use `chmod a-w file' instead,
for two reasons. First, plain `-w' does not necessarily make the
file unwritable, since it does not affect mode bits that
correspond to bits in the file mode creation mask. Second, Posix
says that the `-w' might be interpreted as an
implementation-specific option, not as a mode; Posix suggests
using `chmod -- -w file' to avoid this confusion, but unfortunately
`--' does not work on some older hosts.
`cmp'
`cmp' performs a raw data comparison of two files, while `diff'
compares two text files. Therefore, if you might compare DOS
files, even if only checking whether two files are different, use
`diff' to avoid spurious differences due to differences of newline
encoding.
`cp'
Avoid the `-r' option, since Posix 1003.1-2004 marks it as
obsolescent and its behavior on special files is
implementation-defined. Use `-R' instead. On GNU hosts the two
options are equivalent, but on Solaris hosts (for example) `cp -r'
reads from pipes instead of replicating them.
Some `cp' implementations (e.g., BSD/OS 4.2) do not allow trailing
slashes at the end of nonexistent destination directories. To
avoid this problem, omit the trailing slashes. For example, use
`cp -R source /tmp/newdir' rather than `cp -R source /tmp/newdir/'
if `/tmp/newdir' does not exist.
The ancient SunOS 4 `cp' does not support `-f', although its `mv'
does.
Traditionally, file timestamps had 1-second resolution, and `cp
-p' copied the timestamps exactly. However, many modern file
systems have timestamps with 1-nanosecond resolution.
Unfortunately, `cp -p' implementations truncate timestamps when
copying files, so this can result in the destination file
appearing to be older than the source. The exact amount of
truncation depends on the resolution of the system calls that `cp'
uses; traditionally this was `utime', which has 1-second
resolution, but some newer `cp' implementations use `utimes',
which has 1-microsecond resolution. These newer implementations
include GNU Core Utilities 5.0.91 or later, and Solaris 8 (sparc)
patch 109933-02 or later. Unfortunately as of January 2006 there
is still no system call to set timestamps to the full nanosecond
resolution.
Bob Proulx notes that `cp -p' always _tries_ to copy ownerships.
But whether it actually does copy ownerships or not is a system
dependent policy decision implemented by the kernel. If the
kernel allows it then it happens. If the kernel does not allow it
then it does not happen. It is not something `cp' itself has
control over.
In Unix System V any user can chown files to any other user, and
System V also has a non-sticky `/tmp'. That probably derives from
the heritage of System V in a business environment without hostile
users. BSD changed this to be a more secure model where only root
can `chown' files and a sticky `/tmp' is used. That undoubtedly
derives from the heritage of BSD in a campus environment.
GNU/Linux and Solaris by default follow BSD, but can be configured
to allow a System V style `chown'. On the other hand, HP-UX
follows System V, but can be configured to use the modern security
model and disallow `chown'. Since it is an
administrator-configurable parameter you can't use the name of the
kernel as an indicator of the behavior.
`date'
Some versions of `date' do not recognize special `%' directives,
and unfortunately, instead of complaining, they just pass them
through, and exit with success:
$ uname -a
OSF1 medusa.sis.pasteur.fr V5.1 732 alpha
$ date "+%s"
%s
`diff'
Option `-u' is nonportable.
Some implementations, such as Tru64's, fail when comparing to
`/dev/null'. Use an empty file instead.
`dirname'
Not all hosts have a working `dirname', and you should instead use
`AS_DIRNAME' (*note Programming in M4sh::). For example:
dir=`dirname "$file"` # This is not portable.
dir=`AS_DIRNAME(["$file"])` # This is more portable.
`egrep'
Posix 1003.1-2001 no longer requires `egrep', but many older hosts
do not yet support the Posix replacement `grep -E'. Also, some
traditional implementations do not work on long input lines. To
work around these problems, invoke `AC_PROG_EGREP' and then use
`$EGREP'.
Portable extended regular expressions should use `\' only to escape
characters in the string `$()*+.?[\^{|'. For example, `\}' is not
portable, even though it typically matches `}'.
The empty alternative is not portable. Use `?' instead. For
instance with Digital Unix v5.0:
> printf "foo\n|foo\n" | $EGREP '^(|foo|bar)$'
|foo
> printf "bar\nbar|\n" | $EGREP '^(foo|bar|)$'
bar|
> printf "foo\nfoo|\n|bar\nbar\n" | $EGREP '^(foo||bar)$'
foo
|bar
`$EGREP' also suffers the limitations of `grep'.
`expr'
No `expr' keyword starts with `X', so use `expr X"WORD" :
'XREGEX'' to keep `expr' from misinterpreting WORD.
Don't use `length', `substr', `match' and `index'.
`expr' (`|')
You can use `|'. Although Posix does require that `expr '''
return the empty string, it does not specify the result when you
`|' together the empty string (or zero) with the empty string. For
example:
expr '' \| ''
Posix 1003.2-1992 returns the empty string for this case, but
traditional Unix returns `0' (Solaris is one such example). In
Posix 1003.1-2001, the specification was changed to match
traditional Unix's behavior (which is bizarre, but it's too late
to fix this). Please note that the same problem does arise when
the empty string results from a computation, as in:
expr bar : foo \| foo : bar
Avoid this portability problem by avoiding the empty string.
`expr' (`:')
Portable `expr' regular expressions should use `\' to escape only
characters in the string `$()*.0123456789[\^n{}'. For example,
alternation, `\|', is common but Posix does not require its
support, so it should be avoided in portable scripts. Similarly,
`\+' and `\?' should be avoided.
Portable `expr' regular expressions should not begin with `^'.
Patterns are automatically anchored so leading `^' is not needed
anyway.
The Posix standard is ambiguous as to whether `expr 'a' : '\(b\)''
outputs `0' or the empty string. In practice, it outputs the
empty string on most platforms, but portable scripts should not
assume this. For instance, the QNX 4.25 native `expr' returns `0'.
One might think that a way to get a uniform behavior would be to
use the empty string as a default value:
expr a : '\(b\)' \| ''
Unfortunately this behaves exactly as the original expression; see
the `expr' (`|') entry for more information.
Ancient `expr' implementations (e.g., SunOS 4 `expr' and Solaris 8
`/usr/ucb/expr') have a silly length limit that causes `expr' to
fail if the matched substring is longer than 120 bytes. In this
case, you might want to fall back on `echo|sed' if `expr' fails.
Nowadays this is of practical importance only for the rare
installer who mistakenly puts `/usr/ucb' before `/usr/bin' in
`PATH'.
On Mac OS X 10.4, `expr' mishandles the pattern `[^-]' in some
cases. For example, the command
expr Xpowerpc-apple-darwin8.1.0 : 'X[^-]*-[^-]*-\(.*\)'
outputs `apple-darwin8.1.0' rather than the correct `darwin8.1.0'.
This particular case can be worked around by substituting `[^--]'
for `[^-]'.
Don't leave, there is some more!
The QNX 4.25 `expr', in addition of preferring `0' to the empty
string, has a funny behavior in its exit status: it's always 1
when parentheses are used!
$ val=`expr 'a' : 'a'`; echo "$?: $val"
0: 1
$ val=`expr 'a' : 'b'`; echo "$?: $val"
1: 0
$ val=`expr 'a' : '\(a\)'`; echo "?: $val"
1: a
$ val=`expr 'a' : '\(b\)'`; echo "?: $val"
1: 0
In practice this can be a big problem if you are ready to catch
failures of `expr' programs with some other method (such as using
`sed'), since you may get twice the result. For instance
$ expr 'a' : '\(a\)' || echo 'a' | sed 's/^\(a\)$/\1/'
outputs `a' on most hosts, but `aa' on QNX 4.25. A simple
workaround consists of testing `expr' and using a variable set to
`expr' or to `false' according to the result.
Tru64 `expr' incorrectly treats the result as a number, if it can
be interpreted that way:
$ expr 00001 : '.*\(...\)'
1
`fgrep'
Posix 1003.1-2001 no longer requires `fgrep', but many older hosts
do not yet support the Posix replacement `grep -F'. Also, some
traditional implementations do not work on long input lines. To
work around these problems, invoke `AC_PROG_FGREP' and then use
`$FGREP'.
`find'
The option `-maxdepth' seems to be GNU specific. Tru64 v5.1,
NetBSD 1.5 and Solaris `find' commands do not understand it.
The replacement of `{}' is guaranteed only if the argument is
exactly _{}_, not if it's only a part of an argument. For
instance on DU, and HP-UX 10.20 and HP-UX 11:
$ touch foo
$ find . -name foo -exec echo "{}-{}" \;
{}-{}
while GNU `find' reports `./foo-./foo'.
`grep'
Portable scripts can rely on the `grep' options `-c', `-l', `-n',
and `-v', but should avoid other options. For example, don't use
`-w', as Posix does not require it and Irix 6.5.16m's `grep' does
not support it. Also, portable scripts should not combine `-c'
with `-l', as Posix does not allow this.
Some of the options required by Posix are not portable in practice.
Don't use `grep -q' to suppress output, because many `grep'
implementations (e.g., Solaris) do not support `-q'. Don't use
`grep -s' to suppress output either, because Posix says `-s' does
not suppress output, only some error messages; also, the `-s'
option of traditional `grep' behaved like `-q' does in most modern
implementations. Instead, redirect the standard output and
standard error (in case the file doesn't exist) of `grep' to
`/dev/null'. Check the exit status of `grep' to determine whether
it found a match.
Some traditional `grep' implementations do not work on long input
lines. On AIX the default `grep' silently truncates long lines on
the input before matching.
Also, many implementations do not support multiple regexps with
`-e': they either reject `-e' entirely (e.g., Solaris) or honor
only the last pattern (e.g., IRIX 6.5 and NeXT). To work around
these problems, invoke `AC_PROG_GREP' and then use `$GREP'.
Another possible workaround for the multiple `-e' problem is to
separate the patterns by newlines, for example:
grep 'foo
bar' in.txt
except that this fails with traditional `grep' implementations and
with OpenBSD 3.8 `grep'.
Traditional `grep' implementations (e.g., Solaris) do not support
the `-E' or `-F' options. To work around these problems, invoke
`AC_PROG_EGREP' and then use `$EGREP', and similarly for
`AC_PROG_FGREP' and `$FGREP'. Even if you are willing to require
support for Posix `grep', your script should not use both `-E' and
`-F', since Posix does not allow this combination.
Portable `grep' regular expressions should use `\' only to escape
characters in the string `$()*.0123456789[\^{}'. For example,
alternation, `\|', is common but Posix does not require its
support in basic regular expressions, so it should be avoided in
portable scripts. Solaris `grep' does not support it. Similarly,
`\+' and `\?' should be avoided.
`join'
Solaris 8 `join' has bugs when the second operand is standard
input, and when standard input is a pipe. For example, the
following shell script causes Solaris 8 `join' to loop forever:
cat >file <<'EOF'
1 x
2 y
EOF
cat file | join file -
Use `join - file' instead.
`ln'
Don't rely on `ln' having a `-f' option. Symbolic links are not
available on old systems; use `$(LN_S)' as a portable substitute.
For versions of the DJGPP before 2.04, `ln' emulates symbolic links
to executables by generating a stub that in turn calls the real
program. This feature also works with nonexistent files like in
the Posix spec. So `ln -s file link' generates `link.exe', which
attempts to call `file.exe' if run. But this feature only works
for executables, so `cp -p' is used instead for these systems.
DJGPP versions 2.04 and later have full support for symbolic links.
`ls'
The portable options are `-acdilrtu'. Current practice is for
`-l' to output both owner and group, even though ancient versions
of `ls' omitted the group.
On ancient hosts, `ls foo' sent the diagnostic `foo not found' to
standard output if `foo' did not exist. Hence a shell command
like `sources=`ls *.c 2>/dev/null`' did not always work, since it
was equivalent to `sources='*.c not found'' in the absence of `.c'
files. This is no longer a practical problem, since current `ls'
implementations send diagnostics to standard error.
`mkdir'
No `mkdir' option is portable to older systems. Instead of `mkdir
-p FILE-NAME', you should use `AS_MKDIR_P(FILE-NAME)' (*note
Programming in M4sh::) or `AC_PROG_MKDIR_P' (*note Particular
Programs::).
Combining the `-m' and `-p' options, as in `mkdir -m go-w -p DIR',
often leads to trouble. FreeBSD `mkdir' incorrectly attempts to
change the permissions of DIR even if it already exists. HP-UX
11.23 and IRIX 6.5 `mkdir' often assign the wrong permissions to
any newly-created parents of DIR.
Posix does not clearly specify whether `mkdir -p foo' should
succeed when `foo' is a symbolic link to an already-existing
directory. The GNU Core Utilities 5.1.0 `mkdir' succeeds, but
Solaris `mkdir' fails.
Traditional `mkdir -p' implementations suffer from race conditions.
For example, if you invoke `mkdir -p a/b' and `mkdir -p a/c' at
the same time, both processes might detect that `a' is missing,
one might create `a', then the other might try to create `a' and
fail with a `File exists' diagnostic. The GNU Core Utilities
(`fileutils' version 4.1), FreeBSD 5.0, NetBSD 2.0.2, and OpenBSD
2.4 are known to be race-free when two processes invoke `mkdir -p'
simultaneously, but earlier versions are vulnerable. Solaris
`mkdir' is still vulnerable as of Solaris 10, and other
traditional Unix systems are probably vulnerable too. This
possible race is harmful in parallel builds when several Make
rules call `mkdir -p' to construct directories. You may use
`install-sh -d' as a safe replacement, provided this script is
recent enough; the copy shipped with Autoconf 2.60 and Automake
1.10 is OK, but copies from older versions are vulnerable.
`mktemp'
Shell scripts can use temporary files safely with `mktemp', but it
does not exist on all systems. A portable way to create a safe
temporary file name is to create a temporary directory with mode
700 and use a file inside this directory. Both methods prevent
attackers from gaining control, though `mktemp' is far less likely
to fail gratuitously under attack.
Here is sample code to create a new temporary directory safely:
# Create a temporary directory $tmp in $TMPDIR (default /tmp).
# Use mktemp if possible; otherwise fall back on mkdir,
# with $RANDOM to make collisions less likely.
: ${TMPDIR=/tmp}
{
tmp=`
(umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null
` &&
test -n "$tmp" && test -d "$tmp"
} || {
tmp=$TMPDIR/foo$$-$RANDOM
(umask 077 && mkdir "$tmp")
} || exit $?
`mv'
The only portable options are `-f' and `-i'.
Moving individual files between file systems is portable (it was
in Unix version 6), but it is not always atomic: when doing `mv
new existing', there's a critical section where neither the old
nor the new version of `existing' actually exists.
On some systems moving files from `/tmp' can sometimes cause
undesirable (but perfectly valid) warnings, even if you created
these files. This is because `/tmp' belongs to a group that
ordinary users are not members of, and files created in `/tmp'
inherit the group of `/tmp'. When the file is copied, `mv' issues
a diagnostic without failing:
$ touch /tmp/foo
$ mv /tmp/foo .
error-->mv: ./foo: set owner/group (was: 100/0): Operation not permitted
$ echo $?
0
$ ls foo
foo
This annoying behavior conforms to Posix, unfortunately.
Moving directories across mount points is not portable, use `cp'
and `rm'.
DOS variants cannot rename or remove open files, and do not
support commands like `mv foo bar >foo', even though this is
perfectly portable among Posix hosts.
`od'
In Mac OS X 10.3, `od' does not support the standard Posix options
`-A', `-j', `-N', or `-t', or the XSI option `-s'. The only
supported Posix option is `-v', and the only supported XSI options
are those in `-bcdox'. The BSD `hexdump' program can be used
instead.
This problem no longer exists in Mac OS X 10.4.3.
`rm'
The `-f' and `-r' options are portable.
It is not portable to invoke `rm' without operands. For example,
on many systems `rm -f -r' (with no other arguments) silently
succeeds without doing anything, but it fails with a diagnostic on
NetBSD 2.0.2.
A file might not be removed even if its parent directory is
writable and searchable. Many Posix hosts cannot remove a mount
point, a named stream, a working directory, or a last link to a
file that is being executed.
DOS variants cannot rename or remove open files, and do not
support commands like `rm foo >foo', even though this is perfectly
portable among Posix hosts.
`sed'
Patterns should not include the separator (unless escaped), even
as part of a character class. In conformance with Posix, the Cray
`sed' rejects `s/[^/]*$//': use `s,[^/]*$,,'.
Avoid empty patterns within parentheses (i.e., `\(\)'). Posix does
not require support for empty patterns, and Unicos 9 `sed' rejects
them.
Unicos 9 `sed' loops endlessly on patterns like `.*\n.*'.
Sed scripts should not use branch labels longer than 8 characters
and should not contain comments. HP-UX sed has a limit of 99
commands (not counting `:' commands) and 48 labels, which can not
be circumvented by using more than one script file. It can
execute up to 19 reads with the `r' command per cycle. Solaris
`/usr/ucb/sed' rejects usages that exceed an limit of about 6000
bytes for the internal representation of commands.
Avoid redundant `;', as some `sed' implementations, such as NetBSD
1.4.2's, incorrectly try to interpret the second `;' as a command:
$ echo a | sed 's/x/x/;;s/x/x/'
sed: 1: "s/x/x/;;s/x/x/": invalid command code ;
Input should not have unreasonably long lines, since some `sed'
implementations have an input buffer limited to 4000 bytes.
Portable `sed' regular expressions should use `\' only to escape
characters in the string `$()*.0123456789[\^n{}'. For example,
alternation, `\|', is common but Posix does not require its
support, so it should be avoided in portable scripts. Solaris
`sed' does not support alternation; e.g., `sed '/a\|b/d'' deletes
only lines that contain the literal string `a|b'. Similarly, `\+'
and `\?' should be avoided.
Anchors (`^' and `$') inside groups are not portable.
Nested parenthesization in patterns (e.g., `\(\(a*\)b*)\)') is
quite portable to current hosts, but was not supported by some
ancient `sed' implementations like SVR3.
Some `sed' implementations, e.g., Solaris, restrict the special
role of the asterisk to one-character regular expressions. This
may lead to unexpected behavior:
$ echo '1*23*4' | /usr/bin/sed 's/\(.\)*/x/g'
x2x4
$ echo '1*23*4' | /usr/xpg4/bin/sed 's/\(.\)*/x/g'
x
The `-e' option is portable, so long as its argument does not
begin with `a', `c', or `i' (as this runs afoul of a Tru64 5.1
bug). Some people prefer to use `-e':
sed -e 'COMMAND-1' \
-e 'COMMAND-2'
as opposed to the equivalent:
sed '
COMMAND-1
COMMAND-2
'
The following usage is sometimes equivalent:
sed 'COMMAND-1;COMMAND-2'
but Posix says that this use of a semicolon has undefined effect if
COMMAND-1's verb is `{', `a', `b', `c', `i', `r', `t', `w', `:',
or `#', so you should use semicolon only with simple scripts that
do not use these verbs.
Commands inside { } brackets are further restricted. Posix says
that they cannot be preceded by addresses, `!', or `;', and that
each command must be followed immediately by a newline, without any
intervening blanks or semicolons. The closing bracket must be
alone on a line, other than white space preceding or following it.
Contrary to yet another urban legend, you may portably use `&' in
the replacement part of the `s' command to mean "what was
matched". All descendants of Unix version 7 `sed' (at least; we
don't have first hand experience with older `sed' implementations)
have supported it.
Posix requires that you must not have any white space between `!'
and the following command. It is OK to have blanks between the
address and the `!'. For instance, on Solaris:
$ echo "foo" | sed -n '/bar/ ! p'
error-->Unrecognized command: /bar/ ! p
$ echo "foo" | sed -n '/bar/! p'
error-->Unrecognized command: /bar/! p
$ echo "foo" | sed -n '/bar/ !p'
foo
Posix also says that you should not combine `!' and `;'. If you
use `!', it is best to put it on a command that is delimited by
newlines rather than `;'.
Also note that Posix requires that the `b', `t', `r', and `w'
commands be followed by exactly one space before their argument.
On the other hand, no white space is allowed between `:' and the
subsequent label name.
If a sed script is specified on the command line and ends in an
`a', `c', or `i' command, the last line of inserted text should be
followed by a newline. Otherwise some `sed' implementations
(e.g., OpenBSD 3.9) do not append a newline to the inserted text.
Many `sed' implementations (e.g., MacOS X 10.4, OpenBSD 3.9,
Solaris 10 `/usr/ucb/sed') strip leading white space from the text
of `a', `c', and `i' commands. Prepend a backslash to work around
this incompatibility with Posix:
$ echo flushleft | sed 'a\
> indented
> '
flushleft
indented
$ echo foo | sed 'a\
> \ indented
> '
flushleft
indented
`sed' (`t')
Some old systems have `sed' that "forget" to reset their `t' flag
when starting a new cycle. For instance on MIPS RISC/OS, and on
IRIX 5.3, if you run the following `sed' script (the line numbers
are not actual part of the texts):
s/keep me/kept/g # a
t end # b
s/.*/deleted/g # c
:end # d
on
delete me # 1
delete me # 2
keep me # 3
delete me # 4
you get
deleted
delete me
kept
deleted
instead of
deleted
deleted
kept
deleted
Why? When processing line 1, (c) matches, therefore sets the `t'
flag, and the output is produced. When processing line 2, the `t'
flag is still set (this is the bug). Command (a) fails to match,
but `sed' is not supposed to clear the `t' flag when a
substitution fails. Command (b) sees that the flag is set,
therefore it clears it, and jumps to (d), hence you get `delete me'
instead of `deleted'. When processing line (3), `t' is clear, (a)
matches, so the flag is set, hence (b) clears the flags and jumps.
Finally, since the flag is clear, line 4 is processed properly.
There are two things one should remember about `t' in `sed'.
Firstly, always remember that `t' jumps if _some_ substitution
succeeded, not only the immediately preceding substitution.
Therefore, always use a fake `t clear' followed by a `:clear' on
the next line, to reset the `t' flag where needed.
Secondly, you cannot rely on `sed' to clear the flag at each new
cycle.
One portable implementation of the script above is:
t clear
:clear
s/keep me/kept/g
t end
s/.*/deleted/g
:end
`touch'
If you specify the desired timestamp (e.g., with the `-r' option),
`touch' typically uses the `utime' or `utimes' system call, which
can result in the same kind of timestamp truncation problems that
`cp -p' has.
On ancient BSD systems, `touch' or any command that results in an
empty file does not update the timestamps, so use a command like
`echo' as a workaround. Also, GNU `touch' 3.16r (and presumably
all before that) fails to work on SunOS 4.1.3 when the empty file
is on an NFS-mounted 4.2 volume. However, these problems are no
longer of practical concern.

File: autoconf.info, Node: Portable Make, Next: Portable C and C++, Prev: Portable Shell, Up: Top
11 Portable Make Programming
****************************
Writing portable makefiles is an art. Since a makefile's commands are
executed by the shell, you must consider the shell portability issues
already mentioned. However, other issues are specific to `make' itself.
* Menu:
* $< in Ordinary Make Rules:: $< in ordinary rules
* Failure in Make Rules:: Failing portably in rules
* Special Chars in Names:: Special Characters in Macro Names
* Backslash-Newline-Newline:: Empty last lines in macro definitions
* Backslash-Newline Comments:: Spanning comments across line boundaries
* Long Lines in Makefiles:: Line length limitations
* Macros and Submakes:: `make macro=value' and submakes
* The Make Macro MAKEFLAGS:: `$(MAKEFLAGS)' portability issues
* The Make Macro SHELL:: `$(SHELL)' portability issues
* Comments in Make Rules:: Other problems with Make comments
* obj/ and Make:: Don't name a subdirectory `obj'
* make -k Status:: Exit status of `make -k'
* VPATH and Make:: `VPATH' woes
* Single Suffix Rules:: Single suffix rules and separated dependencies
* Timestamps and Make:: Subsecond timestamp resolution

File: autoconf.info, Node: $< in Ordinary Make Rules, Next: Failure in Make Rules, Up: Portable Make
11.1 `$<' in Ordinary Make Rules
================================
Posix says that the `$<' construct in makefiles can be used only in
inference rules and in the `.DEFAULT' rule; its meaning in ordinary
rules is unspecified. Solaris `make' for instance replaces it with the
empty string. OpenBSD (3.0 and later) `make' diagnoses these uses and
errors out.

File: autoconf.info, Node: Failure in Make Rules, Next: Special Chars in Names, Prev: $< in Ordinary Make Rules, Up: Portable Make
11.2 Failure in Make Rules
==========================
Since 1992 Posix has required that `make' must invoke each command with
the equivalent of a `sh -c' subshell. However, many `make'
implementations, including BSD make through 2004, use `sh -e -c'
instead, and the `-e' option causes the subshell to exit immediately if
a subsidiary simple-command fails. For example, the command `touch T;
rm -f U' always attempts to remove `U' with Posix make, but incompatible
`make' implementations skip the `rm' if the `touch' fails. One way to
work around this is to reword the affected simple-commands so that they
always succeed, e.g., `touch T || :; rm -f U'. However, even this
approach can run into common bugs in BSD implementations of the `-e'
option of `sh' and `set' (*note Limitations of Builtins::), so if you
are worried about porting to buggy BSD shells it may be simpler to
migrate complicated `make' actions into separate scripts.

File: autoconf.info, Node: Special Chars in Names, Next: Backslash-Newline-Newline, Prev: Failure in Make Rules, Up: Portable Make
11.3 Special Characters in Make Macro Names
===========================================
Posix limits macro names to nonempty strings containing only ASCII
letters and digits, `.', and `_'. Many `make' implementations allow a
wider variety of characters, but portable makefiles should avoid them.
It is portable to start a name with a special character, e.g.,
`$(.FOO)'.
Some ancient `make' implementations don't support leading
underscores in macro names. An example is NEWS-OS 4.2R.
$ cat Makefile
_am_include = #
_am_quote =
all:; @echo this is test
$ make
Make: Must be a separator on rules line 2. Stop.
$ cat Makefile2
am_include = #
am_quote =
all:; @echo this is test
$ make -f Makefile2
this is test
However, this problem is no longer of practical concern.

File: autoconf.info, Node: Backslash-Newline-Newline, Next: Backslash-Newline Comments, Prev: Special Chars in Names, Up: Portable Make
11.4 Backslash-Newline-Newline in Make Macro Values
===================================================
On some versions of HP-UX, `make' reads multiple newlines following a
backslash, continuing to the next non-empty line. For example,
FOO = one \
BAR = two
test:
: FOO is "$(FOO)"
: BAR is "$(BAR)"
shows `FOO' equal to `one BAR = two'. Other implementations sensibly
let a backslash continue only to the immediately following line.

File: autoconf.info, Node: Backslash-Newline Comments, Next: Long Lines in Makefiles, Prev: Backslash-Newline-Newline, Up: Portable Make
11.5 Backslash-Newline in Make Comments
=======================================
According to Posix, Make comments start with `#' and continue until an
unescaped newline is reached.
$ cat Makefile
# A = foo \
bar \
baz
all:
@echo ok
$ make # GNU make
ok
However this is not always the case. Some implementations discard
everything from `#' through the end of the line, ignoring any trailing
backslash.
$ pmake # BSD make
"Makefile", line 3: Need an operator
Fatal errors encountered -- cannot continue
Therefore, if you want to comment out a multi-line definition, prefix
each line with `#', not only the first.
# A = foo \
# bar \
# baz

File: autoconf.info, Node: Long Lines in Makefiles, Next: Macros and Submakes, Prev: Backslash-Newline Comments, Up: Portable Make
11.6 Long Lines in Makefiles
============================
Tru64 5.1's `make' has been reported to crash when given a makefile
with lines longer than around 20 kB. Earlier versions are reported to
exit with `Line too long' diagnostics.

File: autoconf.info, Node: Macros and Submakes, Next: The Make Macro MAKEFLAGS, Prev: Long Lines in Makefiles, Up: Portable Make
11.7 `make macro=value' and Submakes
====================================
A command-line variable definition such as `foo=bar' overrides any
definition of `foo' in a makefile. Some `make' implementations (such
as GNU `make') propagate this override to subsidiary invocations of
`make'. Some other implementations do not pass the substitution along
to submakes.
$ cat Makefile
foo = foo
one:
@echo $(foo)
$(MAKE) two
two:
@echo $(foo)
$ make foo=bar # GNU make 3.79.1
bar
make two
make[1]: Entering directory `/home/adl'
bar
make[1]: Leaving directory `/home/adl'
$ pmake foo=bar # BSD make
bar
pmake two
foo
You have a few possibilities if you do want the `foo=bar' override
to propagate to submakes. One is to use the `-e' option, which causes
all environment variables to have precedence over the makefile macro
definitions, and declare foo as an environment variable:
$ env foo=bar make -e
The `-e' option is propagated to submakes automatically, and since
the environment is inherited between `make' invocations, the `foo'
macro is overridden in submakes as expected.
This syntax (`foo=bar make -e') is portable only when used outside
of a makefile, for instance from a script or from the command line.
When run inside a `make' rule, GNU `make' 3.80 and prior versions
forget to propagate the `-e' option to submakes.
Moreover, using `-e' could have unexpected side effects if your
environment contains some other macros usually defined by the makefile.
(See also the note about `make -e' and `SHELL' below.)
Another way to propagate overrides to submakes is to do it manually,
from your makefile:
foo = foo
one:
@echo $(foo)
$(MAKE) foo=$(foo) two
two:
@echo $(foo)
You need to foresee all macros that a user might want to override if
you do that.

File: autoconf.info, Node: The Make Macro MAKEFLAGS, Next: The Make Macro SHELL, Prev: Macros and Submakes, Up: Portable Make
11.8 The Make Macro MAKEFLAGS
=============================
Posix requires `make' to use `MAKEFLAGS' to affect the current and
recursive invocations of make, but allows implementations several
formats for the variable. It is tricky to parse `$MAKEFLAGS' to
determine whether `-s' for silent execution or `-k' for continued
execution are in effect. For example, you cannot assume that the first
space-separated word in `$MAKEFLAGS' contains single-letter options,
since in the Cygwin version of GNU `make' it is either `--unix' or
`--win32' with the second word containing single-letter options.
$ cat Makefile
all:
@echo MAKEFLAGS = $(MAKEFLAGS)
$ make
MAKEFLAGS = --unix
$ make -k
MAKEFLAGS = --unix -k

File: autoconf.info, Node: The Make Macro SHELL, Next: Comments in Make Rules, Prev: The Make Macro MAKEFLAGS, Up: Portable Make
11.9 The Make Macro `SHELL'
===========================
Posix-compliant `make' internally uses the `$(SHELL)' macro to spawn
shell processes and execute Make rules. This is a builtin macro
supplied by `make', but it can be modified by a makefile or by a
command-line argument.
Not all `make' implementations define this `SHELL' macro. Tru64
`make' is an example; this implementation always uses `/bin/sh'. So
it's a good idea to always define `SHELL' in your makefiles. If you
use Autoconf, do
SHELL = @SHELL@
Do not force `SHELL = /bin/sh' because that is not correct
everywhere. For instance DJGPP lacks `/bin/sh', and when its GNU
`make' port sees such a setting it enters a special emulation mode
where features like pipes and redirections are emulated on top of DOS's
`command.com'. Unfortunately this emulation is incomplete; for
instance it does not handle command substitutions. On DJGPP `SHELL'
should point to Bash.
Posix-compliant `make' should never acquire the value of $(SHELL)
from the environment, even when `make -e' is used (otherwise, think
about what would happen to your rules if `SHELL=/bin/tcsh').
However not all `make' implementations have this exception. For
instance it's not surprising that Tru64 `make' doesn't protect `SHELL',
since it doesn't use it.
$ cat Makefile
SHELL = /bin/sh
FOO = foo
all:
@echo $(SHELL)
@echo $(FOO)
$ env SHELL=/bin/tcsh FOO=bar make -e # Tru64 Make
/bin/tcsh
bar
$ env SHELL=/bin/tcsh FOO=bar gmake -e # GNU make
/bin/sh
bar

File: autoconf.info, Node: Comments in Make Rules, Next: obj/ and Make, Prev: The Make Macro SHELL, Up: Portable Make
11.10 Comments in Make Rules
============================
Never put comments in a rule.
Some `make' treat anything starting with a tab as a command for the
current rule, even if the tab is immediately followed by a `#'. The
`make' from Tru64 Unix V5.1 is one of them. The following makefile
runs `# foo' through the shell.
all:
# foo

File: autoconf.info, Node: obj/ and Make, Next: make -k Status, Prev: Comments in Make Rules, Up: Portable Make
11.11 The `obj/' Subdirectory and Make
======================================
Never name one of your subdirectories `obj/' if you don't like
surprises.
If an `obj/' directory exists, BSD `make' enters it before reading
the makefile. Hence the makefile in the current directory is not read.
$ cat Makefile
all:
echo Hello
$ cat obj/Makefile
all:
echo World
$ make # GNU make
echo Hello
Hello
$ pmake # BSD make
echo World
World

File: autoconf.info, Node: make -k Status, Next: VPATH and Make, Prev: obj/ and Make, Up: Portable Make
11.12 Exit Status of `make -k'
==============================
Do not rely on the exit status of `make -k'. Some implementations
reflect whether they encountered an error in their exit status; other
implementations always succeed.
$ cat Makefile
all:
false
$ make -k; echo exit status: $? # GNU make
false
make: *** [all] Error 1
exit status: 2
$ pmake -k; echo exit status: $? # BSD make
false
*** Error code 1 (continuing)
exit status: 0

File: autoconf.info, Node: VPATH and Make, Next: Single Suffix Rules, Prev: make -k Status, Up: Portable Make
11.13 `VPATH' and Make
======================
Posix does not specify the semantics of `VPATH'. Typically, `make'
supports `VPATH', but its implementation is not consistent.
Autoconf and Automake support makefiles whose usages of `VPATH' are
portable to recent-enough popular implementations of `make', but to
keep the resulting makefiles portable, a package's makefile prototypes
must take the following issues into account. These issues are
complicated and are often poorly understood, and installers who use
`VPATH' should expect to find many bugs in this area. If you use
`VPATH', the simplest way to avoid these portability bugs is to stick
with GNU `make', since it is the most commonly-used `make' among
Autoconf users.
Here are some known issues with some `VPATH' implementations.
* Menu:
* VPATH and Double-colon:: Problems with `::' on ancient hosts
* $< in Explicit Rules:: `$<' does not work in ordinary rules
* Automatic Rule Rewriting:: `VPATH' goes wild on Solaris
* Tru64 Directory Magic:: `mkdir' goes wild on Tru64
* Make Target Lookup:: More details about `VPATH' lookup

File: autoconf.info, Node: VPATH and Double-colon, Next: $< in Explicit Rules, Up: VPATH and Make
11.13.1 `VPATH' and Double-colon Rules
--------------------------------------
With ancient versions of Sun `make', any assignment to `VPATH' causes
`make' to execute only the first set of double-colon rules. However,
this problem is no longer of practical concern.

File: autoconf.info, Node: $< in Explicit Rules, Next: Automatic Rule Rewriting, Prev: VPATH and Double-colon, Up: VPATH and Make
11.13.2 `$<' Not Supported in Explicit Rules
--------------------------------------------
Using `$<' in explicit rules is not portable. The prerequisite file
must be named explicitly in the rule. If you want to find the
prerequisite via a `VPATH' search, you have to code the whole thing
manually. *Note Build Directories::.

File: autoconf.info, Node: Automatic Rule Rewriting, Next: Tru64 Directory Magic, Prev: $< in Explicit Rules, Up: VPATH and Make
11.13.3 Automatic Rule Rewriting
--------------------------------
Some `make' implementations, such as Solaris and Tru64, search for
prerequisites in `VPATH' and then rewrite each occurrence as a plain
word in the rule. For instance:
# This isn't portable to GNU make.
VPATH = ../pkg/src
f.c: if.c
cp if.c f.c
executes `cp ../pkg/src/if.c f.c' if `if.c' is found in `../pkg/src'.
However, this rule leads to real problems in practice. For example,
if the source directory contains an ordinary file named `test' that is
used in a dependency, Solaris `make' rewrites commands like `if test -r
foo; ...' to `if ../pkg/src/test -r foo; ...', which is typically
undesirable. To avoid this problem, portable makefiles should never
mention a source file whose name is that of a shell keyword like
`until' or a shell command like `cat' or `gcc' or `test'.
Because of these problems GNU `make' and many other `make'
implementations do not rewrite commands, so portable makefiles should
search `VPATH' manually. It is tempting to write this:
# This isn't portable to Solaris make.
VPATH = ../pkg/src
f.c: if.c
cp `test -f if.c || echo $(VPATH)/`if.c f.c
However, the "prerequisite rewriting" still applies here. So if `if.c'
is in `../pkg/src', Solaris and Tru64 `make' execute
cp `test -f ../pkg/src/if.c || echo ../pkg/src/`if.c f.c
which reduces to
cp if.c f.c
and thus fails. Oops.
A simple workaround, and good practice anyway, is to use `$?' and
`$@' when possible:
VPATH = ../pkg/src
f.c: if.c
cp $? $@
but this does not generalize well to commands with multiple
prerequisites. A more general workaround is to rewrite the rule so that
the prerequisite `if.c' never appears as a plain word. For example,
these three rules would be safe, assuming `if.c' is in `../pkg/src' and
the other files are in the working directory:
VPATH = ../pkg/src
f.c: if.c f1.c
cat `test -f ./if.c || echo $(VPATH)/`if.c f1.c >$@
g.c: if.c g1.c
cat `test -f 'if.c' || echo $(VPATH)/`if.c g1.c >$@
h.c: if.c h1.c
cat `test -f "if.c" || echo $(VPATH)/`if.c h1.c >$@
Things get worse when your prerequisites are in a macro.
VPATH = ../pkg/src
HEADERS = f.h g.h h.h
install-HEADERS: $(HEADERS)
for i in $(HEADERS); do \
$(INSTALL) -m 644 \
`test -f $$i || echo $(VPATH)/`$$i \
$(DESTDIR)$(includedir)/$$i; \
done
The above `install-HEADERS' rule is not Solaris-proof because `for i
in $(HEADERS);' is expanded to `for i in f.h g.h h.h;' where `f.h' and
`g.h' are plain words and are hence subject to `VPATH' adjustments.
If the three files are in `../pkg/src', the rule is run as:
for i in ../pkg/src/f.h ../pkg/src/g.h h.h; do \
install -m 644 \
`test -f $i || echo ../pkg/src/`$i \
/usr/local/include/$i; \
done
where the two first `install' calls fail. For instance, consider
the `f.h' installation:
install -m 644 \
`test -f ../pkg/src/f.h || \
echo ../pkg/src/ \
`../pkg/src/f.h \
/usr/local/include/../pkg/src/f.h;
It reduces to:
install -m 644 \
../pkg/src/f.h \
/usr/local/include/../pkg/src/f.h;
Note that the manual `VPATH' search did not cause any problems here;
however this command installs `f.h' in an incorrect directory.
Trying to quote `$(HEADERS)' in some way, as we did for `foo.c' a
few makefiles ago, does not help:
install-HEADERS: $(HEADERS)
headers='$(HEADERS)'; \
for i in $$headers; do \
$(INSTALL) -m 644 \
`test -f $$i || echo $(VPATH)/`$$i \
$(DESTDIR)$(includedir)/$$i; \
done
Now, `headers='$(HEADERS)'' macroexpands to:
headers='f.h g.h h.h'
but `g.h' is still a plain word. (As an aside, the idiom
`headers='$(HEADERS)'; for i in $$headers;' is a good idea if
`$(HEADERS)' can be empty, because some shells diagnose a syntax error
on `for i in;'.)
One workaround is to strip this unwanted `../pkg/src/' prefix
manually:
VPATH = ../pkg/src
HEADERS = f.h g.h h.h
install-HEADERS: $(HEADERS)
headers='$(HEADERS)'; \
for i in $$headers; do \
i=`expr "$$i" : '$(VPATH)/\(.*\)'`;
$(INSTALL) -m 644 \
`test -f $$i || echo $(VPATH)/`$$i \
$(DESTDIR)$(includedir)/$$i; \
done
Automake does something similar. However the above hack works only
if the files listed in `HEADERS' are in the current directory or a
subdirectory; they should not be in an enclosing directory. If we had
`HEADERS = ../f.h', the above fragment would fail in a VPATH build with
Tru64 `make'. The reason is that not only does Tru64 `make' rewrite
dependencies, but it also simplifies them. Hence `../f.h' becomes
`../pkg/f.h' instead of `../pkg/src/../f.h'. This obviously defeats
any attempt to strip a leading `../pkg/src/' component.
The following example makes the behavior of Tru64 `make' more
apparent.
$ cat Makefile
VPATH = sub
all: ../foo
echo ../foo
$ ls
Makefile foo
$ make
echo foo
foo
Dependency `../foo' was found in `sub/../foo', but Tru64 `make'
simplified it as `foo'. (Note that the `sub/' directory does not even
exist, this just means that the simplification occurred before the file
was checked for.)
For the record here is how SunOS 4 `make' behaves on this example.
$ make
make: Fatal error: Don't know how to make target `../foo'
$ mkdir sub
$ make
echo sub/../foo
sub/../foo

File: autoconf.info, Node: Tru64 Directory Magic, Next: Make Target Lookup, Prev: Automatic Rule Rewriting, Up: VPATH and Make
11.13.4 Tru64 `make' Creates Prerequisite Directories Magically
---------------------------------------------------------------
When a prerequisite is a subdirectory of `VPATH', Tru64 `make' creates
it in the current directory.
$ mkdir -p foo/bar build
$ cd build
$ cat >Makefile <<END
VPATH = ..
all: foo/bar
END
$ make
mkdir foo
mkdir foo/bar
This can yield unexpected results if a rule uses a manual `VPATH'
search as presented before.
VPATH = ..
all : foo/bar
command `test -d foo/bar || echo ../`foo/bar
The above `command' is run on the empty `foo/bar' directory that was
created in the current directory.

File: autoconf.info, Node: Make Target Lookup, Prev: Tru64 Directory Magic, Up: VPATH and Make
11.13.5 Make Target Lookup
--------------------------
GNU `make' uses a complex algorithm to decide when it should use files
found via a `VPATH' search. *Note How Directory Searches are
Performed: (make)Search Algorithm.
If a target needs to be rebuilt, GNU `make' discards the file name
found during the `VPATH' search for this target, and builds the file
locally using the file name given in the makefile. If a target does
not need to be rebuilt, GNU `make' uses the file name found during the
`VPATH' search.
Other `make' implementations, like NetBSD `make', are easier to
describe: the file name found during the `VPATH' search is used whether
the target needs to be rebuilt or not. Therefore new files are created
locally, but existing files are updated at their `VPATH' location.
OpenBSD and FreeBSD `make', however, never perform a `VPATH' search
for a dependency that has an explicit rule. This is extremely annoying.
When attempting a `VPATH' build for an autoconfiscated package
(e.g., `mkdir build && cd build && ../configure'), this means GNU
`make' builds everything locally in the `build' directory, while BSD
`make' builds new files locally and updates existing files in the
source directory.
$ cat Makefile
VPATH = ..
all: foo.x bar.x
foo.x bar.x: newer.x
@echo Building $@
$ touch ../bar.x
$ touch ../newer.x
$ make # GNU make
Building foo.x
Building bar.x
$ pmake # NetBSD make
Building foo.x
Building ../bar.x
$ fmake # FreeBSD make, OpenBSD make
Building foo.x
Building bar.x
$ tmake # Tru64 make
Building foo.x
Building bar.x
$ touch ../bar.x
$ make # GNU make
Building foo.x
$ pmake # NetBSD make
Building foo.x
$ fmake # FreeBSD make, OpenBSD make
Building foo.x
Building bar.x
$ tmake # Tru64 make
Building foo.x
Building bar.x
Note how NetBSD `make' updates `../bar.x' in its VPATH location, and
how FreeBSD, OpenBSD, and Tru64 `make' always update `bar.x', even when
`../bar.x' is up to date.
Another point worth mentioning is that once GNU `make' has decided
to ignore a `VPATH' file name (e.g., it ignored `../bar.x' in the above
example) it continues to ignore it when the target occurs as a
prerequisite of another rule.
The following example shows that GNU `make' does not look up `bar.x'
in `VPATH' before performing the `.x.y' rule, because it ignored the
`VPATH' result of `bar.x' while running the `bar.x: newer.x' rule.
$ cat Makefile
VPATH = ..
all: bar.y
bar.x: newer.x
@echo Building $@
.SUFFIXES: .x .y
.x.y:
cp $< $@
$ touch ../bar.x
$ touch ../newer.x
$ make # GNU make
Building bar.x
cp bar.x bar.y
cp: cannot stat `bar.x': No such file or directory
make: *** [bar.y] Error 1
$ pmake # NetBSD make
Building ../bar.x
cp ../bar.x bar.y
$ rm bar.y
$ fmake # FreeBSD make, OpenBSD make
echo Building bar.x
cp bar.x bar.y
cp: cannot stat `bar.x': No such file or directory
*** Error code 1
$ tmake # Tru64 make
Building bar.x
cp: bar.x: No such file or directory
*** Exit 1
Note that if you drop away the command from the `bar.x: newer.x'
rule, GNU `make' magically starts to work: it knows that `bar.x' hasn't
been updated, therefore it doesn't discard the result from `VPATH'
(`../bar.x') in succeeding uses. Tru64 also works, but FreeBSD and
OpenBSD still don't.
$ cat Makefile
VPATH = ..
all: bar.y
bar.x: newer.x
.SUFFIXES: .x .y
.x.y:
cp $< $@
$ touch ../bar.x
$ touch ../newer.x
$ make # GNU make
cp ../bar.x bar.y
$ rm bar.y
$ pmake # NetBSD make
cp ../bar.x bar.y
$ rm bar.y
$ fmake # FreeBSD make, OpenBSD make
cp bar.x bar.y
cp: cannot stat `bar.x': No such file or directory
*** Error code 1
$ tmake # Tru64 make
cp ../bar.x bar.y
It seems the sole solution that would please every `make'
implementation is to never rely on `VPATH' searches for targets. In
other words, `VPATH' should be reserved to unbuilt sources.

File: autoconf.info, Node: Single Suffix Rules, Next: Timestamps and Make, Prev: VPATH and Make, Up: Portable Make
11.14 Single Suffix Rules and Separated Dependencies
====================================================
A "Single Suffix Rule" is basically a usual suffix (inference) rule
(`.from.to:'), but which _destination_ suffix is empty (`.from:').
"Separated dependencies" simply refers to listing the prerequisite
of a target, without defining a rule. Usually one can list on the one
hand side, the rules, and on the other hand side, the dependencies.
Solaris `make' does not support separated dependencies for targets
defined by single suffix rules:
$ cat Makefile
.SUFFIXES: .in
foo: foo.in
.in:
cp $< $@
$ touch foo.in
$ make
$ ls
Makefile foo.in
while GNU Make does:
$ gmake
cp foo.in foo
$ ls
Makefile foo foo.in
Note it works without the `foo: foo.in' dependency.
$ cat Makefile
.SUFFIXES: .in
.in:
cp $< $@
$ make foo
cp foo.in foo
and it works with double suffix inference rules:
$ cat Makefile
foo.out: foo.in
.SUFFIXES: .in .out
.in.out:
cp $< $@
$ make
cp foo.in foo.out
As a result, in such a case, you have to write target rules.

File: autoconf.info, Node: Timestamps and Make, Prev: Single Suffix Rules, Up: Portable Make
11.15 Timestamp Resolution and Make
===================================
Traditionally, file timestamps had 1-second resolution, and `make' used
those timestamps to determine whether one file was newer than the
other. However, many modern file systems have timestamps with
1-nanosecond resolution. Some `make' implementations look at the
entire timestamp; others ignore the fractional part, which can lead to
incorrect results. Normally this is not a problem, but in some extreme
cases you may need to use tricks like `sleep 1' to work around
timestamp truncation bugs.
Commands like `cp -p' and `touch -r' typically do not copy file
timestamps to their full resolutions (*note Limitations of Usual
Tools::). Hence you should be wary of rules like this:
dest: src
cp -p src dest
as `dest' often appears to be older than `src' after the timestamp
is truncated, and this can cause `make' to do needless rework the next
time it is invoked. To work around this problem, you can use a
timestamp file, e.g.:
dest-stamp: src
cp -p src dest
date >dest-stamp

File: autoconf.info, Node: Portable C and C++, Next: Manual Configuration, Prev: Portable Make, Up: Top
12 Portable C and C++ Programming
*********************************
C and C++ programs often use low-level features of the underlying
system, and therefore are often more difficult to make portable to other
platforms.
Several standards have been developed to help make your programs more
portable. If you write programs with these standards in mind, you can
have greater confidence that your programs work on a wide variety of
systems. *Note Language Standards Supported by GCC: (gcc)Standards,
for a list of C-related standards. Many programs also assume the Posix
standard (http://www.opengroup.org/susv3).
Some old code is written to be portable to K&R C, which predates any
C standard. K&R C compilers are no longer of practical interest,
though, and the rest of section assumes at least C89, the first C
standard.
Program portability is a huge topic, and this section can only
briefly introduce common pitfalls. *Note Portability between System
Types: (standards)System Portability, for more information.
* Menu:
* Varieties of Unportability:: How to make your programs unportable
* Integer Overflow:: When integers get too large
* Null Pointers:: Properties of null pointers
* Buffer Overruns:: Subscript errors and the like
* Volatile Objects:: `volatile' and signals
* Floating Point Portability:: Portable floating-point arithmetic
* Exiting Portably:: Exiting and the exit status

File: autoconf.info, Node: Varieties of Unportability, Next: Integer Overflow, Up: Portable C and C++
12.1 Varieties of Unportability
===============================
Autoconf tests and ordinary programs often need to test what is allowed
on a system, and therefore they may need to deliberately exceed the
boundaries of what the standards allow, if only to see whether an
optional feature is present. When you write such a program, you should
keep in mind the difference between constraints, unspecified behavior,
and undefined behavior.
In C, a "constraint" is a rule that the compiler must enforce. An
example constraint is that C programs must not declare a bit-field with
negative width. Tests can therefore reliably assume that programs with
negative-width bit-fields are rejected by a compiler that conforms to
the standard.
"Unspecified behavior" is valid behavior, where the standard allows
multiple possibilities. For example, the order of evaluation of
function arguments is unspecified. Some unspecified behavior is
"implementation-defined", i.e., documented by the implementation, but
since Autoconf tests cannot read the documentation they cannot
distinguish between implementation-defined and other unspecified
behavior. It is common for Autoconf tests to probe implementations to
determine otherwise-unspecified behavior.
"Undefined behavior" is invalid behavior, where the standard allows
the implementation to do anything it pleases. For example,
dereferencing a null pointer leads to undefined behavior. If possible,
test programs should avoid undefined behavior, since a program with
undefined behavior might succeed on a test that should fail.
The above rules apply to programs that are intended to conform to the
standard. However, strictly-conforming programs are quite rare, since
the standards are so limiting. A major goal of Autoconf is to support
programs that use implementation features not described by the standard,
and it is fairly common for test programs to violate the above rules, if
the programs work well enough in practice.

File: autoconf.info, Node: Integer Overflow, Next: Null Pointers, Prev: Varieties of Unportability, Up: Portable C and C++
12.2 Integer Overflow
=====================
In C, signed integer overflow leads to undefined behavior. However,
many programs and Autoconf tests assume that signed integer overflow
after addition, subtraction, or multiplication silently wraps around
modulo a power of two, using two's complement arithmetic, so long as
you cast the resulting value to an integer type or store it into an
integer variable. Such programs are portable to the vast majority of
modern platforms. However, signed integer division is not always
harmless: for example, on CPUs of the i386 family, dividing `INT_MIN'
by `-1' yields a SIGFPE signal which by default terminates the program.
Worse, taking the remainder of these two values typically yields the
same signal on these CPUs, even though the C standard requires `INT_MIN
% -1' to yield zero because the expression does not overflow.
GCC users might consider using the `-ftrapv' option if they are
worried about porting their code to the rare platforms where signed
integer overflow does not wrap around after addition, subtraction, or
multiplication.
Unsigned integer overflow reliably wraps around modulo the word size.
This is guaranteed by the C standard and is portable in practice.

File: autoconf.info, Node: Null Pointers, Next: Buffer Overruns, Prev: Integer Overflow, Up: Portable C and C++
12.3 Properties of Null Pointers
================================
Most modern hosts reliably fail when you attempt to dereference a null
pointer.
On almost all modern hosts, null pointers use an all-bits-zero
internal representation, so you can reliably use `memset' with 0 to set
all the pointers in an array to null values.
If `p' is a null pointer to an object type, the C expression `p + 0'
always evaluates to `p' on modern hosts, even though the standard says
that it has undefined behavior.

File: autoconf.info, Node: Buffer Overruns, Next: Volatile Objects, Prev: Null Pointers, Up: Portable C and C++
12.4 Buffer Overruns and Subscript Errors
=========================================
Buffer overruns and subscript errors are the most common dangerous
errors in C programs. They result in undefined behavior because storing
outside an array typically modifies storage that is used by some other
object, and most modern systems lack runtime checks to catch these
errors. Programs should not rely on buffer overruns being caught.
There is one exception to the usual rule that a portable program
cannot address outside an array. In C, it is valid to compute the
address just past an object, e.g., `&a[N]' where `a' has `N' elements,
so long as you do not dereference the resulting pointer. But it is not
valid to compute the address just before an object, e.g., `&a[-1]'; nor
is it valid to compute two past the end, e.g., `&a[N+1]'. On most
platforms `&a[-1] < &a[0] && &a[N] < &a[N+1]', but this is not reliable
in general, and it is usually easy enough to avoid the potential
portability problem, e.g., by allocating an extra unused array element
at the start or end.
Valgrind (http://valgrind.org/) can catch many overruns. GCC users
might also consider using the `-fmudflap' option to catch overruns.
Buffer overruns are usually caused by off-by-one errors, but there
are more subtle ways to get them.
Using `int' values to index into an array or compute array sizes
causes problems on typical 64-bit hosts where an array index might be
2^31 or larger. Index values of type `size_t' avoid this problem, but
cannot be negative. Index values of type `ptrdiff_t' are signed, and
are wide enough in practice.
If you add or multiply two numbers to calculate an array size, e.g.,
`malloc (x * sizeof y + z)', havoc ensues if the addition or
multiplication overflows.
Many implementations of the `alloca' function silently misbehave and
can generate buffer overflows if given sizes that are too large. The
size limits are implementation dependent, but are at least 4000 bytes
on all platforms that we know about.
The standard functions `asctime', `asctime_r', `ctime', `ctime_r',
and `gets' are prone to buffer overflows, and portable code should not
use them unless the inputs are known to be within certain limits. The
time-related functions can overflow their buffers if given timestamps
out of range (e.g., a year less than -999 or greater than 9999).
Time-related buffer overflows cannot happen with recent-enough versions
of the GNU C library, but are possible with other implementations. The
`gets' function is the worst, since it almost invariably overflows its
buffer when presented with an input line larger than the buffer.

File: autoconf.info, Node: Volatile Objects, Next: Floating Point Portability, Prev: Buffer Overruns, Up: Portable C and C++
12.5 Volatile Objects
=====================
The keyword `volatile' is often misunderstood in portable code. Its
use inhibits some memory-access optimizations, but programmers often
wish that it had a different meaning than it actually does.
`volatile' was designed for code that accesses special objects like
memory-mapped device registers whose contents spontaneously change.
Such code is inherently low-level, and it is difficult to specify
portably what `volatile' means in these cases. The C standard says,
"What constitutes an access to an object that has volatile-qualified
type is implementation-defined," so in theory each implementation is
supposed to fill in the gap by documenting what `volatile' means for
that implementation. In practice, though, this documentation is
usually absent or incomplete.
One area of confusion is the distinction between objects defined with
volatile types, and volatile lvalues. From the C standard's point of
view, an object defined with a volatile type has externally visible
behavior. You can think of such objects as having little oscilloscope
probes attached to them, so that the user can observe some properties of
accesses to them, just as the user can observe data written to output
files. However, the standard does not make it clear whether users can
observe accesses by volatile lvalues to ordinary objects. For example:
/* Declare and access a volatile object.
Accesses to X are "visible" to users. */
static int volatile x;
x = 1;
/* Access two ordinary objects via a volatile lvalue.
It's not clear whether accesses to *P are "visible". */
int y;
int *z = malloc (sizeof (int));
int volatile *p;
p = &y;
*p = 1;
p = z;
*p = 1;
Programmers often wish that `volatile' meant "Perform the memory
access here and now, without merging several memory accesses, without
changing the memory word size, and without reordering." But the C
standard does not require this. For objects defined with a volatile
type, accesses must be done before the next sequence point; but
otherwise merging, reordering, and word-size change is allowed. Worse,
it is not clear from the standard whether volatile lvalues provide more
guarantees in general than nonvolatile lvalues, if the underlying
objects are ordinary.
Even when accessing objects defined with a volatile type, the C
standard allows only extremely limited signal handlers: the behavior is
undefined if a signal handler reads any nonlocal object, or writes to
any nonlocal object whose type is not `sig_atomic_t volatile', or calls
any standard library function other than `abort', `signal', and (if C99)
`_Exit'. Hence C compilers need not worry about a signal handler
disturbing ordinary computation, unless the computation accesses a
`sig_atomic_t volatile' lvalue that is not a local variable. (There is
an obscure exception for accesses via a pointer to a volatile
character, since it may point into part of a `sig_atomic_t volatile'
object.) Posix adds to the list of library functions callable from a
portable signal handler, but otherwise is like the C standard in this
area.
Some C implementations allow memory-access optimizations within each
translation unit, such that actual behavior agrees with the behavior
required by the standard only when calling a function in some other
translation unit, and a signal handler acts like it was called from a
different translation unit. The C standard hints that in these
implementations, objects referred to by signal handlers "would require
explicit specification of `volatile' storage, as well as other
implementation-defined restrictions." But unfortunately even for this
special case these other restrictions are often not documented well.
*Note When is a Volatile Object Accessed?: (gcc)Volatiles, for some
restrictions imposed by GCC. *Note Defining Signal Handlers:
(libc)Defining Handlers, for some restrictions imposed by the GNU C
library. Restrictions differ on other platforms.
If possible, it is best to use a signal handler that fits within the
limits imposed by the C and Posix standards.
If this is not practical, you can try the following rules of thumb.
A signal handler should access only volatile lvalues, preferably lvalues
that refer to objects defined with a volatile type, and should not
assume that the accessed objects have an internally consistent state if
they are larger than a machine word. Furthermore, installers should
employ compilers and compiler options that are commonly used for
building operating system kernels, because kernels often need more from
`volatile' than the C Standard requires, and installers who compile an
application in a similar environment can sometimes benefit from the
extra constraints imposed by kernels on compilers. Admittedly we are
handwaving somewhat here, as there are few guarantees in this area; the
rules of thumb may help to fix some bugs but there is a good chance
that they will not fix them all.
For `volatile', C++ has the same problems that C does.
Multithreaded applications have even more problems with `volatile', but
they are beyond the scope of this section.
The bottom line is that using `volatile' typically hurts performance
but should not hurt correctness. In some cases its use does help
correctness, but these cases are often so poorly understood that all
too often adding `volatile' to a data structure merely alleviates some
symptoms of a bug while not fixing the bug in general.

File: autoconf.info, Node: Floating Point Portability, Next: Exiting Portably, Prev: Volatile Objects, Up: Portable C and C++
12.6 Floating Point Portability
===============================
Almost all modern systems use IEEE-754 floating point, and it is safe to
assume IEEE-754 in most portable code these days. For more information,
please see David Goldberg's classic paper What Every Computer Scientist
Should Know About Floating-Point Arithmetic
(http://www.validlab.com/goldberg/paper.pdf).

File: autoconf.info, Node: Exiting Portably, Prev: Floating Point Portability, Up: Portable C and C++
12.7 Exiting Portably
=====================
A C or C++ program can exit with status N by returning N from the
`main' function. Portable programs are supposed to exit either with
status 0 or `EXIT_SUCCESS' to succeed, or with status `EXIT_FAILURE' to
fail, but in practice it is portable to fail by exiting with status 1,
and test programs that assume Posix can fail by exiting with status
values from 1 through 255. Programs on SunOS 2.0 (1985) through 3.5.2
(1988) incorrectly exited with zero status when `main' returned
nonzero, but ancient systems like these are no longer of practical
concern.
A program can also exit with status N by passing N to the `exit'
function, and a program can fail by calling the `abort' function. If a
program is specialized to just some platforms, it can fail by calling
functions specific to those platforms, e.g., `_exit' (Posix) and
`_Exit' (C99). However, like other functions, an exit function should
be declared, typically by including a header. For example, if a C
program calls `exit', it should include `stdlib.h' either directly or
via the default includes (*note Default Includes::).
A program can fail due to undefined behavior such as dereferencing a
null pointer, but this is not recommended as undefined behavior allows
an implementation to do whatever it pleases and this includes exiting
successfully.

File: autoconf.info, Node: Manual Configuration, Next: Site Configuration, Prev: Portable C and C++, Up: Top
13 Manual Configuration
***********************
A few kinds of features can't be guessed automatically by running test
programs. For example, the details of the object-file format, or
special options that need to be passed to the compiler or linker. You
can check for such features using ad-hoc means, such as having
`configure' check the output of the `uname' program, or looking for
libraries that are unique to particular systems. However, Autoconf
provides a uniform method for handling unguessable features.
* Menu:
* Specifying Names:: Specifying the system type
* Canonicalizing:: Getting the canonical system type
* Using System Type:: What to do with the system type

File: autoconf.info, Node: Specifying Names, Next: Canonicalizing, Up: Manual Configuration
13.1 Specifying the System Type
===============================
Like other GNU `configure' scripts, Autoconf-generated `configure'
scripts can make decisions based on a canonical name for the system
type, which has the form: `CPU-VENDOR-OS', where OS can be `SYSTEM' or
`KERNEL-SYSTEM'
`configure' can usually guess the canonical name for the type of
system it's running on. To do so it runs a script called
`config.guess', which infers the name using the `uname' command or
symbols predefined by the C preprocessor.
Alternately, the user can specify the system type with command line
arguments to `configure'. Doing so is necessary when cross-compiling.
In the most complex case of cross-compiling, three system types are
involved. The options to specify them are:
`--build=BUILD-TYPE'
the type of system on which the package is being configured and
compiled. It defaults to the result of running `config.guess'.
`--host=HOST-TYPE'
the type of system on which the package runs. By default it is the
same as the build machine. Specifying it enables the
cross-compilation mode.
`--target=TARGET-TYPE'
the type of system for which any compiler tools in the package
produce code (rarely needed). By default, it is the same as host.
If you mean to override the result of `config.guess', use `--build',
not `--host', since the latter enables cross-compilation. For
historical reasons, passing `--host' also changes the build type.
Therefore, whenever you specify `--host', be sure to specify `--build'
too; this will be fixed in the future. So, to enter cross-compilation
mode, use a command like this
./configure --build=i686-pc-linux-gnu --host=m68k-coff
Note that if you do not specify `--host', `configure' fails if it can't
run the code generated by the specified compiler. For example,
configuring as follows fails:
./configure CC=m68k-coff-gcc
In the future, when cross-compiling Autoconf will _not_ accept tools
(compilers, linkers, assemblers) whose name is not prefixed with the
host type. The only case when this may be useful is when you really
are not cross-compiling, but only building for a
least-common-denominator architecture: an example is building for
`i386-pc-linux-gnu' while running on an `i686-pc-linux-gnu'
architecture. In this case, some particular pairs might be similar
enough to let you get away with the system compilers, but in general
the compiler might make bogus assumptions on the host: if you know what
you are doing, please create symbolic links from the host compiler to
the build compiler.
`configure' recognizes short aliases for many system types; for
example, `decstation' can be used instead of `mips-dec-ultrix4.2'.
`configure' runs a script called `config.sub' to canonicalize system
type aliases.
This section deliberately omits the description of the obsolete
interface; see *Note Hosts and Cross-Compilation::.

File: autoconf.info, Node: Canonicalizing, Next: Using System Type, Prev: Specifying Names, Up: Manual Configuration
13.2 Getting the Canonical System Type
======================================
The following macros make the system type available to `configure'
scripts.
The variables `build_alias', `host_alias', and `target_alias' are
always exactly the arguments of `--build', `--host', and `--target'; in
particular, they are left empty if the user did not use them, even if
the corresponding `AC_CANONICAL' macro was run. Any configure script
may use these variables anywhere. These are the variables that should
be used when in interaction with the user.
If you need to recognize some special environments based on their
system type, run the following macros to get canonical system names.
These variables are not set before the macro call.
If you use these macros, you must distribute `config.guess' and
`config.sub' along with your source code. *Note Output::, for
information about the `AC_CONFIG_AUX_DIR' macro which you can use to
control in which directory `configure' looks for those scripts.
-- Macro: AC_CANONICAL_BUILD
Compute the canonical build-system type variable, `build', and its
three individual parts `build_cpu', `build_vendor', and `build_os'.
If `--build' was specified, then `build' is the canonicalization
of `build_alias' by `config.sub', otherwise it is determined by
the shell script `config.guess'.
-- Macro: AC_CANONICAL_HOST
Compute the canonical host-system type variable, `host', and its
three individual parts `host_cpu', `host_vendor', and `host_os'.
If `--host' was specified, then `host' is the canonicalization of
`host_alias' by `config.sub', otherwise it defaults to `build'.
-- Macro: AC_CANONICAL_TARGET
Compute the canonical target-system type variable, `target', and
its three individual parts `target_cpu', `target_vendor', and
`target_os'.
If `--target' was specified, then `target' is the canonicalization
of `target_alias' by `config.sub', otherwise it defaults to `host'.
Note that there can be artifacts due to the backward compatibility
code. See *Note Hosts and Cross-Compilation::, for more.

File: autoconf.info, Node: Using System Type, Prev: Canonicalizing, Up: Manual Configuration
13.3 Using the System Type
==========================
In `configure.ac' the system type is generally used by one or more
`case' statements to select system-specifics. Shell wildcards can be
used to match a group of system types.
For example, an extra assembler code object file could be chosen,
giving access to a CPU cycle counter register. `$(CYCLE_OBJ)' in the
following would be used in a makefile to add the object to a program or
library.
case $host in
alpha*-*-*) CYCLE_OBJ=rpcc.o ;;
i?86-*-*) CYCLE_OBJ=rdtsc.o ;;
*) CYCLE_OBJ= ;;
esac
AC_SUBST([CYCLE_OBJ])
`AC_CONFIG_LINKS' (*note Configuration Links::) is another good way
to select variant source files, for example optimized code for some
CPUs. The configured CPU type doesn't always indicate exact CPU types,
so some runtime capability checks may be necessary too.
case $host in
alpha*-*-*) AC_CONFIG_LINKS([dither.c:alpha/dither.c]) ;;
powerpc*-*-*) AC_CONFIG_LINKS([dither.c:powerpc/dither.c]) ;;
*-*-*) AC_CONFIG_LINKS([dither.c:generic/dither.c]) ;;
esac
The host system type can also be used to find cross-compilation tools
with `AC_CHECK_TOOL' (*note Generic Programs::).
The above examples all show `$host', since this is where the code is
going to run. Only rarely is it necessary to test `$build' (which is
where the build is being done).
Whenever you're tempted to use `$host' it's worth considering
whether some sort of probe would be better. New system types come along
periodically or previously missing features are added. Well-written
probes can adapt themselves to such things, but hard-coded lists of
names can't. Here are some guidelines,
* Availability of libraries and library functions should always be
checked by probing.
* Variant behavior of system calls is best identified with runtime
tests if possible, but bug workarounds or obscure difficulties
might have to be driven from `$host'.
* Assembler code is inevitably highly CPU-specific and is best
selected according to `$host_cpu'.
* Assembler variations like underscore prefix on globals or ELF
versus COFF type directives are however best determined by
probing, perhaps even examining the compiler output.
`$target' is for use by a package creating a compiler or similar.
For ordinary packages it's meaningless and should not be used. It
indicates what the created compiler should generate code for, if it can
cross-compile. `$target' generally selects various hard-coded CPU and
system conventions, since usually the compiler or tools under
construction themselves determine how the target works.

File: autoconf.info, Node: Site Configuration, Next: Running configure Scripts, Prev: Manual Configuration, Up: Top
14 Site Configuration
*********************
`configure' scripts support several kinds of local configuration
decisions. There are ways for users to specify where external software
packages are, include or exclude optional features, install programs
under modified names, and set default values for `configure' options.
* Menu:
* Help Formatting:: Customizing `configure --help'
* External Software:: Working with other optional software
* Package Options:: Selecting optional features
* Pretty Help Strings:: Formatting help string
* Site Details:: Configuring site details
* Transforming Names:: Changing program names when installing
* Site Defaults:: Giving `configure' local defaults

File: autoconf.info, Node: Help Formatting, Next: External Software, Up: Site Configuration
14.1 Controlling Help Output
============================
Users consult `configure --help' to learn of configuration decisions
specific to your package. By default, `configure' breaks this output
into sections for each type of option; within each section, help
strings appear in the order `configure.ac' defines them:
Optional Features:
...
--enable-bar include bar
Optional Packages:
...
--with-foo use foo
-- Macro: AC_PRESERVE_HELP_ORDER
Request an alternate `--help' format, in which options of all
types appear together, in the order defined. Call this macro
before any `AC_ARG_ENABLE' or `AC_ARG_WITH'.
Optional Features and Packages:
...
--enable-bar include bar
--with-foo use foo

File: autoconf.info, Node: External Software, Next: Package Options, Prev: Help Formatting, Up: Site Configuration
14.2 Working With External Software
===================================
Some packages require, or can optionally use, other software packages
that are already installed. The user can give `configure' command line
options to specify which such external software to use. The options
have one of these forms:
--with-PACKAGE[=ARG]
--without-PACKAGE
For example, `--with-gnu-ld' means work with the GNU linker instead
of some other linker. `--with-x' means work with The X Window System.
The user can give an argument by following the package name with `='
and the argument. Giving an argument of `no' is for packages that are
used by default; it says to _not_ use the package. An argument that is
neither `yes' nor `no' could include a name or number of a version of
the other package, to specify more precisely which other package this
program is supposed to work with. If no argument is given, it defaults
to `yes'. `--without-PACKAGE' is equivalent to `--with-PACKAGE=no'.
`configure' scripts do not complain about `--with-PACKAGE' options
that they do not support. This behavior permits configuring a source
tree containing multiple packages with a top-level `configure' script
when the packages support different options, without spurious error
messages about options that some of the packages support. An
unfortunate side effect is that option spelling errors are not
diagnosed. No better approach to this problem has been suggested so
far.
For each external software package that may be used, `configure.ac'
should call `AC_ARG_WITH' to detect whether the `configure' user asked
to use it. Whether each package is used or not by default, and which
arguments are valid, is up to you.
-- Macro: AC_ARG_WITH (PACKAGE, HELP-STRING, [ACTION-IF-GIVEN],
[ACTION-IF-NOT-GIVEN])
If the user gave `configure' the option `--with-PACKAGE' or
`--without-PACKAGE', run shell commands ACTION-IF-GIVEN. If
neither option was given, run shell commands ACTION-IF-NOT-GIVEN.
The name PACKAGE indicates another software package that this
program should work with. It should consist only of alphanumeric
characters, dashes, and dots.
The option's argument is available to the shell commands
ACTION-IF-GIVEN in the shell variable `withval', which is actually
just the value of the shell variable `with_PACKAGE', with any
non-alphanumeric characters changed into `_'. You may use that
variable instead, if you wish.
The argument HELP-STRING is a description of the option that looks
like this:
--with-readline support fancy command line editing
HELP-STRING may be more than one line long, if more detail is
needed. Just make sure the columns line up in `configure --help'.
Avoid tabs in the help string. You'll need to enclose the help
string in `[' and `]' in order to produce the leading blanks.
You should format your HELP-STRING with the macro `AS_HELP_STRING'
(*note Pretty Help Strings::).
The following example shows how to use the `AC_ARG_WITH' macro in
a common situation. You want to let the user decide whether to
enable support for an external library (e.g., the readline
library); if the user specified neither `--with-readline' nor
`--without-readline', you want to enable support for readline only
if the library is available on the system.
AC_ARG_WITH([readline],
[AS_HELP_STRING([--with-readline],
[support fancy command line editing @<:@default=check@:>@])],
[],
[with_readline=check])
LIBREADLINE=
AS_IF([test "x$with_readline" != xno],
[AC_CHECK_LIB([readline], [main],
[AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"])
AC_DEFINE([HAVE_LIBREADLINE], [1],
[Define if you have libreadline])
],
[if test "x$with_readline" != xcheck; then
AC_MSG_FAILURE(
[--with-readline was given, but test for readline failed])
fi
], -lncurses)])
The next example shows how to use `AC_ARG_WITH' to give the user
the possibility to enable support for the readline library, in
case it is still experimental and not well tested, and is
therefore disabled by default.
AC_ARG_WITH([readline],
[AS_HELP_STRING([--with-readline],
[enable experimental support for readline])],
[],
[with_readline=no])
LIBREADLINE=
AS_IF([test "x$with_readline" != xno],
[AC_CHECK_LIB([readline], [main],
[AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"])
AC_DEFINE([HAVE_LIBREADLINE], [1],
[Define if you have libreadline])
],
[AC_MSG_FAILURE(
[--with-readline was given, but test for readline failed])],
[-lncurses])])
The last example shows how to use `AC_ARG_WITH' to give the user
the possibility to disable support for the readline library, given
that it is an important feature and that it should be enabled by
default.
AC_ARG_WITH([readline],
[AS_HELP_STRING([--without-readline],
[disable support for readline])],
[],
[with_readline=yes])
LIBREADLINE=
AS_IF([test "x$with_readline" != xno],
[AC_CHECK_LIB([readline], [main],
[AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"])
AC_DEFINE([HAVE_LIBREADLINE], [1],
[Define if you have libreadline])
],
[AC_MSG_FAILURE(
[readline test failed (--without-readline to disable)])],
[-lncurses])])
These three examples can be easily adapted to the case where
`AC_ARG_ENABLE' should be preferred to `AC_ARG_WITH' (see *Note
Package Options::).
-- Macro: AC_WITH (PACKAGE, ACTION-IF-GIVEN, [ACTION-IF-NOT-GIVEN])
This is an obsolete version of `AC_ARG_WITH' that does not support
providing a help string.

File: autoconf.info, Node: Package Options, Next: Pretty Help Strings, Prev: External Software, Up: Site Configuration
14.3 Choosing Package Options
=============================
If a software package has optional compile-time features, the user can
give `configure' command line options to specify whether to compile
them. The options have one of these forms:
--enable-FEATURE[=ARG]
--disable-FEATURE
These options allow users to choose which optional features to build
and install. `--enable-FEATURE' options should never make a feature
behave differently or cause one feature to replace another. They
should only cause parts of the program to be built rather than left out.
The user can give an argument by following the feature name with `='
and the argument. Giving an argument of `no' requests that the feature
_not_ be made available. A feature with an argument looks like
`--enable-debug=stabs'. If no argument is given, it defaults to `yes'.
`--disable-FEATURE' is equivalent to `--enable-FEATURE=no'.
`configure' scripts do not complain about `--enable-FEATURE' options
that they do not support. This behavior permits configuring a source
tree containing multiple packages with a top-level `configure' script
when the packages support different options, without spurious error
messages about options that some of the packages support. An
unfortunate side effect is that option spelling errors are not
diagnosed. No better approach to this problem has been suggested so
far.
For each optional feature, `configure.ac' should call
`AC_ARG_ENABLE' to detect whether the `configure' user asked to include
it. Whether each feature is included or not by default, and which
arguments are valid, is up to you.
-- Macro: AC_ARG_ENABLE (FEATURE, HELP-STRING, [ACTION-IF-GIVEN],
[ACTION-IF-NOT-GIVEN])
If the user gave `configure' the option `--enable-FEATURE' or
`--disable-FEATURE', run shell commands ACTION-IF-GIVEN. If
neither option was given, run shell commands ACTION-IF-NOT-GIVEN.
The name FEATURE indicates an optional user-level facility. It
should consist only of alphanumeric characters, dashes, and dots.
The option's argument is available to the shell commands
ACTION-IF-GIVEN in the shell variable `enableval', which is
actually just the value of the shell variable `enable_FEATURE',
with any non-alphanumeric characters changed into `_'. You may
use that variable instead, if you wish. The HELP-STRING argument
is like that of `AC_ARG_WITH' (*note External Software::).
You should format your HELP-STRING with the macro `AS_HELP_STRING'
(*note Pretty Help Strings::).
See the examples suggested with the definition of `AC_ARG_WITH'
(*note External Software::) to get an idea of possible
applications of `AC_ARG_ENABLE'.
-- Macro: AC_ENABLE (FEATURE, ACTION-IF-GIVEN, [ACTION-IF-NOT-GIVEN])
This is an obsolete version of `AC_ARG_ENABLE' that does not
support providing a help string.

File: autoconf.info, Node: Pretty Help Strings, Next: Site Details, Prev: Package Options, Up: Site Configuration
14.4 Making Your Help Strings Look Pretty
=========================================
Properly formatting the `help strings' which are used in `AC_ARG_WITH'
(*note External Software::) and `AC_ARG_ENABLE' (*note Package
Options::) can be challenging. Specifically, you want your own `help
strings' to line up in the appropriate columns of `configure --help'
just like the standard Autoconf `help strings' do. This is the purpose
of the `AS_HELP_STRING' macro.
-- Macro: AS_HELP_STRING (LEFT-HAND-SIDE, RIGHT-HAND-SIDE)
Expands into an help string that looks pretty when the user
executes `configure --help'. It is typically used in `AC_ARG_WITH'
(*note External Software::) or `AC_ARG_ENABLE' (*note Package
Options::). The following example makes this clearer.
AC_ARG_WITH([foo],
[AS_HELP_STRING([--with-foo],
[use foo (default is no)])],
[use_foo=$withval],
[use_foo=no])
The second argument of `AS_HELP_STRING' is not a literal, and
should not be double quoted. *Note Autoconf Language::, for a
more detailed explanation. Then the last few lines of `configure
--help' appear like this:
--enable and --with options recognized:
--with-foo use foo (default is no)
The `AS_HELP_STRING' macro is particularly helpful when the
LEFT-HAND-SIDE and/or RIGHT-HAND-SIDE are composed of macro
arguments, as shown in the following example.
AC_DEFUN([MY_ARG_WITH],
[AC_ARG_WITH([$1],
[AS_HELP_STRING([--with-$1], [use $1 (default is $2)])],
[use_[]$1=$withval],
[use_[]$1=$2])])

File: autoconf.info, Node: Site Details, Next: Transforming Names, Prev: Pretty Help Strings, Up: Site Configuration
14.5 Configuring Site Details
=============================
Some software packages require complex site-specific information. Some
examples are host names to use for certain services, company names, and
email addresses to contact. Since some configuration scripts generated
by Metaconfig ask for such information interactively, people sometimes
wonder how to get that information in Autoconf-generated configuration
scripts, which aren't interactive.
Such site configuration information should be put in a file that is
edited _only by users_, not by programs. The location of the file can
either be based on the `prefix' variable, or be a standard location
such as the user's home directory. It could even be specified by an
environment variable. The programs should examine that file at
runtime, rather than at compile time. Runtime configuration is more
convenient for users and makes the configuration process simpler than
getting the information while configuring. *Note Variables for
Installation Directories: (standards)Directory Variables, for more
information on where to put data files.

File: autoconf.info, Node: Transforming Names, Next: Site Defaults, Prev: Site Details, Up: Site Configuration
14.6 Transforming Program Names When Installing
===============================================
Autoconf supports changing the names of programs when installing them.
In order to use these transformations, `configure.ac' must call the
macro `AC_ARG_PROGRAM'.
-- Macro: AC_ARG_PROGRAM
Place in output variable `program_transform_name' a sequence of
`sed' commands for changing the names of installed programs.
If any of the options described below are given to `configure',
program names are transformed accordingly. Otherwise, if
`AC_CANONICAL_TARGET' has been called and a `--target' value is
given, the target type followed by a dash is used as a prefix.
Otherwise, no program name transformation is done.
* Menu:
* Transformation Options:: `configure' options to transform names
* Transformation Examples:: Sample uses of transforming names
* Transformation Rules:: Makefile uses of transforming names

File: autoconf.info, Node: Transformation Options, Next: Transformation Examples, Up: Transforming Names
14.6.1 Transformation Options
-----------------------------
You can specify name transformations by giving `configure' these
command line options:
`--program-prefix=PREFIX'
prepend PREFIX to the names;
`--program-suffix=SUFFIX'
append SUFFIX to the names;
`--program-transform-name=EXPRESSION'
perform `sed' substitution EXPRESSION on the names.

File: autoconf.info, Node: Transformation Examples, Next: Transformation Rules, Prev: Transformation Options, Up: Transforming Names
14.6.2 Transformation Examples
------------------------------
These transformations are useful with programs that can be part of a
cross-compilation development environment. For example, a
cross-assembler running on a Sun 4 configured with
`--target=i960-vxworks' is normally installed as `i960-vxworks-as',
rather than `as', which could be confused with a native Sun 4 assembler.
You can force a program name to begin with `g', if you don't want
GNU programs installed on your system to shadow other programs with the
same name. For example, if you configure GNU `diff' with
`--program-prefix=g', then when you run `make install' it is installed
as `/usr/local/bin/gdiff'.
As a more sophisticated example, you could use
--program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/'
to prepend `g' to most of the program names in a source tree,
excepting those like `gdb' that already have one and those like `less'
and `lesskey' that aren't GNU programs. (That is assuming that you
have a source tree containing those programs that is set up to use this
feature.)
One way to install multiple versions of some programs simultaneously
is to append a version number to the name of one or both. For example,
if you want to keep Autoconf version 1 around for awhile, you can
configure Autoconf version 2 using `--program-suffix=2' to install the
programs as `/usr/local/bin/autoconf2', `/usr/local/bin/autoheader2',
etc. Nevertheless, pay attention that only the binaries are renamed,
therefore you'd have problems with the library files which might
overlap.

File: autoconf.info, Node: Transformation Rules, Prev: Transformation Examples, Up: Transforming Names
14.6.3 Transformation Rules
---------------------------
Here is how to use the variable `program_transform_name' in a
`Makefile.in':
PROGRAMS = cp ls rm
transform = @program_transform_name@
install:
for p in $(PROGRAMS); do \
$(INSTALL_PROGRAM) $$p $(DESTDIR)$(bindir)/`echo $$p | \
sed '$(transform)'`; \
done
uninstall:
for p in $(PROGRAMS); do \
rm -f $(DESTDIR)$(bindir)/`echo $$p | sed '$(transform)'`; \
done
It is guaranteed that `program_transform_name' is never empty, and
that there are no useless separators. Therefore you may safely embed
`program_transform_name' within a sed program using `;':
transform = @program_transform_name@
transform_exe = s/$(EXEEXT)$$//;$(transform);s/$$/$(EXEEXT)/
Whether to do the transformations on documentation files (Texinfo or
`man') is a tricky question; there seems to be no perfect answer, due
to the several reasons for name transforming. Documentation is not
usually particular to a specific architecture, and Texinfo files do not
conflict with system documentation. But they might conflict with
earlier versions of the same files, and `man' pages sometimes do
conflict with system documentation. As a compromise, it is probably
best to do name transformations on `man' pages but not on Texinfo
manuals.

File: autoconf.info, Node: Site Defaults, Prev: Transforming Names, Up: Site Configuration
14.7 Setting Site Defaults
==========================
Autoconf-generated `configure' scripts allow your site to provide
default values for some configuration values. You do this by creating
site- and system-wide initialization files.
If the environment variable `CONFIG_SITE' is set, `configure' uses
its value as the name of a shell script to read. Otherwise, it reads
the shell script `PREFIX/share/config.site' if it exists, then
`PREFIX/etc/config.site' if it exists. Thus, settings in
machine-specific files override those in machine-independent ones in
case of conflict.
Site files can be arbitrary shell scripts, but only certain kinds of
code are really appropriate to be in them. Because `configure' reads
any cache file after it has read any site files, a site file can define
a default cache file to be shared between all Autoconf-generated
`configure' scripts run on that system (*note Cache Files::). If you
set a default cache file in a site file, it is a good idea to also set
the output variable `CC' in that site file, because the cache file is
only valid for a particular compiler, but many systems have several
available.
You can examine or override the value set by a command line option to
`configure' in a site file; options set shell variables that have the
same names as the options, with any dashes turned into underscores.
The exceptions are that `--without-' and `--disable-' options are like
giving the corresponding `--with-' or `--enable-' option and the value
`no'. Thus, `--cache-file=localcache' sets the variable `cache_file'
to the value `localcache'; `--enable-warnings=no' or
`--disable-warnings' sets the variable `enable_warnings' to the value
`no'; `--prefix=/usr' sets the variable `prefix' to the value `/usr';
etc.
Site files are also good places to set default values for other
output variables, such as `CFLAGS', if you need to give them non-default
values: anything you would normally do, repetitively, on the command
line. If you use non-default values for PREFIX or EXEC_PREFIX
(wherever you locate the site file), you can set them in the site file
if you specify it with the `CONFIG_SITE' environment variable.
You can set some cache values in the site file itself. Doing this is
useful if you are cross-compiling, where it is impossible to check
features that require running a test program. You could "prime the
cache" by setting those values correctly for that system in
`PREFIX/etc/config.site'. To find out the names of the cache variables
you need to set, look for shell variables with `_cv_' in their names in
the affected `configure' scripts, or in the Autoconf M4 source code for
those macros.
The cache file is careful to not override any variables set in the
site files. Similarly, you should not override command-line options in
the site files. Your code should check that variables such as `prefix'
and `cache_file' have their default values (as set near the top of
`configure') before changing them.
Here is a sample file `/usr/share/local/gnu/share/config.site'. The
command `configure --prefix=/usr/share/local/gnu' would read this file
(if `CONFIG_SITE' is not set to a different file).
# config.site for configure
#
# Change some defaults.
test "$prefix" = NONE && prefix=/usr/share/local/gnu
test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu
test "$sharedstatedir" = '$prefix/com' && sharedstatedir=/var
test "$localstatedir" = '$prefix/var' && localstatedir=/var
# Give Autoconf 2.x generated configure scripts a shared default
# cache file for feature test results, architecture-specific.
if test "$cache_file" = /dev/null; then
cache_file="$prefix/var/config.cache"
# A cache file is only valid for one C compiler.
CC=gcc
fi

File: autoconf.info, Node: Running configure Scripts, Next: config.status Invocation, Prev: Site Configuration, Up: Top
15 Running `configure' Scripts
******************************
Below are instructions on how to configure a package that uses a
`configure' script, suitable for inclusion as an `INSTALL' file in the
package. A plain-text version of `INSTALL' which you may use comes
with Autoconf.
* Menu:
* Basic Installation:: Instructions for typical cases
* Compilers and Options:: Selecting compilers and optimization
* Multiple Architectures:: Compiling for multiple architectures at once
* Installation Names:: Installing in different directories
* Optional Features:: Selecting optional features
* System Type:: Specifying the system type
* Sharing Defaults:: Setting site-wide defaults for `configure'
* Defining Variables:: Specifying the compiler etc.
* configure Invocation:: Changing how `configure' runs

File: autoconf.info, Node: Basic Installation, Next: Compilers and Options, Up: Running configure Scripts
15.1 Basic Installation
=======================
Briefly, the shell commands `./configure; make; make install' should
configure, build, and install this package. The following
more-detailed instructions are generic; see the `README' file for
instructions specific to this package.
The `configure' shell script attempts to guess correct values for
various system-dependent variables used during compilation. It uses
those values to create a `Makefile' in each directory of the package.
It may also create one or more `.h' files containing system-dependent
definitions. Finally, it creates a shell script `config.status' that
you can run in the future to recreate the current configuration, and a
file `config.log' containing compiler output (useful mainly for
debugging `configure').
It can also use an optional file (typically called `config.cache'
and enabled with `--cache-file=config.cache' or simply `-C') that saves
the results of its tests to speed up reconfiguring. Caching is
disabled by default to prevent problems with accidental use of stale
cache files.
If you need to do unusual things to compile the package, please try
to figure out how `configure' could check whether to do them, and mail
diffs or instructions to the address given in the `README' so they can
be considered for the next release. If you are using the cache, and at
some point `config.cache' contains results you don't want to keep, you
may remove or edit it.
The file `configure.ac' (or `configure.in') is used to create
`configure' by a program called `autoconf'. You need `configure.ac' if
you want to change it or regenerate `configure' using a newer version
of `autoconf'.
The simplest way to compile this package is:
1. `cd' to the directory containing the package's source code and type
`./configure' to configure the package for your system.
Running `configure' might take a while. While running, it prints
some messages telling which features it is checking for.
2. Type `make' to compile the package.
3. Optionally, type `make check' to run any self-tests that come with
the package.
4. Type `make install' to install the programs and any data files and
documentation.
5. You can remove the program binaries and object files from the
source code directory by typing `make clean'. To also remove the
files that `configure' created (so you can compile the package for
a different kind of computer), type `make distclean'. There is
also a `make maintainer-clean' target, but that is intended mainly
for the package's developers. If you use it, you may have to get
all sorts of other programs in order to regenerate files that came
with the distribution.

File: autoconf.info, Node: Compilers and Options, Next: Multiple Architectures, Prev: Basic Installation, Up: Running configure Scripts
15.2 Compilers and Options
==========================
Some systems require unusual options for compilation or linking that the
`configure' script does not know about. Run `./configure --help' for
details on some of the pertinent environment variables.
You can give `configure' initial values for configuration parameters
by setting variables in the command line or in the environment. Here
is an example:
./configure CC=c99 CFLAGS=-g LIBS=-lposix
*Note Defining Variables::, for more details.

File: autoconf.info, Node: Multiple Architectures, Next: Installation Names, Prev: Compilers and Options, Up: Running configure Scripts
15.3 Compiling For Multiple Architectures
=========================================
You can compile the package for more than one kind of computer at the
same time, by placing the object files for each architecture in their
own directory. To do this, you can use GNU `make'. `cd' to the
directory where you want the object files and executables to go and run
the `configure' script. `configure' automatically checks for the
source code in the directory that `configure' is in and in `..'.
With a non-GNU `make', it is safer to compile the package for one
architecture at a time in the source code directory. After you have
installed the package for one architecture, use `make distclean' before
reconfiguring for another architecture.

File: autoconf.info, Node: Installation Names, Next: Optional Features, Prev: Multiple Architectures, Up: Running configure Scripts
15.4 Installation Names
=======================
By default, `make install' installs the package's commands under
`/usr/local/bin', include files under `/usr/local/include', etc. You
can specify an installation prefix other than `/usr/local' by giving
`configure' the option `--prefix=PREFIX'.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files. If you
pass the option `--exec-prefix=PREFIX' to `configure', the package uses
PREFIX as the prefix for installing programs and libraries.
Documentation and other data files still use the regular prefix.
In addition, if you use an unusual directory layout you can give
options like `--bindir=DIR' to specify different values for particular
kinds of files. Run `configure --help' for a list of the directories
you can set and what kinds of files go in them.
If the package supports it, you can cause programs to be installed
with an extra prefix or suffix on their names by giving `configure' the
option `--program-prefix=PREFIX' or `--program-suffix=SUFFIX'.

File: autoconf.info, Node: Optional Features, Next: System Type, Prev: Installation Names, Up: Running configure Scripts
15.5 Optional Features
======================
Some packages pay attention to `--enable-FEATURE' options to
`configure', where FEATURE indicates an optional part of the package.
They may also pay attention to `--with-PACKAGE' options, where PACKAGE
is something like `gnu-as' or `x' (for the X Window System). The
`README' should mention any `--enable-' and `--with-' options that the
package recognizes.
For packages that use the X Window System, `configure' can usually
find the X include and library files automatically, but if it doesn't,
you can use the `configure' options `--x-includes=DIR' and
`--x-libraries=DIR' to specify their locations.

File: autoconf.info, Node: System Type, Next: Sharing Defaults, Prev: Optional Features, Up: Running configure Scripts
15.6 Specifying the System Type
===============================
There may be some features `configure' cannot figure out automatically,
but needs to determine by the type of machine the package will run on.
Usually, assuming the package is built to be run on the _same_
architectures, `configure' can figure that out, but if it prints a
message saying it cannot guess the machine type, give it the
`--build=TYPE' option. TYPE can either be a short name for the system
type, such as `sun4', or a canonical name which has the form:
CPU-COMPANY-SYSTEM
where SYSTEM can have one of these forms:
OS KERNEL-OS
See the file `config.sub' for the possible values of each field. If
`config.sub' isn't included in this package, then this package doesn't
need to know the machine type.
If you are _building_ compiler tools for cross-compiling, you should
use the option `--target=TYPE' to select the type of system they will
produce code for.
If you want to _use_ a cross compiler, that generates code for a
platform different from the build platform, you should specify the
"host" platform (i.e., that on which the generated programs will
eventually be run) with `--host=TYPE'.

File: autoconf.info, Node: Sharing Defaults, Next: Defining Variables, Prev: System Type, Up: Running configure Scripts
15.7 Sharing Defaults
=====================
If you want to set default values for `configure' scripts to share, you
can create a site shell script called `config.site' that gives default
values for variables like `CC', `cache_file', and `prefix'.
`configure' looks for `PREFIX/share/config.site' if it exists, then
`PREFIX/etc/config.site' if it exists. Or, you can set the
`CONFIG_SITE' environment variable to the location of the site script.
A warning: not all `configure' scripts look for a site script.

File: autoconf.info, Node: Defining Variables, Next: configure Invocation, Prev: Sharing Defaults, Up: Running configure Scripts
15.8 Defining Variables
=======================
Variables not defined in a site shell script can be set in the
environment passed to `configure'. However, some packages may run
configure again during the build, and the customized values of these
variables may be lost. In order to avoid this problem, you should set
them in the `configure' command line, using `VAR=value'. For example:
./configure CC=/usr/local2/bin/gcc
causes the specified `gcc' to be used as the C compiler (unless it is
overridden in the site shell script).
Unfortunately, this technique does not work for `CONFIG_SHELL' due to
an Autoconf bug. Until the bug is fixed you can use this workaround:
CONFIG_SHELL=/bin/bash /bin/bash ./configure CONFIG_SHELL=/bin/bash

File: autoconf.info, Node: configure Invocation, Prev: Defining Variables, Up: Running configure Scripts
15.9 `configure' Invocation
===========================
`configure' recognizes the following options to control how it operates.
`--help'
`-h'
Print a summary of the options to `configure', and exit.
`--version'
`-V'
Print the version of Autoconf used to generate the `configure'
script, and exit.
`--cache-file=FILE'
Enable the cache: use and save the results of the tests in FILE,
traditionally `config.cache'. FILE defaults to `/dev/null' to
disable caching.
`--config-cache'
`-C'
Alias for `--cache-file=config.cache'.
`--quiet'
`--silent'
`-q'
Do not print messages saying which checks are being made. To
suppress all normal output, redirect it to `/dev/null' (any error
messages will still be shown).
`--srcdir=DIR'
Look for the package's source code in directory DIR. Usually
`configure' can determine that directory automatically.
`configure' also accepts some other, not widely useful, options. Run
`configure --help' for more details.

File: autoconf.info, Node: config.status Invocation, Next: Obsolete Constructs, Prev: Running configure Scripts, Up: Top
16 Recreating a Configuration
*****************************
The `configure' script creates a file named `config.status', which
actually configures, "instantiates", the template files. It also
records the configuration options that were specified when the package
was last configured in case reconfiguring is needed.
Synopsis:
./config.status OPTION... [FILE...]
It configures the FILES; if none are specified, all the templates
are instantiated. The files must be specified without their
dependencies, as in
./config.status foobar
not
./config.status foobar:foo.in:bar.in
The supported options are:
`--help'
`-h'
Print a summary of the command line options, the list of the
template files, and exit.
`--version'
`-V'
Print the version number of Autoconf and the configuration
settings, and exit.
`--silent'
`--quiet'
`-q'
Do not print progress messages.
`--debug'
`-d'
Don't remove the temporary files.
`--file=FILE[:TEMPLATE]'
Require that FILE be instantiated as if
`AC_CONFIG_FILES(FILE:TEMPLATE)' was used. Both FILE and TEMPLATE
may be `-' in which case the standard output and/or standard
input, respectively, is used. If a TEMPLATE file name is
relative, it is first looked for in the build tree, and then in
the source tree. *Note Configuration Actions::, for more details.
This option and the following ones provide one way for separately
distributed packages to share the values computed by `configure'.
Doing so can be useful if some of the packages need a superset of
the features that one of them, perhaps a common library, does.
These options allow a `config.status' file to create files other
than the ones that its `configure.ac' specifies, so it can be used
for a different package.
`--header=FILE[:TEMPLATE]'
Same as `--file' above, but with `AC_CONFIG_HEADERS'.
`--recheck'
Ask `config.status' to update itself and exit (no instantiation).
This option is useful if you change `configure', so that the
results of some tests might be different from the previous run.
The `--recheck' option reruns `configure' with the same arguments
you used before, plus the `--no-create' option, which prevents
`configure' from running `config.status' and creating `Makefile'
and other files, and the `--no-recursion' option, which prevents
`configure' from running other `configure' scripts in
subdirectories. (This is so other Make rules can run
`config.status' when it changes; *note Automatic Remaking::, for
an example).
`config.status' checks several optional environment variables that
can alter its behavior:
-- Variable: CONFIG_SHELL
The shell with which to run `configure' for the `--recheck'
option. It must be Bourne-compatible. The default is a shell that
supports `LINENO' if available, and `/bin/sh' otherwise. Invoking
`configure' by hand bypasses this setting, so you may need to use
a command like `CONFIG_SHELL=/bin/bash /bin/bash ./configure' to
insure that the same shell is used everywhere. The absolute name
of the shell should be passed.
-- Variable: CONFIG_STATUS
The file name to use for the shell script that records the
configuration. The default is `./config.status'. This variable is
useful when one package uses parts of another and the `configure'
scripts shouldn't be merged because they are maintained separately.
You can use `./config.status' in your makefiles. For example, in
the dependencies given above (*note Automatic Remaking::),
`config.status' is run twice when `configure.ac' has changed. If that
bothers you, you can make each run only regenerate the files for that
rule:
config.h: stamp-h
stamp-h: config.h.in config.status
./config.status config.h
echo > stamp-h
Makefile: Makefile.in config.status
./config.status Makefile
The calling convention of `config.status' has changed; see *Note
Obsolete config.status Use::, for details.

File: autoconf.info, Node: Obsolete Constructs, Next: Using Autotest, Prev: config.status Invocation, Up: Top
17 Obsolete Constructs
**********************
Autoconf changes, and throughout the years some constructs have been
obsoleted. Most of the changes involve the macros, but in some cases
the tools themselves, or even some concepts, are now considered
obsolete.
You may completely skip this chapter if you are new to Autoconf. Its
intention is mainly to help maintainers updating their packages by
understanding how to move to more modern constructs.
* Menu:
* Obsolete config.status Use:: Different calling convention
* acconfig.h:: Additional entries in `config.h.in'
* autoupdate Invocation:: Automatic update of `configure.ac'
* Obsolete Macros:: Backward compatibility macros
* Autoconf 1:: Tips for upgrading your files
* Autoconf 2.13:: Some fresher tips

File: autoconf.info, Node: Obsolete config.status Use, Next: acconfig.h, Up: Obsolete Constructs
17.1 Obsolete `config.status' Invocation
========================================
`config.status' now supports arguments to specify the files to
instantiate; see *Note config.status Invocation::, for more details.
Before, environment variables had to be used.
-- Variable: CONFIG_COMMANDS
The tags of the commands to execute. The default is the arguments
given to `AC_OUTPUT' and `AC_CONFIG_COMMANDS' in `configure.ac'.
-- Variable: CONFIG_FILES
The files in which to perform `@VARIABLE@' substitutions. The
default is the arguments given to `AC_OUTPUT' and
`AC_CONFIG_FILES' in `configure.ac'.
-- Variable: CONFIG_HEADERS
The files in which to substitute C `#define' statements. The
default is the arguments given to `AC_CONFIG_HEADERS'; if that
macro was not called, `config.status' ignores this variable.
-- Variable: CONFIG_LINKS
The symbolic links to establish. The default is the arguments
given to `AC_CONFIG_LINKS'; if that macro was not called,
`config.status' ignores this variable.
In *Note config.status Invocation::, using this old interface, the
example would be:
config.h: stamp-h
stamp-h: config.h.in config.status
CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_FILES= \
CONFIG_HEADERS=config.h ./config.status
echo > stamp-h
Makefile: Makefile.in config.status
CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_HEADERS= \
CONFIG_FILES=Makefile ./config.status
(If `configure.ac' does not call `AC_CONFIG_HEADERS', there is no need
to set `CONFIG_HEADERS' in the `make' rules. Equally for
`CONFIG_COMMANDS', etc.)

File: autoconf.info, Node: acconfig.h, Next: autoupdate Invocation, Prev: Obsolete config.status Use, Up: Obsolete Constructs
17.2 `acconfig.h'
=================
In order to produce `config.h.in', `autoheader' needs to build or to
find templates for each symbol. Modern releases of Autoconf use
`AH_VERBATIM' and `AH_TEMPLATE' (*note Autoheader Macros::), but in
older releases a file, `acconfig.h', contained the list of needed
templates. `autoheader' copied comments and `#define' and `#undef'
statements from `acconfig.h' in the current directory, if present.
This file used to be mandatory if you `AC_DEFINE' any additional
symbols.
Modern releases of Autoconf also provide `AH_TOP' and `AH_BOTTOM' if
you need to prepend/append some information to `config.h.in'. Ancient
versions of Autoconf had a similar feature: if `./acconfig.h' contains
the string `@TOP@', `autoheader' copies the lines before the line
containing `@TOP@' into the top of the file that it generates.
Similarly, if `./acconfig.h' contains the string `@BOTTOM@',
`autoheader' copies the lines after that line to the end of the file it
generates. Either or both of those strings may be omitted. An even
older alternate way to produce the same effect in ancient versions of
Autoconf is to create the files `FILE.top' (typically `config.h.top')
and/or `FILE.bot' in the current directory. If they exist,
`autoheader' copies them to the beginning and end, respectively, of its
output.
In former versions of Autoconf, the files used in preparing a
software package for distribution were:
configure.ac --. .------> autoconf* -----> configure
+---+
[aclocal.m4] --+ `---.
[acsite.m4] ---' |
+--> [autoheader*] -> [config.h.in]
[acconfig.h] ----. |
+-----'
[config.h.top] --+
[config.h.bot] --'
Using only the `AH_' macros, `configure.ac' should be
self-contained, and should not depend upon `acconfig.h' etc.

File: autoconf.info, Node: autoupdate Invocation, Next: Obsolete Macros, Prev: acconfig.h, Up: Obsolete Constructs
17.3 Using `autoupdate' to Modernize `configure.ac'
===================================================
The `autoupdate' program updates a `configure.ac' file that calls
Autoconf macros by their old names to use the current macro names. In
version 2 of Autoconf, most of the macros were renamed to use a more
uniform and descriptive naming scheme. *Note Macro Names::, for a
description of the new scheme. Although the old names still work
(*note Obsolete Macros::, for a list of the old macros and the
corresponding new names), you can make your `configure.ac' files more
readable and make it easier to use the current Autoconf documentation
if you update them to use the new macro names.
If given no arguments, `autoupdate' updates `configure.ac', backing
up the original version with the suffix `~' (or the value of the
environment variable `SIMPLE_BACKUP_SUFFIX', if that is set). If you
give `autoupdate' an argument, it reads that file instead of
`configure.ac' and writes the updated file to the standard output.
`autoupdate' accepts the following options:
`--help'
`-h'
Print a summary of the command line options and exit.
`--version'
`-V'
Print the version number of Autoconf and exit.
`--verbose'
`-v'
Report processing steps.
`--debug'
`-d'
Don't remove the temporary files.
`--force'
`-f'
Force the update even if the file has not changed. Disregard the
cache.
`--include=DIR'
`-I DIR'
Also look for input files in DIR. Multiple invocations accumulate.
Directories are browsed from last to first.

File: autoconf.info, Node: Obsolete Macros, Next: Autoconf 1, Prev: autoupdate Invocation, Up: Obsolete Constructs
17.4 Obsolete Macros
====================
Several macros are obsoleted in Autoconf, for various reasons (typically
they failed to quote properly, couldn't be extended for more recent
issues, etc.). They are still supported, but deprecated: their use
should be avoided.
During the jump from Autoconf version 1 to version 2, most of the
macros were renamed to use a more uniform and descriptive naming scheme,
but their signature did not change. *Note Macro Names::, for a
description of the new naming scheme. Below, if there is just the
mapping from old names to new names for these macros, the reader is
invited to refer to the definition of the new macro for the signature
and the description.
-- Macro: AC_ALLOCA
`AC_FUNC_ALLOCA'
-- Macro: AC_ARG_ARRAY
removed because of limited usefulness
-- Macro: AC_C_CROSS
This macro is obsolete; it does nothing.
-- Macro: AC_C_LONG_DOUBLE
If the C compiler supports a working `long double' type with more
range or precision than the `double' type, define
`HAVE_LONG_DOUBLE'.
You should use `AC_TYPE_LONG_DOUBLE' or
`AC_TYPE_LONG_DOUBLE_WIDER' instead. *Note Particular Types::.
-- Macro: AC_CANONICAL_SYSTEM
Determine the system type and set output variables to the names of
the canonical system types. *Note Canonicalizing::, for details
about the variables this macro sets.
The user is encouraged to use either `AC_CANONICAL_BUILD', or
`AC_CANONICAL_HOST', or `AC_CANONICAL_TARGET', depending on the
needs. Using `AC_CANONICAL_TARGET' is enough to run the two other
macros.
-- Macro: AC_CHAR_UNSIGNED
`AC_C_CHAR_UNSIGNED'
-- Macro: AC_CHECK_TYPE (TYPE, DEFAULT)
Autoconf, up to 2.13, used to provide this version of
`AC_CHECK_TYPE', deprecated because of its flaws. First, although
it is a member of the `CHECK' clan, it does more than just
checking. Secondly, missing types are defined using `#define',
not `typedef', and this can lead to problems in the case of
pointer types.
This use of `AC_CHECK_TYPE' is obsolete and discouraged; see *Note
Generic Types::, for the description of the current macro.
If the type TYPE is not defined, define it to be the C (or C++)
builtin type DEFAULT, e.g., `short int' or `unsigned int'.
This macro is equivalent to:
AC_CHECK_TYPE([TYPE], [],
[AC_DEFINE_UNQUOTED([TYPE], [DEFAULT],
[Define to `DEFAULT'
if <sys/types.h> does not define.])])
In order to keep backward compatibility, the two versions of
`AC_CHECK_TYPE' are implemented, selected by a simple heuristics:
1. If there are three or four arguments, the modern version is
used.
2. If the second argument appears to be a C or C++ type, then the
obsolete version is used. This happens if the argument is a
C or C++ _builtin_ type or a C identifier ending in `_t',
optionally followed by one of `[(* ' and then by a string of
zero or more characters taken from the set `[]()* _a-zA-Z0-9'.
3. If the second argument is spelled with the alphabet of valid
C and C++ types, the user is warned and the modern version is
used.
4. Otherwise, the modern version is used.
You are encouraged either to use a valid builtin type, or to use
the equivalent modern code (see above), or better yet, to use
`AC_CHECK_TYPES' together with
#ifndef HAVE_LOFF_T
typedef loff_t off_t;
#endif
-- Macro: AC_CHECKING (FEATURE-DESCRIPTION)
Same as `AC_MSG_NOTICE([checking FEATURE-DESCRIPTION...]'.
-- Macro: AC_COMPILE_CHECK (ECHO-TEXT, INCLUDES, FUNCTION-BODY,
ACTION-IF-TRUE, [ACTION-IF-FALSE])
This is an obsolete version of `AC_TRY_COMPILE' itself replaced by
`AC_COMPILE_IFELSE' (*note Running the Compiler::), with the
addition that it prints `checking for ECHO-TEXT' to the standard
output first, if ECHO-TEXT is non-empty. Use `AC_MSG_CHECKING'
and `AC_MSG_RESULT' instead to print messages (*note Printing
Messages::).
-- Macro: AC_CONST
`AC_C_CONST'
-- Macro: AC_CROSS_CHECK
Same as `AC_C_CROSS', which is obsolete too, and does nothing
`:-)'.
-- Macro: AC_CYGWIN
Check for the Cygwin environment in which case the shell variable
`CYGWIN' is set to `yes'. Don't use this macro, the dignified
means to check the nature of the host is using
`AC_CANONICAL_HOST'. As a matter of fact this macro is defined as:
AC_REQUIRE([AC_CANONICAL_HOST])[]dnl
case $host_os in
*cygwin* ) CYGWIN=yes;;
* ) CYGWIN=no;;
esac
Beware that the variable `CYGWIN' has a special meaning when
running Cygwin, and should not be changed. That's yet another
reason not to use this macro.
-- Macro: AC_DECL_SYS_SIGLIST
Same as:
AC_CHECK_DECLS([sys_siglist], [], [],
[#include <signal.h>
/* NetBSD declares sys_siglist in unistd.h. */
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif
])
-- Macro: AC_DECL_YYTEXT
Does nothing, now integrated in `AC_PROG_LEX'.
-- Macro: AC_DIR_HEADER
Like calling `AC_FUNC_CLOSEDIR_VOID' and`AC_HEADER_DIRENT', but
defines a different set of C preprocessor macros to indicate which
header file is found:
Header Old Symbol New Symbol
`dirent.h' `DIRENT' `HAVE_DIRENT_H'
`sys/ndir.h' `SYSNDIR' `HAVE_SYS_NDIR_H'
`sys/dir.h' `SYSDIR' `HAVE_SYS_DIR_H'
`ndir.h' `NDIR' `HAVE_NDIR_H'
-- Macro: AC_DYNIX_SEQ
If on DYNIX/ptx, add `-lseq' to output variable `LIBS'. This
macro used to be defined as
AC_CHECK_LIB([seq], [getmntent], [LIBS="-lseq $LIBS"])
now it is just `AC_FUNC_GETMNTENT'.
-- Macro: AC_EXEEXT
Defined the output variable `EXEEXT' based on the output of the
compiler, which is now done automatically. Typically set to empty
string if Posix and `.exe' if a DOS variant.
-- Macro: AC_EMXOS2
Similar to `AC_CYGWIN' but checks for the EMX environment on OS/2
and sets `EMXOS2'.
-- Macro: AC_ERROR
`AC_MSG_ERROR'
-- Macro: AC_FIND_X
`AC_PATH_X'
-- Macro: AC_FIND_XTRA
`AC_PATH_XTRA'
-- Macro: AC_FOREACH
`m4_foreach_w'
-- Macro: AC_FUNC_CHECK
`AC_CHECK_FUNC'
-- Macro: AC_FUNC_WAIT3
If `wait3' is found and fills in the contents of its third argument
(a `struct rusage *'), which HP-UX does not do, define
`HAVE_WAIT3'.
These days portable programs should use `waitpid', not `wait3', as
`wait3' has been removed from Posix.
-- Macro: AC_GCC_TRADITIONAL
`AC_PROG_GCC_TRADITIONAL'
-- Macro: AC_GETGROUPS_T
`AC_TYPE_GETGROUPS'
-- Macro: AC_GETLOADAVG
`AC_FUNC_GETLOADAVG'
-- Macro: AC_HAVE_FUNCS
`AC_CHECK_FUNCS'
-- Macro: AC_HAVE_HEADERS
`AC_CHECK_HEADERS'
-- Macro: AC_HAVE_LIBRARY (LIBRARY, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES])
This macro is equivalent to calling `AC_CHECK_LIB' with a FUNCTION
argument of `main'. In addition, LIBRARY can be written as any of
`foo', `-lfoo', or `libfoo.a'. In all of those cases, the
compiler is passed `-lfoo'. However, LIBRARY cannot be a shell
variable; it must be a literal name.
-- Macro: AC_HAVE_POUNDBANG
`AC_SYS_INTERPRETER' (different calling convention)
-- Macro: AC_HEADER_CHECK
`AC_CHECK_HEADER'
-- Macro: AC_HEADER_EGREP
`AC_EGREP_HEADER'
-- Macro: AC_HELP_STRING
`AS_HELP_STRING'
-- Macro: AC_INIT (UNIQUE-FILE-IN-SOURCE-DIR)
Formerly `AC_INIT' used to have a single argument, and was
equivalent to:
AC_INIT
AC_CONFIG_SRCDIR(UNIQUE-FILE-IN-SOURCE-DIR)
-- Macro: AC_INLINE
`AC_C_INLINE'
-- Macro: AC_INT_16_BITS
If the C type `int' is 16 bits wide, define `INT_16_BITS'. Use
`AC_CHECK_SIZEOF(int)' instead.
-- Macro: AC_IRIX_SUN
If on IRIX (Silicon Graphics Unix), add `-lsun' to output `LIBS'.
If you were using it to get `getmntent', use `AC_FUNC_GETMNTENT'
instead. If you used it for the NIS versions of the password and
group functions, use `AC_CHECK_LIB(sun, getpwnam)'. Up to
Autoconf 2.13, it used to be
AC_CHECK_LIB([sun], [getmntent], [LIBS="-lsun $LIBS"])
now it is defined as
AC_FUNC_GETMNTENT
AC_CHECK_LIB([sun], [getpwnam])
-- Macro: AC_LANG_C
Same as `AC_LANG([C])'.
-- Macro: AC_LANG_CPLUSPLUS
Same as `AC_LANG([C++])'.
-- Macro: AC_LANG_FORTRAN77
Same as `AC_LANG([Fortran 77])'.
-- Macro: AC_LANG_RESTORE
Select the LANGUAGE that is saved on the top of the stack, as set
by `AC_LANG_SAVE', remove it from the stack, and call
`AC_LANG(LANGUAGE)'.
-- Macro: AC_LANG_SAVE
Remember the current language (as set by `AC_LANG') on a stack.
The current language does not change. `AC_LANG_PUSH' is preferred.
-- Macro: AC_LINK_FILES (SOURCE..., DEST...)
This is an obsolete version of `AC_CONFIG_LINKS'. An updated
version of:
AC_LINK_FILES(config/$machine.h config/$obj_format.h,
host.h object.h)
is:
AC_CONFIG_LINKS([host.h:config/$machine.h
object.h:config/$obj_format.h])
-- Macro: AC_LN_S
`AC_PROG_LN_S'
-- Macro: AC_LONG_64_BITS
Define `LONG_64_BITS' if the C type `long int' is 64 bits wide.
Use the generic macro `AC_CHECK_SIZEOF([long int])' instead.
-- Macro: AC_LONG_DOUBLE
If the C compiler supports a working `long double' type with more
range or precision than the `double' type, define
`HAVE_LONG_DOUBLE'.
You should use `AC_TYPE_LONG_DOUBLE' or
`AC_TYPE_LONG_DOUBLE_WIDER' instead. *Note Particular Types::.
-- Macro: AC_LONG_FILE_NAMES
`AC_SYS_LONG_FILE_NAMES'
-- Macro: AC_MAJOR_HEADER
`AC_HEADER_MAJOR'
-- Macro: AC_MEMORY_H
Used to define `NEED_MEMORY_H' if the `mem' functions were defined
in `memory.h'. Today it is equivalent to
`AC_CHECK_HEADERS([memory.h])'. Adjust your code to depend upon
`HAVE_MEMORY_H', not `NEED_MEMORY_H'; see *Note Standard Symbols::.
-- Macro: AC_MINGW32
Similar to `AC_CYGWIN' but checks for the MinGW compiler
environment and sets `MINGW32'.
-- Macro: AC_MINUS_C_MINUS_O
`AC_PROG_CC_C_O'
-- Macro: AC_MMAP
`AC_FUNC_MMAP'
-- Macro: AC_MODE_T
`AC_TYPE_MODE_T'
-- Macro: AC_OBJEXT
Defined the output variable `OBJEXT' based on the output of the
compiler, after .c files have been excluded. Typically set to `o'
if Posix, `obj' if a DOS variant. Now the compiler checking
macros handle this automatically.
-- Macro: AC_OBSOLETE (THIS-MACRO-NAME, [SUGGESTION])
Make M4 print a message to the standard error output warning that
THIS-MACRO-NAME is obsolete, and giving the file and line number
where it was called. THIS-MACRO-NAME should be the name of the
macro that is calling `AC_OBSOLETE'. If SUGGESTION is given, it
is printed at the end of the warning message; for example, it can
be a suggestion for what to use instead of THIS-MACRO-NAME.
For instance
AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl
You are encouraged to use `AU_DEFUN' instead, since it gives better
services to the user.
-- Macro: AC_OFF_T
`AC_TYPE_OFF_T'
-- Macro: AC_OUTPUT ([FILE]..., [EXTRA-CMDS], [INIT-CMDS])
The use of `AC_OUTPUT' with argument is deprecated. This obsoleted
interface is equivalent to:
AC_CONFIG_FILES(FILE...)
AC_CONFIG_COMMANDS([default],
EXTRA-CMDS, INIT-CMDS)
AC_OUTPUT
-- Macro: AC_OUTPUT_COMMANDS (EXTRA-CMDS, [INIT-CMDS])
Specify additional shell commands to run at the end of
`config.status', and shell commands to initialize any variables
from `configure'. This macro may be called multiple times. It is
obsolete, replaced by `AC_CONFIG_COMMANDS'.
Here is an unrealistic example:
fubar=27
AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.],
[fubar=$fubar])
AC_OUTPUT_COMMANDS([echo this is another, extra, bit],
[echo init bit])
Aside from the fact that `AC_CONFIG_COMMANDS' requires an
additional key, an important difference is that
`AC_OUTPUT_COMMANDS' is quoting its arguments twice, unlike
`AC_CONFIG_COMMANDS'. This means that `AC_CONFIG_COMMANDS' can
safely be given macro calls as arguments:
AC_CONFIG_COMMANDS(foo, [my_FOO()])
Conversely, where one level of quoting was enough for literal
strings with `AC_OUTPUT_COMMANDS', you need two with
`AC_CONFIG_COMMANDS'. The following lines are equivalent:
AC_OUTPUT_COMMANDS([echo "Square brackets: []"])
AC_CONFIG_COMMANDS([default], [[echo "Square brackets: []"]])
-- Macro: AC_PID_T
`AC_TYPE_PID_T'
-- Macro: AC_PREFIX
`AC_PREFIX_PROGRAM'
-- Macro: AC_PROGRAMS_CHECK
`AC_CHECK_PROGS'
-- Macro: AC_PROGRAMS_PATH
`AC_PATH_PROGS'
-- Macro: AC_PROGRAM_CHECK
`AC_CHECK_PROG'
-- Macro: AC_PROGRAM_EGREP
`AC_EGREP_CPP'
-- Macro: AC_PROGRAM_PATH
`AC_PATH_PROG'
-- Macro: AC_REMOTE_TAPE
removed because of limited usefulness
-- Macro: AC_RESTARTABLE_SYSCALLS
`AC_SYS_RESTARTABLE_SYSCALLS'
-- Macro: AC_RETSIGTYPE
`AC_TYPE_SIGNAL'
-- Macro: AC_RSH
removed because of limited usefulness
-- Macro: AC_SCO_INTL
If on SCO Unix, add `-lintl' to output variable `LIBS'. This
macro used to do this:
AC_CHECK_LIB([intl], [strftime], [LIBS="-lintl $LIBS"])
Now it just calls `AC_FUNC_STRFTIME' instead.
-- Macro: AC_SETVBUF_REVERSED
`AC_FUNC_SETVBUF_REVERSED'
-- Macro: AC_SET_MAKE
`AC_PROG_MAKE_SET'
-- Macro: AC_SIZEOF_TYPE
`AC_CHECK_SIZEOF'
-- Macro: AC_SIZE_T
`AC_TYPE_SIZE_T'
-- Macro: AC_STAT_MACROS_BROKEN
`AC_HEADER_STAT'
-- Macro: AC_STDC_HEADERS
`AC_HEADER_STDC'
-- Macro: AC_STRCOLL
`AC_FUNC_STRCOLL'
-- Macro: AC_ST_BLKSIZE
`AC_CHECK_MEMBERS'
-- Macro: AC_ST_BLOCKS
`AC_STRUCT_ST_BLOCKS'
-- Macro: AC_ST_RDEV
`AC_CHECK_MEMBERS'
-- Macro: AC_SYS_RESTARTABLE_SYSCALLS
If the system automatically restarts a system call that is
interrupted by a signal, define `HAVE_RESTARTABLE_SYSCALLS'. This
macro does not check whether system calls are restarted in
general--it checks whether a signal handler installed with
`signal' (but not `sigaction') causes system calls to be
restarted. It does not check whether system calls can be
restarted when interrupted by signals that have no handler.
These days portable programs should use `sigaction' with
`SA_RESTART' if they want restartable system calls. They should
not rely on `HAVE_RESTARTABLE_SYSCALLS', since nowadays whether a
system call is restartable is a dynamic issue, not a
configuration-time issue.
-- Macro: AC_SYS_SIGLIST_DECLARED
`AC_DECL_SYS_SIGLIST'
-- Macro: AC_TEST_CPP
`AC_TRY_CPP', replaced by `AC_PREPROC_IFELSE'.
-- Macro: AC_TEST_PROGRAM
`AC_TRY_RUN', replaced by `AC_RUN_IFELSE'.
-- Macro: AC_TIMEZONE
`AC_STRUCT_TIMEZONE'
-- Macro: AC_TIME_WITH_SYS_TIME
`AC_HEADER_TIME'
-- Macro: AC_TRY_COMPILE (INCLUDES, FUNCTION-BODY, [ACTION-IF-TRUE],
[ACTION-IF-FALSE])
Same as:
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[INCLUDES]],
[[FUNCTION-BODY]])],
[ACTION-IF-TRUE],
[ACTION-IF-FALSE])
*Note Running the Compiler::.
This macro double quotes both INCLUDES and FUNCTION-BODY.
For C and C++, INCLUDES is any `#include' statements needed by the
code in FUNCTION-BODY (INCLUDES is ignored if the currently
selected language is Fortran or Fortran 77). The compiler and
compilation flags are determined by the current language (*note
Language Choice::).
-- Macro: AC_TRY_CPP (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
Same as:
AC_PREPROC_IFELSE(
[AC_LANG_SOURCE([[INPUT]])],
[ACTION-IF-TRUE],
[ACTION-IF-FALSE])
*Note Running the Preprocessor::.
This macro double quotes the INPUT.
-- Macro: AC_TRY_LINK (INCLUDES, FUNCTION-BODY, [ACTION-IF-TRUE],
[ACTION-IF-FALSE])
Same as:
AC_LINK_IFELSE(
[AC_LANG_PROGRAM([[INCLUDES]],
[[FUNCTION-BODY]])],
[ACTION-IF-TRUE],
[ACTION-IF-FALSE])
*Note Running the Compiler::.
This macro double quotes both INCLUDES and FUNCTION-BODY.
Depending on the current language (*note Language Choice::),
create a test program to see whether a function whose body
consists of FUNCTION-BODY can be compiled and linked. If the file
compiles and links successfully, run shell commands
ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND.
This macro double quotes both INCLUDES and FUNCTION-BODY.
For C and C++, INCLUDES is any `#include' statements needed by the
code in FUNCTION-BODY (INCLUDES is ignored if the currently
selected language is Fortran or Fortran 77). The compiler and
compilation flags are determined by the current language (*note
Language Choice::), and in addition `LDFLAGS' and `LIBS' are used
for linking.
-- Macro: AC_TRY_LINK_FUNC (FUNCTION, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
This macro is equivalent to `AC_LINK_IFELSE([AC_LANG_CALL([],
[FUNCTION])], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])'.
-- Macro: AC_TRY_RUN (PROGRAM, [ACTION-IF-TRUE], [ACTION-IF-FALSE],
[ACTION-IF-CROSS-COMPILING])
Same as:
AC_RUN_IFELSE(
[AC_LANG_SOURCE([[PROGRAM]])],
[ACTION-IF-TRUE],
[ACTION-IF-FALSE],
[ACTION-IF-CROSS-COMPILING])
*Note Runtime::.
-- Macro: AC_UID_T
`AC_TYPE_UID_T'
-- Macro: AC_UNISTD_H
Same as `AC_CHECK_HEADERS([unistd.h])'.
-- Macro: AC_USG
Define `USG' if the BSD string functions are defined in
`strings.h'. You should no longer depend upon `USG', but on
`HAVE_STRING_H'; see *Note Standard Symbols::.
-- Macro: AC_UTIME_NULL
`AC_FUNC_UTIME_NULL'
-- Macro: AC_VALIDATE_CACHED_SYSTEM_TUPLE ([CMD])
If the cache file is inconsistent with the current host, target and
build system types, it used to execute CMD or print a default
error message. This is now handled by default.
-- Macro: AC_VERBOSE (RESULT-DESCRIPTION)
`AC_MSG_RESULT'.
-- Macro: AC_VFORK
`AC_FUNC_VFORK'
-- Macro: AC_VPRINTF
`AC_FUNC_VPRINTF'
-- Macro: AC_WAIT3
`AC_FUNC_WAIT3'
-- Macro: AC_WARN
`AC_MSG_WARN'
-- Macro: AC_WORDS_BIGENDIAN
`AC_C_BIGENDIAN'
-- Macro: AC_XENIX_DIR
This macro used to add `-lx' to output variable `LIBS' if on
Xenix. Also, if `dirent.h' is being checked for, added `-ldir' to
`LIBS'. Now it is merely an alias of `AC_HEADER_DIRENT' instead,
plus some code to detect whether running XENIX on which you should
not depend:
AC_MSG_CHECKING([for Xenix])
AC_EGREP_CPP([yes],
[#if defined M_XENIX && !defined M_UNIX
yes
#endif],
[AC_MSG_RESULT([yes]); XENIX=yes],
[AC_MSG_RESULT([no]); XENIX=])
-- Macro: AC_YYTEXT_POINTER
`AC_DECL_YYTEXT'

File: autoconf.info, Node: Autoconf 1, Next: Autoconf 2.13, Prev: Obsolete Macros, Up: Obsolete Constructs
17.5 Upgrading From Version 1
=============================
Autoconf version 2 is mostly backward compatible with version 1.
However, it introduces better ways to do some things, and doesn't
support some of the ugly things in version 1. So, depending on how
sophisticated your `configure.ac' files are, you might have to do some
manual work in order to upgrade to version 2. This chapter points out
some problems to watch for when upgrading. Also, perhaps your
`configure' scripts could benefit from some of the new features in
version 2; the changes are summarized in the file `NEWS' in the
Autoconf distribution.
* Menu:
* Changed File Names:: Files you might rename
* Changed Makefiles:: New things to put in `Makefile.in'
* Changed Macros:: Macro calls you might replace
* Changed Results:: Changes in how to check test results
* Changed Macro Writing:: Better ways to write your own macros

File: autoconf.info, Node: Changed File Names, Next: Changed Makefiles, Up: Autoconf 1
17.5.1 Changed File Names
-------------------------
If you have an `aclocal.m4' installed with Autoconf (as opposed to in a
particular package's source directory), you must rename it to
`acsite.m4'. *Note autoconf Invocation::.
If you distribute `install.sh' with your package, rename it to
`install-sh' so `make' builtin rules don't inadvertently create a file
called `install' from it. `AC_PROG_INSTALL' looks for the script under
both names, but it is best to use the new name.
If you were using `config.h.top', `config.h.bot', or `acconfig.h',
you still can, but you have less clutter if you use the `AH_' macros.
*Note Autoheader Macros::.

File: autoconf.info, Node: Changed Makefiles, Next: Changed Macros, Prev: Changed File Names, Up: Autoconf 1
17.5.2 Changed Makefiles
------------------------
Add `@CFLAGS@', `@CPPFLAGS@', and `@LDFLAGS@' in your `Makefile.in'
files, so they can take advantage of the values of those variables in
the environment when `configure' is run. Doing this isn't necessary,
but it's a convenience for users.
Also add `@configure_input@' in a comment to each input file for
`AC_OUTPUT', so that the output files contain a comment saying they
were produced by `configure'. Automatically selecting the right
comment syntax for all the kinds of files that people call `AC_OUTPUT'
on became too much work.
Add `config.log' and `config.cache' to the list of files you remove
in `distclean' targets.
If you have the following in `Makefile.in':
prefix = /usr/local
exec_prefix = $(prefix)
you must change it to:
prefix = @prefix@
exec_prefix = @exec_prefix@
The old behavior of replacing those variables without `@' characters
around them has been removed.

File: autoconf.info, Node: Changed Macros, Next: Changed Results, Prev: Changed Makefiles, Up: Autoconf 1
17.5.3 Changed Macros
---------------------
Many of the macros were renamed in Autoconf version 2. You can still
use the old names, but the new ones are clearer, and it's easier to find
the documentation for them. *Note Obsolete Macros::, for a table
showing the new names for the old macros. Use the `autoupdate' program
to convert your `configure.ac' to using the new macro names. *Note
autoupdate Invocation::.
Some macros have been superseded by similar ones that do the job
better, but are not call-compatible. If you get warnings about calling
obsolete macros while running `autoconf', you may safely ignore them,
but your `configure' script generally works better if you follow the
advice that is printed about what to replace the obsolete macros with.
In particular, the mechanism for reporting the results of tests has
changed. If you were using `echo' or `AC_VERBOSE' (perhaps via
`AC_COMPILE_CHECK'), your `configure' script's output looks better if
you switch to `AC_MSG_CHECKING' and `AC_MSG_RESULT'. *Note Printing
Messages::. Those macros work best in conjunction with cache
variables. *Note Caching Results::.

File: autoconf.info, Node: Changed Results, Next: Changed Macro Writing, Prev: Changed Macros, Up: Autoconf 1
17.5.4 Changed Results
----------------------
If you were checking the results of previous tests by examining the
shell variable `DEFS', you need to switch to checking the values of the
cache variables for those tests. `DEFS' no longer exists while
`configure' is running; it is only created when generating output
files. This difference from version 1 is because properly quoting the
contents of that variable turned out to be too cumbersome and
inefficient to do every time `AC_DEFINE' is called. *Note Cache
Variable Names::.
For example, here is a `configure.ac' fragment written for Autoconf
version 1:
AC_HAVE_FUNCS(syslog)
case "$DEFS" in
*-DHAVE_SYSLOG*) ;;
*) # syslog is not in the default libraries. See if it's in some other.
saved_LIBS="$LIBS"
for lib in bsd socket inet; do
AC_CHECKING(for syslog in -l$lib)
LIBS="-l$lib $saved_LIBS"
AC_HAVE_FUNCS(syslog)
case "$DEFS" in
*-DHAVE_SYSLOG*) break ;;
*) ;;
esac
LIBS="$saved_LIBS"
done ;;
esac
Here is a way to write it for version 2:
AC_CHECK_FUNCS([syslog])
if test $ac_cv_func_syslog = no; then
# syslog is not in the default libraries. See if it's in some other.
for lib in bsd socket inet; do
AC_CHECK_LIB([$lib], [syslog], [AC_DEFINE([HAVE_SYSLOG])
LIBS="-l$lib $LIBS"; break])
done
fi
If you were working around bugs in `AC_DEFINE_UNQUOTED' by adding
backslashes before quotes, you need to remove them. It now works
predictably, and does not treat quotes (except back quotes) specially.
*Note Setting Output Variables::.
All of the Boolean shell variables set by Autoconf macros now use
`yes' for the true value. Most of them use `no' for false, though for
backward compatibility some use the empty string instead. If you were
relying on a shell variable being set to something like 1 or `t' for
true, you need to change your tests.

File: autoconf.info, Node: Changed Macro Writing, Prev: Changed Results, Up: Autoconf 1
17.5.5 Changed Macro Writing
----------------------------
When defining your own macros, you should now use `AC_DEFUN' instead of
`define'. `AC_DEFUN' automatically calls `AC_PROVIDE' and ensures that
macros called via `AC_REQUIRE' do not interrupt other macros, to
prevent nested `checking...' messages on the screen. There's no actual
harm in continuing to use the older way, but it's less convenient and
attractive. *Note Macro Definitions::.
You probably looked at the macros that came with Autoconf as a guide
for how to do things. It would be a good idea to take a look at the new
versions of them, as the style is somewhat improved and they take
advantage of some new features.
If you were doing tricky things with undocumented Autoconf internals
(macros, variables, diversions), check whether you need to change
anything to account for changes that have been made. Perhaps you can
even use an officially supported technique in version 2 instead of
kludging. Or perhaps not.
To speed up your locally written feature tests, add caching to them.
See whether any of your tests are of general enough usefulness to
encapsulate them into macros that you can share.

File: autoconf.info, Node: Autoconf 2.13, Prev: Autoconf 1, Up: Obsolete Constructs
17.6 Upgrading From Version 2.13
================================
The introduction of the previous section (*note Autoconf 1::) perfectly
suits this section....
Autoconf version 2.50 is mostly backward compatible with version
2.13. However, it introduces better ways to do some things, and
doesn't support some of the ugly things in version 2.13. So,
depending on how sophisticated your `configure.ac' files are, you
might have to do some manual work in order to upgrade to version
2.50. This chapter points out some problems to watch for when
upgrading. Also, perhaps your `configure' scripts could benefit
from some of the new features in version 2.50; the changes are
summarized in the file `NEWS' in the Autoconf distribution.
* Menu:
* Changed Quotation:: Broken code which used to work
* New Macros:: Interaction with foreign macros
* Hosts and Cross-Compilation:: Bugward compatibility kludges
* AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token
* AC_FOO_IFELSE vs AC_TRY_FOO:: A more generic scheme for testing sources

File: autoconf.info, Node: Changed Quotation, Next: New Macros, Up: Autoconf 2.13
17.6.1 Changed Quotation
------------------------
The most important changes are invisible to you: the implementation of
most macros have completely changed. This allowed more factorization of
the code, better error messages, a higher uniformity of the user's
interface etc. Unfortunately, as a side effect, some construct which
used to (miraculously) work might break starting with Autoconf 2.50.
The most common culprit is bad quotation.
For instance, in the following example, the message is not properly
quoted:
AC_INIT
AC_CHECK_HEADERS(foo.h, ,
AC_MSG_ERROR(cannot find foo.h, bailing out))
AC_OUTPUT
Autoconf 2.13 simply ignores it:
$ autoconf-2.13; ./configure --silent
creating cache ./config.cache
configure: error: cannot find foo.h
$
while Autoconf 2.50 produces a broken `configure':
$ autoconf-2.50; ./configure --silent
configure: error: cannot find foo.h
./configure: exit: bad non-numeric arg `bailing'
./configure: exit: bad non-numeric arg `bailing'
$
The message needs to be quoted, and the `AC_MSG_ERROR' invocation
too!
AC_INIT([Example], [1.0], [bug-example@example.org])
AC_CHECK_HEADERS([foo.h], [],
[AC_MSG_ERROR([cannot find foo.h, bailing out])])
AC_OUTPUT
Many many (and many more) Autoconf macros were lacking proper
quotation, including no less than... `AC_DEFUN' itself!
$ cat configure.in
AC_DEFUN([AC_PROG_INSTALL],
[# My own much better version
])
AC_INIT
AC_PROG_INSTALL
AC_OUTPUT
$ autoconf-2.13
autoconf: Undefined macros:
***BUG in Autoconf--please report*** AC_FD_MSG
***BUG in Autoconf--please report*** AC_EPI
configure.in:1:AC_DEFUN([AC_PROG_INSTALL],
configure.in:5:AC_PROG_INSTALL
$ autoconf-2.50
$

File: autoconf.info, Node: New Macros, Next: Hosts and Cross-Compilation, Prev: Changed Quotation, Up: Autoconf 2.13
17.6.2 New Macros
-----------------
While Autoconf was relatively dormant in the late 1990s, Automake
provided Autoconf-like macros for a while. Starting with Autoconf 2.50
in 2001, Autoconf provided versions of these macros, integrated in the
`AC_' namespace, instead of `AM_'. But in order to ease the upgrading
via `autoupdate', bindings to such `AM_' macros are provided.
Unfortunately older versions of Automake (e.g., Automake 1.4) did
not quote the names of these macros. Therefore, when `m4' finds
something like `AC_DEFUN(AM_TYPE_PTRDIFF_T, ...)' in `aclocal.m4',
`AM_TYPE_PTRDIFF_T' is expanded, replaced with its Autoconf definition.
Fortunately Autoconf catches pre-`AC_INIT' expansions, and
complains, in its own words:
$ cat configure.ac
AC_INIT([Example], [1.0], [bug-example@example.org])
AM_TYPE_PTRDIFF_T
$ aclocal-1.4
$ autoconf
aclocal.m4:17: error: m4_defn: undefined macro: _m4_divert_diversion
aclocal.m4:17: the top level
autom4te: m4 failed with exit status: 1
$
Modern versions of Automake no longer define most of these macros,
and properly quote the names of the remaining macros. If you must use
an old Automake, do not depend upon macros from Automake as it is
simply not its job to provide macros (but the one it requires itself):
$ cat configure.ac
AC_INIT([Example], [1.0], [bug-example@example.org])
AM_TYPE_PTRDIFF_T
$ rm aclocal.m4
$ autoupdate
autoupdate: `configure.ac' is updated
$ cat configure.ac
AC_INIT([Example], [1.0], [bug-example@example.org])
AC_CHECK_TYPES([ptrdiff_t])
$ aclocal-1.4
$ autoconf
$

File: autoconf.info, Node: Hosts and Cross-Compilation, Next: AC_LIBOBJ vs LIBOBJS, Prev: New Macros, Up: Autoconf 2.13
17.6.3 Hosts and Cross-Compilation
----------------------------------
Based on the experience of compiler writers, and after long public
debates, many aspects of the cross-compilation chain have changed:
- the relationship between the build, host, and target architecture
types,
- the command line interface for specifying them to `configure',
- the variables defined in `configure',
- the enabling of cross-compilation mode.
The relationship between build, host, and target have been cleaned
up: the chain of default is now simply: target defaults to host, host to
build, and build to the result of `config.guess'. Nevertheless, in
order to ease the transition from 2.13 to 2.50, the following
transition scheme is implemented. _Do not rely on it_, as it will be
completely disabled in a couple of releases (we cannot keep it, as it
proves to cause more problems than it cures).
They all default to the result of running `config.guess', unless you
specify either `--build' or `--host'. In this case, the default
becomes the system type you specified. If you specify both, and
they're different, `configure' enters cross compilation mode, so it
doesn't run any tests that require execution.
Hint: if you mean to override the result of `config.guess', prefer
`--build' over `--host'. In the future, `--host' will not override the
name of the build system type. Whenever you specify `--host', be sure
to specify `--build' too.
For backward compatibility, `configure' accepts a system type as an
option by itself. Such an option overrides the defaults for build,
host, and target system types. The following configure statement
configures a cross toolchain that runs on NetBSD/alpha but generates
code for GNU Hurd/sparc, which is also the build platform.
./configure --host=alpha-netbsd sparc-gnu
In Autoconf 2.13 and before, the variables `build', `host', and
`target' had a different semantics before and after the invocation of
`AC_CANONICAL_BUILD' etc. Now, the argument of `--build' is strictly
copied into `build_alias', and is left empty otherwise. After the
`AC_CANONICAL_BUILD', `build' is set to the canonicalized build type.
To ease the transition, before, its contents is the same as that of
`build_alias'. Do _not_ rely on this broken feature.
For consistency with the backward compatibility scheme exposed above,
when `--host' is specified but `--build' isn't, the build system is
assumed to be the same as `--host', and `build_alias' is set to that
value. Eventually, this historically incorrect behavior will go away.
The former scheme to enable cross-compilation proved to cause more
harm than good, in particular, it used to be triggered too easily,
leaving regular end users puzzled in front of cryptic error messages.
`configure' could even enter cross-compilation mode only because the
compiler was not functional. This is mainly because `configure' used
to try to detect cross-compilation, instead of waiting for an explicit
flag from the user.
Now, `configure' enters cross-compilation mode if and only if
`--host' is passed.
That's the short documentation. To ease the transition between 2.13
and its successors, a more complicated scheme is implemented. _Do not
rely on the following_, as it will be removed in the near future.
If you specify `--host', but not `--build', when `configure'
performs the first compiler test it tries to run an executable produced
by the compiler. If the execution fails, it enters cross-compilation
mode. This is fragile. Moreover, by the time the compiler test is
performed, it may be too late to modify the build-system type: other
tests may have already been performed. Therefore, whenever you specify
`--host', be sure to specify `--build' too.
./configure --build=i686-pc-linux-gnu --host=m68k-coff
enters cross-compilation mode. The former interface, which consisted
in setting the compiler to a cross-compiler without informing
`configure' is obsolete. For instance, `configure' fails if it can't
run the code generated by the specified compiler if you configure as
follows:
./configure CC=m68k-coff-gcc

File: autoconf.info, Node: AC_LIBOBJ vs LIBOBJS, Next: AC_FOO_IFELSE vs AC_TRY_FOO, Prev: Hosts and Cross-Compilation, Up: Autoconf 2.13
17.6.4 `AC_LIBOBJ' vs. `LIBOBJS'
--------------------------------
Up to Autoconf 2.13, the replacement of functions was triggered via the
variable `LIBOBJS'. Since Autoconf 2.50, the macro `AC_LIBOBJ' should
be used instead (*note Generic Functions::). Starting at Autoconf
2.53, the use of `LIBOBJS' is an error.
This change is mandated by the unification of the GNU Build System
components. In particular, the various fragile techniques used to parse
a `configure.ac' are all replaced with the use of traces. As a
consequence, any action must be traceable, which obsoletes critical
variable assignments. Fortunately, `LIBOBJS' was the only problem, and
it can even be handled gracefully (read, "without your having to change
something").
There were two typical uses of `LIBOBJS': asking for a replacement
function, and adjusting `LIBOBJS' for Automake and/or Libtool.
As for function replacement, the fix is immediate: use `AC_LIBOBJ'.
For instance:
LIBOBJS="$LIBOBJS fnmatch.o"
LIBOBJS="$LIBOBJS malloc.$ac_objext"
should be replaced with:
AC_LIBOBJ([fnmatch])
AC_LIBOBJ([malloc])
When used with Automake 1.10 or newer, a suitable value for
`LIBOBJDIR' is set so that the `LIBOBJS' and `LTLIBOBJS' can be
referenced from any `Makefile.am'. Even without Automake, arranging
for `LIBOBJDIR' to be set correctly enables referencing `LIBOBJS' and
`LTLIBOBJS' in another directory. The `LIBOJBDIR' feature is
experimental.

File: autoconf.info, Node: AC_FOO_IFELSE vs AC_TRY_FOO, Prev: AC_LIBOBJ vs LIBOBJS, Up: Autoconf 2.13
17.6.5 `AC_FOO_IFELSE' vs. `AC_TRY_FOO'
---------------------------------------
Since Autoconf 2.50, internal codes uses `AC_PREPROC_IFELSE',
`AC_COMPILE_IFELSE', `AC_LINK_IFELSE', and `AC_RUN_IFELSE' on one hand
and `AC_LANG_SOURCES', and `AC_LANG_PROGRAM' on the other hand instead
of the deprecated `AC_TRY_CPP', `AC_TRY_COMPILE', `AC_TRY_LINK', and
`AC_TRY_RUN'. The motivations where:
- a more consistent interface: `AC_TRY_COMPILE' etc. were double
quoting their arguments;
- the combinatoric explosion is solved by decomposing on the one
hand the generation of sources, and on the other hand executing
the program;
- this scheme helps supporting more languages than plain C and C++.
In addition to the change of syntax, the philosophy has changed too:
while emphasis was put on speed at the expense of accuracy, today's
Autoconf promotes accuracy of the testing framework at, ahem..., the
expense of speed.
As a perfect example of what is _not_ to be done, here is how to
find out whether a header file contains a particular declaration, such
as a typedef, a structure, a structure member, or a function. Use
`AC_EGREP_HEADER' instead of running `grep' directly on the header
file; on some systems the symbol might be defined in another header
file that the file you are checking includes.
As a (bad) example, here is how you should not check for C
preprocessor symbols, either defined by header files or predefined by
the C preprocessor: using `AC_EGREP_CPP':
AC_EGREP_CPP(yes,
[#ifdef _AIX
yes
#endif
], is_aix=yes, is_aix=no)
The above example, properly written would (i) use `AC_LANG_PROGRAM',
and (ii) run the compiler:
AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
[[#ifndef _AIX
error: This isn't AIX!
#endif
]])],
[is_aix=yes],
[is_aix=no])

File: autoconf.info, Node: Using Autotest, Next: FAQ, Prev: Obsolete Constructs, Up: Top
18 Generating Test Suites with Autotest
***************************************
*N.B.: This section describes an experimental feature which will
be part of Autoconf in a forthcoming release. Although we believe
Autotest is stabilizing, this documentation describes an interface which
might change in the future: do not depend upon Autotest without
subscribing to the Autoconf mailing lists.*
It is paradoxical that portable projects depend on nonportable tools
to run their test suite. Autoconf by itself is the paragon of this
problem: although it aims at perfectly portability, up to 2.13 its test
suite was using DejaGNU, a rich and complex testing framework, but
which is far from being standard on Posix systems. Worse yet, it was
likely to be missing on the most fragile platforms, the very platforms
that are most likely to torture Autoconf and exhibit deficiencies.
To circumvent this problem, many package maintainers have developed
their own testing framework, based on simple shell scripts whose sole
outputs are exit status values describing whether the test succeeded.
Most of these tests share common patterns, and this can result in lots
of duplicated code and tedious maintenance.
Following exactly the same reasoning that yielded to the inception of
Autoconf, Autotest provides a test suite generation framework, based on
M4 macros building a portable shell script. The suite itself is
equipped with automatic logging and tracing facilities which greatly
diminish the interaction with bug reporters, and simple timing reports.
Autoconf itself has been using Autotest for years, and we do attest
that it has considerably improved the strength of the test suite and the
quality of bug reports. Other projects are known to use some generation
of Autotest, such as Bison, Free Recode, Free Wdiff, GNU Tar, each of
them with different needs, and this usage has validated Autotest as a
general testing framework.
Nonetheless, compared to DejaGNU, Autotest is inadequate for
interactive tool testing, which is probably its main limitation.
* Menu:
* Using an Autotest Test Suite:: Autotest and the user
* Writing testsuite.at:: Autotest macros
* testsuite Invocation:: Running `testsuite' scripts
* Making testsuite Scripts:: Using autom4te to create `testsuite'

File: autoconf.info, Node: Using an Autotest Test Suite, Next: Writing testsuite.at, Up: Using Autotest
18.1 Using an Autotest Test Suite
=================================
* Menu:
* testsuite Scripts:: The concepts of Autotest
* Autotest Logs:: Their contents

File: autoconf.info, Node: testsuite Scripts, Next: Autotest Logs, Up: Using an Autotest Test Suite
18.1.1 `testsuite' Scripts
--------------------------
Generating testing or validation suites using Autotest is rather easy.
The whole validation suite is held in a file to be processed through
`autom4te', itself using GNU M4 under the scene, to produce a
stand-alone Bourne shell script which then gets distributed. Neither
`autom4te' nor GNU M4 are needed at the installer's end.
Each test of the validation suite should be part of some test group.
A "test group" is a sequence of interwoven tests that ought to be
executed together, usually because one test in the group creates data
files than a later test in the same group needs to read. Complex test
groups make later debugging more tedious. It is much better to keep
only a few tests per test group. Ideally there is only one test per
test group.
For all but the simplest packages, some file such as `testsuite.at'
does not fully hold all test sources, as these are often easier to
maintain in separate files. Each of these separate files holds a single
test group, or a sequence of test groups all addressing some common
functionality in the package. In such cases, `testsuite.at' merely
initializes the validation suite, and sometimes does elementary health
checking, before listing include statements for all other test files.
The special file `package.m4', containing the identification of the
package, is automatically included if found.
A convenient alternative consists in moving all the global issues
(local Autotest macros, elementary health checking, and `AT_INIT'
invocation) into the file `local.at', and making `testsuite.at' be a
simple list of `m4_include' of sub test suites. In such case,
generating the whole test suite or pieces of it is only a matter of
choosing the `autom4te' command line arguments.
The validation scripts that Autotest produces are by convention
called `testsuite'. When run, `testsuite' executes each test group in
turn, producing only one summary line per test to say if that
particular test succeeded or failed. At end of all tests, summarizing
counters get printed. One debugging directory is left for each test
group which failed, if any: such directories are named
`testsuite.dir/NN', where NN is the sequence number of the test group,
and they include:
* a debugging script named `run' which reruns the test in "debug
mode" (*note testsuite Invocation::). The automatic generation of
debugging scripts has the purpose of easing the chase for bugs.
* all the files created with `AT_DATA'
* a log of the run, named `testsuite.log'
In the ideal situation, none of the tests fail, and consequently no
debugging directory is left behind for validation.
It often happens in practice that individual tests in the validation
suite need to get information coming out of the configuration process.
Some of this information, common for all validation suites, is provided
through the file `atconfig', automatically created by
`AC_CONFIG_TESTDIR'. For configuration informations which your testing
environment specifically needs, you might prepare an optional file
named `atlocal.in', instantiated by `AC_CONFIG_FILES'. The
configuration process produces `atconfig' and `atlocal' out of these
two input files, and these two produced files are automatically read by
the `testsuite' script.
Here is a diagram showing the relationship between files.
Files used in preparing a software package for distribution:
[package.m4] -->.
\
subfile-1.at ->. [local.at] ---->+
... \ \
subfile-i.at ---->-- testsuite.at -->-- autom4te* -->testsuite
... /
subfile-n.at ->'
Files used in configuring a software package:
.--> atconfig
/
[atlocal.in] --> config.status* --<
\
`--> [atlocal]
Files created during the test suite execution:
atconfig -->. .--> testsuite.log
\ /
>-- testsuite* --<
/ \
[atlocal] ->' `--> [testsuite.dir]

File: autoconf.info, Node: Autotest Logs, Prev: testsuite Scripts, Up: Using an Autotest Test Suite
18.1.2 Autotest Logs
--------------------
When run, the test suite creates a log file named after itself, e.g., a
test suite named `testsuite' creates `testsuite.log'. It contains a
lot of information, usually more than maintainers actually need, but
therefore most of the time it contains all that is needed:
command line arguments
A bad but unfortunately widespread habit consists of setting
environment variables before the command, such as in
`CC=my-home-grown-cc ./testsuite'. The test suite does not know
this change, hence (i) it cannot report it to you, and (ii) it
cannot preserve the value of `CC' for subsequent runs. Autoconf
faced exactly the same problem, and solved it by asking users to
pass the variable definitions as command line arguments. Autotest
requires this rule, too, but has no means to enforce it; the log
then contains a trace of the variables that were changed by the
user.
`ChangeLog' excerpts
The topmost lines of all the `ChangeLog' files found in the source
hierarchy. This is especially useful when bugs are reported
against development versions of the package, since the version
string does not provide sufficient information to know the exact
state of the sources the user compiled. Of course, this relies on
the use of a `ChangeLog'.
build machine
Running a test suite in a cross-compile environment is not an easy
task, since it would mean having the test suite run on a machine
BUILD, while running programs on a machine HOST. It is much
simpler to run both the test suite and the programs on HOST, but
then, from the point of view of the test suite, there remains a
single environment, HOST = BUILD. The log contains relevant
information on the state of the build machine, including some
important environment variables.
tested programs
The absolute file name and answers to `--version' of the tested
programs (see *Note Writing testsuite.at::, `AT_TESTED').
configuration log
The contents of `config.log', as created by `configure', are
appended. It contains the configuration flags and a detailed
report on the configuration itself.

File: autoconf.info, Node: Writing testsuite.at, Next: testsuite Invocation, Prev: Using an Autotest Test Suite, Up: Using Autotest
18.2 Writing `testsuite.at'
===========================
The `testsuite.at' is a Bourne shell script making use of special
Autotest M4 macros. It often contains a call to `AT_INIT' near its
beginning followed by one call to `m4_include' per source file for
tests. Each such included file, or the remainder of `testsuite.at' if
include files are not used, contain a sequence of test groups. Each
test group begins with a call to `AT_SETUP', then an arbitrary number
of shell commands or calls to `AT_CHECK', and then completes with a
call to `AT_CLEANUP'.
-- Macro: AT_INIT ([NAME])
Initialize Autotest. Giving a NAME to the test suite is
encouraged if your package includes several test suites. In any
case, the test suite always displays the package name and version.
It also inherits the package bug report address.
-- Macro: AT_COPYRIGHT (COPYRIGHT-NOTICE)
State that, in addition to the Free Software Foundation's
copyright on the Autotest macros, parts of your test suite are
covered by COPYRIGHT-NOTICE.
The COPYRIGHT-NOTICE shows up in both the head of `testsuite' and
in `testsuite --version'.
-- Macro: AT_TESTED (EXECUTABLES)
Log the file name and answer to `--version' of each program in
space-separated list EXECUTABLES. Several invocations register
new executables, in other words, don't fear registering one program
several times.
Autotest test suites rely on `PATH' to find the tested program.
This avoids the need to generate absolute names of the various tools,
and makes it possible to test installed programs. Therefore, knowing
which programs are being exercised is crucial to understanding problems
in the test suite itself, or its occasional misuses. It is a good idea
to also subscribe foreign programs you depend upon, to avoid
incompatible diagnostics.
-- Macro: AT_SETUP (TEST-GROUP-NAME)
This macro starts a group of related tests, all to be executed in
the same subshell. It accepts a single argument, which holds a
few words (no more than about 30 or 40 characters) quickly
describing the purpose of the test group being started.
-- Macro: AT_KEYWORDS (KEYWORDS)
Associate the space-separated list of KEYWORDS to the enclosing
test group. This makes it possible to run "slices" of the test
suite. For instance, if some of your test groups exercise some
`foo' feature, then using `AT_KEYWORDS(foo)' lets you run
`./testsuite -k foo' to run exclusively these test groups. The
TITLE of the test group is automatically recorded to `AT_KEYWORDS'.
Several invocations within a test group accumulate new keywords.
In other words, don't fear registering the same keyword several
times in a test group.
-- Macro: AT_CAPTURE_FILE (FILE)
If the current test group fails, log the contents of FILE.
Several identical calls within one test group have no additional
effect.
-- Macro: AT_XFAIL_IF (SHELL-CONDITION)
Determine whether the test is expected to fail because it is a
known bug (for unsupported features, you should skip the test).
SHELL-CONDITION is a shell expression such as a `test' command;
you can instantiate this macro many times from within the same
test group, and one of the conditions is enough to turn the test
into an expected failure.
-- Macro: AT_CLEANUP
End the current test group.
-- Macro: AT_DATA (FILE, CONTENTS)
Initialize an input data FILE with given CONTENTS. Of course, the
CONTENTS have to be properly quoted between square brackets to
protect against included commas or spurious M4 expansion. The
contents ought to end with an end of line.
-- Macro: AT_CHECK (COMMANDS, [STATUS = `0'], [STDOUT = `'], [STDERR =
`'], [RUN-IF-FAIL], [RUN-IF-PASS])
Execute a test by performing given shell COMMANDS. These commands
should normally exit with STATUS, while producing expected STDOUT
and STDERR contents. If COMMANDS exit with status 77, then the
whole test group is skipped. Otherwise, if this test fails, run
shell commands RUN-IF-FAIL or, if this test passes, run shell
commands RUN-IF-PASS.
The COMMANDS _must not_ redirect the standard output, nor the
standard error.
If STATUS, or STDOUT, or STDERR is `ignore', then the
corresponding value is not checked.
The special value `expout' for STDOUT means the expected output of
the COMMANDS is the content of the file `expout'. If STDOUT is
`stdout', then the standard output of the COMMANDS is available
for further tests in the file `stdout'. Similarly for STDERR with
`experr' and `stderr'.

File: autoconf.info, Node: testsuite Invocation, Next: Making testsuite Scripts, Prev: Writing testsuite.at, Up: Using Autotest
18.3 Running `testsuite' Scripts
================================
Autotest test suites support the following arguments:
`--help'
`-h'
Display the list of options and exit successfully.
`--version'
`-V'
Display the version of the test suite and exit successfully.
`--clean'
`-c'
Remove all the files the test suite might have created and exit.
Meant for `clean' Make targets.
`--list'
`-l'
List all the tests (or only the selection), including their
possible keywords.
By default all tests are performed (or described with `--list') in
the default environment first silently, then verbosely, but the
environment, set of tests, and verbosity level can be tuned:
`VARIABLE=VALUE'
Set the environment VARIABLE to VALUE. Use this rather than
`FOO=foo ./testsuite' as debugging scripts would then run in a
different environment.
The variable `AUTOTEST_PATH' specifies the testing path to prepend
to `PATH'. Relative directory names (not starting with `/') are
considered to be relative to the top level of the package being
built. All directories are made absolute, first starting from the
top level _build_ tree, then from the _source_ tree. For instance
`./testsuite AUTOTEST_PATH=tests:bin' for a `/src/foo-1.0' source
package built in `/tmp/foo' results in
`/tmp/foo/tests:/tmp/foo/bin' and then
`/src/foo-1.0/tests:/src/foo-1.0/bin' being prepended to `PATH'.
`NUMBER'
`NUMBER-NUMBER'
`NUMBER-'
`-NUMBER'
Add the corresponding test groups, with obvious semantics, to the
selection.
`--keywords=KEYWORDS'
`-k KEYWORDS'
Add to the selection the test groups with title or keywords
(arguments to `AT_SETUP' or `AT_KEYWORDS') that match _all_
keywords of the comma separated list KEYWORDS, case-insensitively.
Use `!' immediately before the keyword to invert the selection
for this keyword. By default, the keywords match whole words;
enclose them in `.*' to also match parts of words.
For example, running
./testsuite -k 'autoupdate,.*FUNC.*'
selects all tests tagged `autoupdate' _and_ with tags containing
`FUNC' (as in `AC_CHECK_FUNC', `AC_FUNC_ALLOCA', etc.), while
./testsuite -k '!autoupdate' -k '.*FUNC.*'
selects all tests not tagged `autoupdate' _or_ with tags
containing `FUNC'.
`--errexit'
`-e'
If any test fails, immediately abort testing. It implies
`--debug': post test group clean up, and top-level logging are
inhibited. This option is meant for the full test suite, it is
not really useful for generated debugging scripts.
`--verbose'
`-v'
Force more verbosity in the detailed output of what is being done.
This is the default for debugging scripts.
`--debug'
`-d'
Do not remove the files after a test group was performed --but
they are still removed _before_, therefore using this option is
sane when running several test groups. Create debugging scripts.
Do not overwrite the top-level log (in order to preserve
supposedly existing full log file). This is the default for
debugging scripts, but it can also be useful to debug the
testsuite itself.
`--trace'
`-x'
Trigger shell tracing of the test groups.

File: autoconf.info, Node: Making testsuite Scripts, Prev: testsuite Invocation, Up: Using Autotest
18.4 Making `testsuite' Scripts
===============================
For putting Autotest into movement, you need some configuration and
makefile machinery. We recommend, at least if your package uses deep or
shallow hierarchies, that you use `tests/' as the name of the directory
holding all your tests and their makefile. Here is a check list of
things to do.
- Make sure to create the file `package.m4', which defines the
identity of the package. It must define `AT_PACKAGE_STRING', the
full signature of the package, and `AT_PACKAGE_BUGREPORT', the
address to which bug reports should be sent. For sake of
completeness, we suggest that you also define `AT_PACKAGE_NAME',
`AT_PACKAGE_TARNAME', and `AT_PACKAGE_VERSION'. *Note
Initializing configure::, for a description of these variables. We
suggest the following makefile excerpt:
$(srcdir)/package.m4: $(top_srcdir)/configure.ac
{ \
echo '# Signature of the current package.'; \
echo 'm4_define([AT_PACKAGE_NAME], [@PACKAGE_NAME@])'; \
echo 'm4_define([AT_PACKAGE_TARNAME], [@PACKAGE_TARNAME@])'; \
echo 'm4_define([AT_PACKAGE_VERSION], [@PACKAGE_VERSION@])'; \
echo 'm4_define([AT_PACKAGE_STRING], [@PACKAGE_STRING@])'; \
echo 'm4_define([AT_PACKAGE_BUGREPORT], [@PACKAGE_BUGREPORT@])'; \
} >'$(srcdir)/package.m4'
Be sure to distribute `package.m4' and to put it into the source
hierarchy: the test suite ought to be shipped!
- Invoke `AC_CONFIG_TESTDIR'.
-- Macro: AC_CONFIG_TESTDIR (DIRECTORY, [TEST-PATH = `directory'])
An Autotest test suite is to be configured in DIRECTORY. This
macro requires the instantiation of `DIRECTORY/atconfig' from
`DIRECTORY/atconfig.in', and sets the default `AUTOTEST_PATH'
to TEST-PATH (*note testsuite Invocation::).
- Still within `configure.ac', as appropriate, ensure that some
`AC_CONFIG_FILES' command includes substitution for
`tests/atlocal'.
- The `tests/Makefile.in' should be modified so the validation in
your package is triggered by `make check'. An example is provided
below.
With Automake, here is a minimal example about how to link `make
check' with a validation suite.
EXTRA_DIST = testsuite.at $(TESTSUITE) atlocal.in
TESTSUITE = $(srcdir)/testsuite
check-local: atconfig atlocal $(TESTSUITE)
$(SHELL) '$(TESTSUITE)' $(TESTSUITEFLAGS)
installcheck-local: atconfig atlocal $(TESTSUITE)
$(SHELL) '$(TESTSUITE)' AUTOTEST_PATH='$(bindir)' \
$(TESTSUITEFLAGS)
clean-local:
test ! -f '$(TESTSUITE)' || \
$(SHELL) '$(TESTSUITE)' --clean
AUTOTEST = $(AUTOM4TE) --language=autotest
$(TESTSUITE): $(srcdir)/testsuite.at
$(AUTOTEST) -I '$(srcdir)' -o $@.tmp $@.at
mv $@.tmp $@
You might want to list explicitly the dependencies, i.e., the list of
the files `testsuite.at' includes.
With strict Autoconf, you might need to add lines inspired from the
following:
subdir = tests
atconfig: $(top_builddir)/config.status
cd $(top_builddir) && \
$(SHELL) ./config.status $(subdir)/$@
atlocal: $(srcdir)/atlocal.in $(top_builddir)/config.status
cd $(top_builddir) && \
$(SHELL) ./config.status $(subdir)/$@
and manage to have `atconfig.in' and `$(EXTRA_DIST)' distributed.
With all this in place, and if you have not initialized
`TESTSUITEFLAGS' within your makefile, you can fine-tune test suite
execution with this variable, for example:
make check TESTSUITEFLAGS='-v -d -x 75 -k AC_PROG_CC CFLAGS=-g'

File: autoconf.info, Node: FAQ, Next: History, Prev: Using Autotest, Up: Top
19 Frequent Autoconf Questions, with answers
********************************************
Several questions about Autoconf come up occasionally. Here some of
them are addressed.
* Menu:
* Distributing:: Distributing `configure' scripts
* Why GNU M4:: Why not use the standard M4?
* Bootstrapping:: Autoconf and GNU M4 require each other?
* Why Not Imake:: Why GNU uses `configure' instead of Imake
* Defining Directories:: Passing `datadir' to program
* autom4te.cache:: What is it? Can I remove it?
* Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree

File: autoconf.info, Node: Distributing, Next: Why GNU M4, Up: FAQ
19.1 Distributing `configure' Scripts
=====================================
What are the restrictions on distributing `configure'
scripts that Autoconf generates? How does that affect my
programs that use them?
There are no restrictions on how the configuration scripts that
Autoconf produces may be distributed or used. In Autoconf version 1,
they were covered by the GNU General Public License. We still encourage
software authors to distribute their work under terms like those of the
GPL, but doing so is not required to use Autoconf.
Of the other files that might be used with `configure',
`config.h.in' is under whatever copyright you use for your
`configure.ac'. `config.sub' and `config.guess' have an exception to
the GPL when they are used with an Autoconf-generated `configure'
script, which permits you to distribute them under the same terms as
the rest of your package. `install-sh' is from the X Consortium and is
not copyrighted.

File: autoconf.info, Node: Why GNU M4, Next: Bootstrapping, Prev: Distributing, Up: FAQ
19.2 Why Require GNU M4?
========================
Why does Autoconf require GNU M4?
Many M4 implementations have hard-coded limitations on the size and
number of macros that Autoconf exceeds. They also lack several builtin
macros that it would be difficult to get along without in a
sophisticated application like Autoconf, including:
m4_builtin
m4_indir
m4_bpatsubst
__file__
__line__
Autoconf requires version 1.4.7 or later of GNU M4.
Since only software maintainers need to use Autoconf, and since GNU
M4 is simple to configure and install, it seems reasonable to require
GNU M4 to be installed also. Many maintainers of GNU and other free
software already have most of the GNU utilities installed, since they
prefer them.

File: autoconf.info, Node: Bootstrapping, Next: Why Not Imake, Prev: Why GNU M4, Up: FAQ
19.3 How Can I Bootstrap?
=========================
If Autoconf requires GNU M4 and GNU M4 has an Autoconf
`configure' script, how do I bootstrap? It seems like a chicken
and egg problem!
This is a misunderstanding. Although GNU M4 does come with a
`configure' script produced by Autoconf, Autoconf is not required in
order to run the script and install GNU M4. Autoconf is only required
if you want to change the M4 `configure' script, which few people have
to do (mainly its maintainer).

File: autoconf.info, Node: Why Not Imake, Next: Defining Directories, Prev: Bootstrapping, Up: FAQ
19.4 Why Not Imake?
===================
Why not use Imake instead of `configure' scripts?
Several people have written addressing this question, so I include
adaptations of their explanations here.
The following answer is based on one written by Richard Pixley:
Autoconf generated scripts frequently work on machines that it has
never been set up to handle before. That is, it does a good job of
inferring a configuration for a new system. Imake cannot do this.
Imake uses a common database of host specific data. For X11, this
makes sense because the distribution is made as a collection of
tools, by one central authority who has control over the database.
GNU tools are not released this way. Each GNU tool has a
maintainer; these maintainers are scattered across the world.
Using a common database would be a maintenance nightmare.
Autoconf may appear to be this kind of database, but in fact it is
not. Instead of listing host dependencies, it lists program
requirements.
If you view the GNU suite as a collection of native tools, then the
problems are similar. But the GNU development tools can be
configured as cross tools in almost any host+target permutation.
All of these configurations can be installed concurrently. They
can even be configured to share host independent files across
hosts. Imake doesn't address these issues.
Imake templates are a form of standardization. The GNU coding
standards address the same issues without necessarily imposing the
same restrictions.
Here is some further explanation, written by Per Bothner:
One of the advantages of Imake is that it easy to generate large
makefiles using the `#include' and macro mechanisms of `cpp'.
However, `cpp' is not programmable: it has limited conditional
facilities, and no looping. And `cpp' cannot inspect its
environment.
All of these problems are solved by using `sh' instead of `cpp'.
The shell is fully programmable, has macro substitution, can
execute (or source) other shell scripts, and can inspect its
environment.
Paul Eggert elaborates more:
With Autoconf, installers need not assume that Imake itself is
already installed and working well. This may not seem like much
of an advantage to people who are accustomed to Imake. But on
many hosts Imake is not installed or the default installation is
not working well, and requiring Imake to install a package hinders
the acceptance of that package on those hosts. For example, the
Imake template and configuration files might not be installed
properly on a host, or the Imake build procedure might wrongly
assume that all source files are in one big directory tree, or the
Imake configuration might assume one compiler whereas the package
or the installer needs to use another, or there might be a version
mismatch between the Imake expected by the package and the Imake
supported by the host. These problems are much rarer with
Autoconf, where each package comes with its own independent
configuration processor.
Also, Imake often suffers from unexpected interactions between
`make' and the installer's C preprocessor. The fundamental problem
here is that the C preprocessor was designed to preprocess C
programs, not makefiles. This is much less of a problem with
Autoconf, which uses the general-purpose preprocessor M4, and
where the package's author (rather than the installer) does the
preprocessing in a standard way.
Finally, Mark Eichin notes:
Imake isn't all that extensible, either. In order to add new
features to Imake, you need to provide your own project template,
and duplicate most of the features of the existing one. This
means that for a sophisticated project, using the vendor-provided
Imake templates fails to provide any leverage--since they don't
cover anything that your own project needs (unless it is an X11
program).
On the other side, though:
The one advantage that Imake has over `configure': `Imakefile'
files tend to be much shorter (likewise, less redundant) than
`Makefile.in' files. There is a fix to this, however--at least
for the Kerberos V5 tree, we've modified things to call in common
`post.in' and `pre.in' makefile fragments for the entire tree.
This means that a lot of common things don't have to be
duplicated, even though they normally are in `configure' setups.

File: autoconf.info, Node: Defining Directories, Next: autom4te.cache, Prev: Why Not Imake, Up: FAQ
19.5 How Do I `#define' Installation Directories?
=================================================
My program needs library files, installed in `datadir' and
similar. If I use
AC_DEFINE_UNQUOTED([DATADIR], [$datadir],
[Define to the read-only architecture-independent
data directory.])
I get
#define DATADIR "${prefix}/share"
As already explained, this behavior is on purpose, mandated by the GNU
Coding Standards, see *Note Installation Directory Variables::. There
are several means to achieve a similar goal:
- Do not use `AC_DEFINE' but use your makefile to pass the actual
value of `datadir' via compilation flags. *Note Installation
Directory Variables::, for the details.
- This solution can be simplified when compiling a program: you may
either extend the `CPPFLAGS':
CPPFLAGS = -DDATADIR='"$(datadir)"' @CPPFLAGS@
or create a dedicated header file:
DISTCLEANFILES = datadir.h
datadir.h: Makefile
echo '#define DATADIR "$(datadir)"' >$@
- Use `AC_DEFINE' but have `configure' compute the literal value of
`datadir' and others. Many people have wrapped macros to automate
this task. For instance, the macro `AC_DEFINE_DIR' from the
Autoconf Macro Archive (http://autoconf-archive.cryp.to/).
This solution does not conform to the GNU Coding Standards.
- Note that all the previous solutions hard wire the absolute name of
these directories in the executables, which is not a good
property. You may try to compute the names relative to `prefix',
and try to find `prefix' at runtime, this way your package is
relocatable. Some macros are already available to address this
issue: see `adl_COMPUTE_RELATIVE_PATHS' and
`adl_COMPUTE_STANDARD_RELATIVE_PATHS' on the Autoconf Macro
Archive (http://autoconf-archive.cryp.to/).

File: autoconf.info, Node: autom4te.cache, Next: Present But Cannot Be Compiled, Prev: Defining Directories, Up: FAQ
19.6 What is `autom4te.cache'?
==============================
What is this directory `autom4te.cache'? Can I safely remove it?
In the GNU Build System, `configure.ac' plays a central role and is
read by many tools: `autoconf' to create `configure', `autoheader' to
create `config.h.in', `automake' to create `Makefile.in', `autoscan' to
check the completeness of `configure.ac', `autoreconf' to check the GNU
Build System components that are used. To "read `configure.ac'"
actually means to compile it with M4, which can be a long process for
complex `configure.ac'.
This is why all these tools, instead of running directly M4, invoke
`autom4te' (*note autom4te Invocation::) which, while answering to a
specific demand, stores additional information in `autom4te.cache' for
future runs. For instance, if you run `autoconf', behind the scenes,
`autom4te' also stores information for the other tools, so that when
you invoke `autoheader' or `automake' etc., reprocessing `configure.ac'
is not needed. The speed up is frequently of 30%, and is increasing
with the size of `configure.ac'.
But it is and remains being simply a cache: you can safely remove it.
Can I permanently get rid of it?
The creation of this cache can be disabled from `~/.autom4te.cfg',
see *Note Customizing autom4te::, for more details. You should be
aware that disabling the cache slows down the Autoconf test suite by
40%. The more GNU Build System components are used, the more the cache
is useful; for instance running `autoreconf -f' on the Core Utilities
is twice slower without the cache _although `--force' implies that the
cache is not fully exploited_, and eight times slower than without
`--force'.

File: autoconf.info, Node: Present But Cannot Be Compiled, Prev: autom4te.cache, Up: FAQ
19.7 Header Present But Cannot Be Compiled
==========================================
The most important guideline to bear in mind when checking for features
is to mimic as much as possible the intended use. Unfortunately, old
versions of `AC_CHECK_HEADER' and `AC_CHECK_HEADERS' failed to follow
this idea, and called the preprocessor, instead of the compiler, to
check for headers. As a result, incompatibilities between headers went
unnoticed during configuration, and maintainers finally had to deal
with this issue elsewhere.
As of Autoconf 2.56 both checks are performed, and `configure'
complains loudly if the compiler and the preprocessor do not agree.
For the time being the result used is that of the preprocessor, to give
maintainers time to adjust their `configure.ac', but in the future,
only the compiler will be considered.
Consider the following example:
$ cat number.h
typedef int number;
$ cat pi.h
const number pi = 3;
$ cat configure.ac
AC_INIT([Example], [1.0], [bug-example@example.org])
AC_CHECK_HEADERS([pi.h])
$ autoconf -Wall
$ ./configure
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -E
checking for grep that handles long lines and -e... grep
checking for egrep... grep -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking pi.h usability... no
checking pi.h presence... yes
configure: WARNING: pi.h: present but cannot be compiled
configure: WARNING: pi.h: check for missing prerequisite headers?
configure: WARNING: pi.h: see the Autoconf documentation
configure: WARNING: pi.h: section "Present But Cannot Be Compiled"
configure: WARNING: pi.h: proceeding with the preprocessor's result
configure: WARNING: pi.h: in the future, the compiler will take precedence
configure: WARNING: ## -------------------------------------- ##
configure: WARNING: ## Report this to bug-example@example.org ##
configure: WARNING: ## -------------------------------------- ##
checking for pi.h... yes
The proper way the handle this case is using the fourth argument (*note
Generic Headers::):
$ cat configure.ac
AC_INIT([Example], [1.0], [bug-example@example.org])
AC_CHECK_HEADERS([number.h pi.h], [], [],
[[#ifdef HAVE_NUMBER_H
# include <number.h>
#endif
]])
$ autoconf -Wall
$ ./configure
checking for gcc... gcc
checking for C compiler default output... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ANSI C... none needed
checking for number.h... yes
checking for pi.h... yes
See *Note Particular Headers::, for a list of headers with their
prerequisite.

File: autoconf.info, Node: History, Next: Copying This Manual, Prev: FAQ, Up: Top
20 History of Autoconf
**********************
You may be wondering, Why was Autoconf originally written? How did it
get into its present form? (Why does it look like gorilla spit?) If
you're not wondering, then this chapter contains no information useful
to you, and you might as well skip it. If you _are_ wondering, then
let there be light....
* Menu:
* Genesis:: Prehistory and naming of `configure'
* Exodus:: The plagues of M4 and Perl
* Leviticus:: The priestly code of portability arrives
* Numbers:: Growth and contributors
* Deuteronomy:: Approaching the promises of easy configuration

File: autoconf.info, Node: Genesis, Next: Exodus, Up: History
20.1 Genesis
============
In June 1991 I was maintaining many of the GNU utilities for the Free
Software Foundation. As they were ported to more platforms and more
programs were added, the number of `-D' options that users had to
select in the makefile (around 20) became burdensome. Especially for
me--I had to test each new release on a bunch of different systems. So
I wrote a little shell script to guess some of the correct settings for
the fileutils package, and released it as part of fileutils 2.0. That
`configure' script worked well enough that the next month I adapted it
(by hand) to create similar `configure' scripts for several other GNU
utilities packages. Brian Berliner also adapted one of my scripts for
his CVS revision control system.
Later that summer, I learned that Richard Stallman and Richard Pixley
were developing similar scripts to use in the GNU compiler tools; so I
adapted my `configure' scripts to support their evolving interface:
using the file name `Makefile.in' as the templates; adding `+srcdir',
the first option (of many); and creating `config.status' files.

File: autoconf.info, Node: Exodus, Next: Leviticus, Prev: Genesis, Up: History
20.2 Exodus
===========
As I got feedback from users, I incorporated many improvements, using
Emacs to search and replace, cut and paste, similar changes in each of
the scripts. As I adapted more GNU utilities packages to use
`configure' scripts, updating them all by hand became impractical.
Rich Murphey, the maintainer of the GNU graphics utilities, sent me
mail saying that the `configure' scripts were great, and asking if I
had a tool for generating them that I could send him. No, I thought,
but I should! So I started to work out how to generate them. And the
journey from the slavery of hand-written `configure' scripts to the
abundance and ease of Autoconf began.
Cygnus `configure', which was being developed at around that time,
is table driven; it is meant to deal mainly with a discrete number of
system types with a small number of mainly unguessable features (such as
details of the object file format). The automatic configuration system
that Brian Fox had developed for Bash takes a similar approach. For
general use, it seems to me a hopeless cause to try to maintain an
up-to-date database of which features each variant of each operating
system has. It's easier and more reliable to check for most features on
the fly--especially on hybrid systems that people have hacked on
locally or that have patches from vendors installed.
I considered using an architecture similar to that of Cygnus
`configure', where there is a single `configure' script that reads
pieces of `configure.in' when run. But I didn't want to have to
distribute all of the feature tests with every package, so I settled on
having a different `configure' made from each `configure.in' by a
preprocessor. That approach also offered more control and flexibility.
I looked briefly into using the Metaconfig package, by Larry Wall,
Harlan Stenn, and Raphael Manfredi, but I decided not to for several
reasons. The `Configure' scripts it produces are interactive, which I
find quite inconvenient; I didn't like the ways it checked for some
features (such as library functions); I didn't know that it was still
being maintained, and the `Configure' scripts I had seen didn't work on
many modern systems (such as System V R4 and NeXT); it wasn't flexible
in what it could do in response to a feature's presence or absence; I
found it confusing to learn; and it was too big and complex for my
needs (I didn't realize then how much Autoconf would eventually have to
grow).
I considered using Perl to generate my style of `configure' scripts,
but decided that M4 was better suited to the job of simple textual
substitutions: it gets in the way less, because output is implicit.
Plus, everyone already has it. (Initially I didn't rely on the GNU
extensions to M4.) Also, some of my friends at the University of
Maryland had recently been putting M4 front ends on several programs,
including `tvtwm', and I was interested in trying out a new language.

File: autoconf.info, Node: Leviticus, Next: Numbers, Prev: Exodus, Up: History
20.3 Leviticus
==============
Since my `configure' scripts determine the system's capabilities
automatically, with no interactive user intervention, I decided to call
the program that generates them Autoconfig. But with a version number
tacked on, that name would be too long for old Unix file systems, so I
shortened it to Autoconf.
In the fall of 1991 I called together a group of fellow questers
after the Holy Grail of portability (er, that is, alpha testers) to
give me feedback as I encapsulated pieces of my handwritten scripts in
M4 macros and continued to add features and improve the techniques used
in the checks. Prominent among the testers were Franc,ois Pinard, who
came up with the idea of making an Autoconf shell script to run M4 and
check for unresolved macro calls; Richard Pixley, who suggested running
the compiler instead of searching the file system to find include files
and symbols, for more accurate results; Karl Berry, who got Autoconf to
configure TeX and added the macro index to the documentation; and Ian
Lance Taylor, who added support for creating a C header file as an
alternative to putting `-D' options in a makefile, so he could use
Autoconf for his UUCP package. The alpha testers cheerfully adjusted
their files again and again as the names and calling conventions of the
Autoconf macros changed from release to release. They all contributed
many specific checks, great ideas, and bug fixes.

File: autoconf.info, Node: Numbers, Next: Deuteronomy, Prev: Leviticus, Up: History
20.4 Numbers
============
In July 1992, after months of alpha testing, I released Autoconf 1.0,
and converted many GNU packages to use it. I was surprised by how
positive the reaction to it was. More people started using it than I
could keep track of, including people working on software that wasn't
part of the GNU Project (such as TCL, FSP, and Kerberos V5). Autoconf
continued to improve rapidly, as many people using the `configure'
scripts reported problems they encountered.
Autoconf turned out to be a good torture test for M4 implementations.
Unix M4 started to dump core because of the length of the macros that
Autoconf defined, and several bugs showed up in GNU M4 as well.
Eventually, we realized that we needed to use some features that only
GNU M4 has. 4.3BSD M4, in particular, has an impoverished set of
builtin macros; the System V version is better, but still doesn't
provide everything we need.
More development occurred as people put Autoconf under more stresses
(and to uses I hadn't anticipated). Karl Berry added checks for X11.
david zuhn contributed C++ support. Franc,ois Pinard made it diagnose
invalid arguments. Jim Blandy bravely coerced it into configuring GNU
Emacs, laying the groundwork for several later improvements. Roland
McGrath got it to configure the GNU C Library, wrote the `autoheader'
script to automate the creation of C header file templates, and added a
`--verbose' option to `configure'. Noah Friedman added the
`--autoconf-dir' option and `AC_MACRODIR' environment variable. (He
also coined the term "autoconfiscate" to mean "adapt a software package
to use Autoconf".) Roland and Noah improved the quoting protection in
`AC_DEFINE' and fixed many bugs, especially when I got sick of dealing
with portability problems from February through June, 1993.

File: autoconf.info, Node: Deuteronomy, Prev: Numbers, Up: History
20.5 Deuteronomy
================
A long wish list for major features had accumulated, and the effect of
several years of patching by various people had left some residual
cruft. In April 1994, while working for Cygnus Support, I began a major
revision of Autoconf. I added most of the features of the Cygnus
`configure' that Autoconf had lacked, largely by adapting the relevant
parts of Cygnus `configure' with the help of david zuhn and Ken
Raeburn. These features include support for using `config.sub',
`config.guess', `--host', and `--target'; making links to files; and
running `configure' scripts in subdirectories. Adding these features
enabled Ken to convert GNU `as', and Rob Savoye to convert DejaGNU, to
using Autoconf.
I added more features in response to other peoples' requests. Many
people had asked for `configure' scripts to share the results of the
checks between runs, because (particularly when configuring a large
source tree, like Cygnus does) they were frustratingly slow. Mike
Haertel suggested adding site-specific initialization scripts. People
distributing software that had to unpack on MS-DOS asked for a way to
override the `.in' extension on the file names, which produced file
names like `config.h.in' containing two dots. Jim Avera did an
extensive examination of the problems with quoting in `AC_DEFINE' and
`AC_SUBST'; his insights led to significant improvements. Richard
Stallman asked that compiler output be sent to `config.log' instead of
`/dev/null', to help people debug the Emacs `configure' script.
I made some other changes because of my dissatisfaction with the
quality of the program. I made the messages showing results of the
checks less ambiguous, always printing a result. I regularized the
names of the macros and cleaned up coding style inconsistencies. I
added some auxiliary utilities that I had developed to help convert
source code packages to use Autoconf. With the help of Franc,ois
Pinard, I made the macros not interrupt each others' messages. (That
feature revealed some performance bottlenecks in GNU M4, which he
hastily corrected!) I reorganized the documentation around problems
people want to solve. And I began a test suite, because experience had
shown that Autoconf has a pronounced tendency to regress when we change
it.
Again, several alpha testers gave invaluable feedback, especially
Franc,ois Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn,
and Mark Eichin.
Finally, version 2.0 was ready. And there was much rejoicing. (And
I have free time again. I think. Yeah, right.)

File: autoconf.info, Node: Copying This Manual, Next: Indices, Prev: History, Up: Top
Appendix A Copying This Manual
******************************
* Menu:
* GNU Free Documentation License:: License for copying this manual

File: autoconf.info, Node: GNU Free Documentation License, Up: Copying This Manual
A.1 GNU Free Documentation License
==================================
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it
can be distributed under the terms of this License. Such a notice
grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You
accept the license if you copy, modify or distribute the work in a
way requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could
fall directly within that overall subject. (Thus, if the Document
is in part a textbook of mathematics, a Secondary Section may not
explain any mathematics.) The relationship could be a matter of
historical connection with the subject or with related matters, or
of legal, commercial, philosophical, ethical or political position
regarding them.
The "Invariant Sections" are certain Secondary Sections whose
titles are designated, as being those of Invariant Sections, in
the notice that says that the Document is released under this
License. If a section does not fit the above definition of
Secondary then it is not allowed to be designated as Invariant.
The Document may contain zero Invariant Sections. If the Document
does not identify any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are
listed, as Front-Cover Texts or Back-Cover Texts, in the notice
that says that the Document is released under this License. A
Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images
composed of pixels) generic paint programs or (for drawings) some
widely available drawing editor, and that is suitable for input to
text formatters or for automatic translation to a variety of
formats suitable for input to text formatters. A copy made in an
otherwise Transparent file format whose markup, or absence of
markup, has been arranged to thwart or discourage subsequent
modification by readers is not Transparent. An image format is
not Transparent if used for any substantial amount of text. A
copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available DTD, and
standard-conforming simple HTML, PostScript or PDF designed for
human modification. Examples of transparent image formats include
PNG, XCF and JPG. Opaque formats include proprietary formats that
can be read and edited only by proprietary word processors, SGML or
XML for which the DTD and/or processing tools are not generally
available, and the machine-generated HTML, PostScript or PDF
produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the
material this License requires to appear in the title page. For
works in formats which do not have any title page as such, "Title
Page" means the text near the most prominent appearance of the
work's title, preceding the beginning of the body of the text.
A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
to this definition.
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
this License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow
the conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
Back-Cover Texts on the back cover. Both covers must also clearly
and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the
title equally prominent and visible. You may add other material
on the covers in addition. Copying with changes limited to the
covers, as long as they preserve the title of the Document and
satisfy these conditions, can be treated as verbatim copying in
other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.
If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a
machine-readable Transparent copy along with each Opaque copy, or
state in or with each Opaque copy a computer-network location from
which the general network-using public has access to download
using public-standard network protocols a complete Transparent
copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you
begin distribution of Opaque copies in quantity, to ensure that
this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you
distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of
copies, to give them a chance to provide you with an updated
version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with
the Modified Version filling the role of the Document, thus
licensing distribution and modification of the Modified Version to
whoever possesses a copy of it. In addition, you must do these
things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of
previous versions (which should, if there were any, be listed
in the History section of the Document). You may use the
same title as a previous version if the original publisher of
that version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on
the Title Page. If there is no section Entitled "History" in
the Document, create one stating the title, year, authors,
and publisher of the Document as given on its Title Page,
then add an item describing the Modified Version as stated in
the previous sentence.
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in
the "History" section. You may omit a network location for a
work that was published at least four years before the
Document itself, or if the original publisher of the version
it refers to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the
section all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section
titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this,
add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any
other section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text
has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end
of the list of Cover Texts in the Modified Version. Only one
passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the
Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity
you are acting on behalf of, you may not add another; but you may
replace the old one, on explicit permission from the previous
publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this
License give permission to use their names for publicity for or to
assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination
all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the
documents in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of
that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided for under this License. Any other
attempt to copy, modify, sublicense or distribute the Document is
void, and will automatically terminate your rights under this
License. However, parties who have received copies, or rights,
from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
`http://www.gnu.org/copyleft/'.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If
the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.

File: autoconf.info, Node: Indices, Prev: Copying This Manual, Up: Top
Appendix B Indices
******************
* Menu:
* Environment Variable Index:: Index of environment variables used
* Output Variable Index:: Index of variables set in output files
* Preprocessor Symbol Index:: Index of C preprocessor symbols defined
* Autoconf Macro Index:: Index of Autoconf macros
* M4 Macro Index:: Index of M4, M4sugar, and M4sh macros
* Autotest Macro Index:: Index of Autotest macros
* Program & Function Index:: Index of those with portability problems
* Concept Index:: General index

File: autoconf.info, Node: Environment Variable Index, Next: Output Variable Index, Up: Indices
B.1 Environment Variable Index
==============================
This is an alphabetical list of the environment variables that Autoconf
checks.
[index]
* Menu:
* BIN_SH: Special Shell Variables.
(line 27)
* CDPATH: Special Shell Variables.
(line 31)
* CONFIG_COMMANDS: Obsolete config.status Use.
(line 11)
* CONFIG_FILES: Obsolete config.status Use.
(line 15)
* CONFIG_HEADERS: Obsolete config.status Use.
(line 20)
* CONFIG_LINKS: Obsolete config.status Use.
(line 25)
* CONFIG_SHELL: config.status Invocation.
(line 81)
* CONFIG_SITE: Site Defaults. (line 10)
* CONFIG_STATUS: config.status Invocation.
(line 90)
* DUALCASE: Special Shell Variables.
(line 54)
* ENV: Special Shell Variables.
(line 64)
* IFS: Special Shell Variables.
(line 77)
* LANG: Special Shell Variables.
(line 101)
* LANGUAGE: Special Shell Variables.
(line 110)
* LC_ADDRESS: Special Shell Variables.
(line 120)
* LC_ALL: Special Shell Variables.
(line 101)
* LC_COLLATE: Special Shell Variables.
(line 101)
* LC_CTYPE: Special Shell Variables.
(line 101)
* LC_IDENTIFICATION: Special Shell Variables.
(line 120)
* LC_MEASUREMENT: Special Shell Variables.
(line 120)
* LC_MESSAGES: Special Shell Variables.
(line 101)
* LC_MONETARY: Special Shell Variables.
(line 101)
* LC_NAME: Special Shell Variables.
(line 120)
* LC_NUMERIC: Special Shell Variables.
(line 101)
* LC_PAPER: Special Shell Variables.
(line 120)
* LC_TELEPHONE: Special Shell Variables.
(line 120)
* LC_TIME: Special Shell Variables.
(line 101)
* M4: autom4te Invocation. (line 10)
* MAIL: Special Shell Variables.
(line 64)
* MAILPATH: Special Shell Variables.
(line 64)
* NULLCMD: Special Shell Variables.
(line 201)
* PATH_SEPARATOR: Special Shell Variables.
(line 208)
* PS1: Special Shell Variables.
(line 64)
* PS2: Special Shell Variables.
(line 64)
* PS4: Special Shell Variables.
(line 64)
* PWD: Special Shell Variables.
(line 217)
* SIMPLE_BACKUP_SUFFIX: autoupdate Invocation.
(line 16)
* WARNINGS <1>: autom4te Invocation. (line 58)
* WARNINGS <2>: autoheader Invocation.
(line 77)
* WARNINGS <3>: autoreconf Invocation.
(line 94)
* WARNINGS: autoconf Invocation. (line 63)
* XMKMF: System Services. (line 10)

File: autoconf.info, Node: Output Variable Index, Next: Preprocessor Symbol Index, Prev: Environment Variable Index, Up: Indices
B.2 Output Variable Index
=========================
This is an alphabetical list of the variables that Autoconf can
substitute into files that it creates, typically one or more makefiles.
*Note Setting Output Variables::, for more information on how this is
done.
[index]
* Menu:
* abs_builddir: Preset Output Variables.
(line 143)
* abs_srcdir: Preset Output Variables.
(line 157)
* abs_top_builddir: Preset Output Variables.
(line 150)
* abs_top_srcdir: Preset Output Variables.
(line 164)
* ALLOCA: Particular Functions.
(line 10)
* AWK: Particular Programs. (line 10)
* bindir: Installation Directory Variables.
(line 12)
* build: Canonicalizing. (line 26)
* build_alias: Canonicalizing. (line 9)
* build_cpu: Canonicalizing. (line 26)
* build_os: Canonicalizing. (line 26)
* build_vendor: Canonicalizing. (line 26)
* builddir: Preset Output Variables.
(line 140)
* CC <1>: System Services. (line 49)
* CC: C Compiler. (line 61)
* CFLAGS <1>: C Compiler. (line 61)
* CFLAGS: Preset Output Variables.
(line 15)
* configure_input: Preset Output Variables.
(line 33)
* CPP: C Compiler. (line 98)
* CPPFLAGS: Preset Output Variables.
(line 47)
* cross_compiling: Runtime. (line 56)
* CXX: C++ Compiler. (line 7)
* CXXCPP: C++ Compiler. (line 31)
* CXXFLAGS <1>: C++ Compiler. (line 7)
* CXXFLAGS: Preset Output Variables.
(line 69)
* datadir: Installation Directory Variables.
(line 15)
* datarootdir: Installation Directory Variables.
(line 19)
* DEFS: Preset Output Variables.
(line 73)
* docdir: Installation Directory Variables.
(line 23)
* dvidir: Installation Directory Variables.
(line 27)
* ECHO_C: Preset Output Variables.
(line 83)
* ECHO_N: Preset Output Variables.
(line 83)
* ECHO_T: Preset Output Variables.
(line 83)
* EGREP: Particular Programs. (line 23)
* ERL <1>: Running the Compiler.
(line 23)
* ERL <2>: Language Choice. (line 40)
* ERL: Erlang Compiler and Interpreter.
(line 29)
* ERLANG_INSTALL_LIB_DIR <1>: Erlang Libraries. (line 52)
* ERLANG_INSTALL_LIB_DIR: Installation Directory Variables.
(line 192)
* ERLANG_INSTALL_LIB_DIR_LIBRARY <1>: Erlang Libraries. (line 60)
* ERLANG_INSTALL_LIB_DIR_LIBRARY: Installation Directory Variables.
(line 197)
* ERLANG_LIB_DIR: Erlang Libraries. (line 18)
* ERLANG_LIB_DIR_LIBRARY: Erlang Libraries. (line 26)
* ERLANG_LIB_VER_LIBRARY: Erlang Libraries. (line 26)
* ERLANG_ROOT_DIR: Erlang Libraries. (line 12)
* ERLC <1>: Language Choice. (line 40)
* ERLC: Erlang Compiler and Interpreter.
(line 10)
* ERLCFLAGS <1>: Language Choice. (line 40)
* ERLCFLAGS <2>: Erlang Compiler and Interpreter.
(line 10)
* ERLCFLAGS: Preset Output Variables.
(line 95)
* exec_prefix: Installation Directory Variables.
(line 30)
* EXEEXT <1>: Obsolete Macros. (line 165)
* EXEEXT: Compilers and Preprocessors.
(line 6)
* F77: Fortran Compiler. (line 18)
* FC: Fortran Compiler. (line 39)
* FCFLAGS <1>: Fortran Compiler. (line 39)
* FCFLAGS: Preset Output Variables.
(line 101)
* FCLIBS: Fortran Compiler. (line 79)
* FFLAGS <1>: Fortran Compiler. (line 18)
* FFLAGS: Preset Output Variables.
(line 108)
* FGREP: Particular Programs. (line 28)
* FLIBS: Fortran Compiler. (line 79)
* GETGROUPS_LIBS: Particular Functions.
(line 124)
* GETLOADAVG_LIBS: Particular Functions.
(line 130)
* GREP: Particular Programs. (line 16)
* host: Canonicalizing. (line 34)
* host_alias: Canonicalizing. (line 9)
* host_cpu: Canonicalizing. (line 34)
* host_os: Canonicalizing. (line 34)
* host_vendor: Canonicalizing. (line 34)
* htmldir: Installation Directory Variables.
(line 37)
* includedir: Installation Directory Variables.
(line 40)
* infodir: Installation Directory Variables.
(line 43)
* INSTALL: Particular Programs. (line 33)
* INSTALL_DATA: Particular Programs. (line 33)
* INSTALL_PROGRAM: Particular Programs. (line 33)
* INSTALL_SCRIPT: Particular Programs. (line 33)
* KMEM_GROUP: Particular Functions.
(line 130)
* LDFLAGS: Preset Output Variables.
(line 115)
* LEX: Particular Programs. (line 96)
* LEX_OUTPUT_ROOT: Particular Programs. (line 96)
* LEXLIB: Particular Programs. (line 96)
* libdir: Installation Directory Variables.
(line 46)
* libexecdir: Installation Directory Variables.
(line 49)
* LIBOBJDIR: AC_LIBOBJ vs LIBOBJS.
(line 35)
* LIBOBJS <1>: Particular Structures.
(line 34)
* LIBOBJS <2>: Generic Functions. (line 52)
* LIBOBJS: Particular Functions.
(line 130)
* LIBS <1>: Obsolete Macros. (line 425)
* LIBS <2>: Posix Variants. (line 23)
* LIBS: Preset Output Variables.
(line 129)
* LN_S: Particular Programs. (line 137)
* localedir: Installation Directory Variables.
(line 52)
* localstatedir: Installation Directory Variables.
(line 57)
* mandir: Installation Directory Variables.
(line 60)
* MKDIR_P: Particular Programs. (line 65)
* NEED_SETGID: Particular Functions.
(line 130)
* OBJC: Objective C Compiler.
(line 7)
* OBJCCPP: Objective C Compiler.
(line 26)
* OBJCFLAGS <1>: Objective C Compiler.
(line 7)
* OBJCFLAGS: Preset Output Variables.
(line 136)
* OBJEXT <1>: Obsolete Macros. (line 330)
* OBJEXT: Compilers and Preprocessors.
(line 11)
* oldincludedir: Installation Directory Variables.
(line 63)
* PACKAGE_BUGREPORT: Initializing configure.
(line 44)
* PACKAGE_NAME: Initializing configure.
(line 32)
* PACKAGE_STRING: Initializing configure.
(line 41)
* PACKAGE_TARNAME: Initializing configure.
(line 35)
* PACKAGE_VERSION: Initializing configure.
(line 38)
* pdfdir: Installation Directory Variables.
(line 66)
* POW_LIB: Particular Functions.
(line 338)
* prefix: Installation Directory Variables.
(line 69)
* program_transform_name: Transforming Names. (line 11)
* psdir: Installation Directory Variables.
(line 74)
* RANLIB: Particular Programs. (line 156)
* sbindir: Installation Directory Variables.
(line 77)
* SED: Particular Programs. (line 160)
* SET_MAKE: Output. (line 45)
* sharedstatedir: Installation Directory Variables.
(line 81)
* srcdir: Preset Output Variables.
(line 153)
* subdirs: Subdirectories. (line 12)
* sysconfdir: Installation Directory Variables.
(line 85)
* target: Canonicalizing. (line 41)
* target_alias: Canonicalizing. (line 9)
* target_cpu: Canonicalizing. (line 41)
* target_os: Canonicalizing. (line 41)
* target_vendor: Canonicalizing. (line 41)
* top_builddir: Preset Output Variables.
(line 146)
* top_srcdir: Preset Output Variables.
(line 160)
* X_CFLAGS: System Services. (line 30)
* X_EXTRA_LIBS: System Services. (line 30)
* X_LIBS: System Services. (line 30)
* X_PRE_LIBS: System Services. (line 30)
* YACC: Particular Programs. (line 166)

File: autoconf.info, Node: Preprocessor Symbol Index, Next: Autoconf Macro Index, Prev: Output Variable Index, Up: Indices
B.3 Preprocessor Symbol Index
=============================
This is an alphabetical list of the C preprocessor symbols that the
Autoconf macros define. To work with Autoconf, C source code needs to
use these names in `#if' or `#ifdef' directives.
[index]
* Menu:
* __CHAR_UNSIGNED__: C Compiler. (line 251)
* __EXTENSIONS__: Posix Variants. (line 39)
* __PROTOTYPES: C Compiler. (line 301)
* _ALL_SOURCE: Posix Variants. (line 13)
* _FILE_OFFSET_BITS: System Services. (line 49)
* _GNU_SOURCE: Posix Variants. (line 18)
* _LARGE_FILES: System Services. (line 49)
* _LARGEFILE_SOURCE: Particular Functions.
(line 116)
* _MINIX: Posix Variants. (line 33)
* _POSIX_1_SOURCE: Posix Variants. (line 33)
* _POSIX_PTHREAD_SEMANTICS: Posix Variants. (line 39)
* _POSIX_SOURCE: Posix Variants. (line 33)
* _POSIX_VERSION: Particular Headers. (line 208)
* _TANDEM_SOURCE: Posix Variants. (line 39)
* C_ALLOCA: Particular Functions.
(line 10)
* C_GETLOADAVG: Particular Functions.
(line 130)
* CLOSEDIR_VOID: Particular Functions.
(line 58)
* const: C Compiler. (line 184)
* CXX_NO_MINUS_C_MINUS_O: C++ Compiler. (line 44)
* DGUX: Particular Functions.
(line 130)
* DIRENT: Obsolete Macros. (line 146)
* F77_DUMMY_MAIN: Fortran Compiler. (line 107)
* F77_FUNC: Fortran Compiler. (line 166)
* F77_FUNC_: Fortran Compiler. (line 166)
* F77_MAIN: Fortran Compiler. (line 150)
* F77_NO_MINUS_C_MINUS_O: Fortran Compiler. (line 66)
* FC_FUNC: Fortran Compiler. (line 166)
* FC_FUNC_: Fortran Compiler. (line 166)
* FC_MAIN: Fortran Compiler. (line 150)
* FC_NO_MINUS_C_MINUS_O: Fortran Compiler. (line 66)
* FLEXIBLE_ARRAY_MEMBER: C Compiler. (line 265)
* GETGROUPS_T: Particular Types. (line 14)
* GETLODAVG_PRIVILEGED: Particular Functions.
(line 130)
* GETPGRP_VOID: Particular Functions.
(line 170)
* gid_t: Particular Types. (line 95)
* GWINSZ_IN_SYS_IOCTL: Particular Headers. (line 248)
* HAVE__BOOL: Particular Headers. (line 92)
* HAVE_ALLOCA_H: Particular Functions.
(line 10)
* HAVE_C_VARARRAYS: C Compiler. (line 289)
* HAVE_CONFIG_H: Configuration Headers.
(line 33)
* HAVE_DECL_STRERROR_R: Particular Functions.
(line 321)
* HAVE_DECL_SYMBOL: Generic Declarations.
(line 24)
* HAVE_DIRENT_H: Particular Headers. (line 15)
* HAVE_DOPRNT: Particular Functions.
(line 359)
* HAVE_FUNCTION: Generic Functions. (line 25)
* HAVE_GETMNTENT: Particular Functions.
(line 164)
* HAVE_HEADER: Generic Headers. (line 23)
* HAVE_INT16_T: Particular Types. (line 24)
* HAVE_INT32_T: Particular Types. (line 27)
* HAVE_INT64_T: Particular Types. (line 30)
* HAVE_INT8_T: Particular Types. (line 18)
* HAVE_INTMAX_T: Particular Types. (line 33)
* HAVE_INTPTR_T: Particular Types. (line 38)
* HAVE_LONG_DOUBLE <1>: Obsolete Macros. (line 29)
* HAVE_LONG_DOUBLE: Particular Types. (line 43)
* HAVE_LONG_DOUBLE_WIDER: Particular Types. (line 48)
* HAVE_LONG_FILE_NAMES: System Services. (line 71)
* HAVE_LONG_LONG_INT: Particular Types. (line 53)
* HAVE_LSTAT_EMPTY_STRING_BUG: Particular Functions.
(line 295)
* HAVE_MALLOC: Particular Functions.
(line 203)
* HAVE_MBRTOWC: Particular Functions.
(line 245)
* HAVE_MMAP: Particular Functions.
(line 255)
* HAVE_NDIR_H: Particular Headers. (line 15)
* HAVE_NLIST_H: Particular Functions.
(line 130)
* HAVE_OBSTACK: Particular Functions.
(line 260)
* HAVE_REALLOC: Particular Functions.
(line 264)
* HAVE_RESOLV_H: Particular Headers. (line 63)
* HAVE_RESTARTABLE_SYSCALLS: Obsolete Macros. (line 463)
* HAVE_ST_BLKSIZE: Particular Structures.
(line 26)
* HAVE_ST_BLOCKS: Particular Structures.
(line 34)
* HAVE_ST_RDEV: Particular Structures.
(line 40)
* HAVE_STAT_EMPTY_STRING_BUG: Particular Functions.
(line 295)
* HAVE_STDBOOL_H: Particular Headers. (line 92)
* HAVE_STRCOLL: Particular Functions.
(line 315)
* HAVE_STRERROR_R: Particular Functions.
(line 321)
* HAVE_STRFTIME: Particular Functions.
(line 331)
* HAVE_STRINGIZE: C Compiler. (line 255)
* HAVE_STRNLEN: Particular Functions.
(line 348)
* HAVE_STRUCT_DIRENT_D_INO: Particular Structures.
(line 9)
* HAVE_STRUCT_DIRENT_D_TYPE: Particular Structures.
(line 21)
* HAVE_STRUCT_STAT_ST_BLKSIZE: Particular Structures.
(line 26)
* HAVE_STRUCT_STAT_ST_BLOCKS: Particular Structures.
(line 34)
* HAVE_STRUCT_STAT_ST_RDEV: Particular Structures.
(line 40)
* HAVE_SYS_DIR_H: Particular Headers. (line 15)
* HAVE_SYS_NDIR_H: Particular Headers. (line 15)
* HAVE_SYS_WAIT_H: Particular Headers. (line 187)
* HAVE_TM_ZONE: Particular Structures.
(line 56)
* HAVE_TYPEOF: C Compiler. (line 295)
* HAVE_TZNAME: Particular Structures.
(line 56)
* HAVE_UINT16_T: Particular Types. (line 104)
* HAVE_UINT32_T: Particular Types. (line 108)
* HAVE_UINT64_T: Particular Types. (line 112)
* HAVE_UINT8_T: Particular Types. (line 99)
* HAVE_UINTMAX_T: Particular Types. (line 116)
* HAVE_UINTPTR_T: Particular Types. (line 121)
* HAVE_UNSIGNED_LONG_LONG_INT: Particular Types. (line 126)
* HAVE_UTIME_NULL: Particular Functions.
(line 352)
* HAVE_VFORK_H: Particular Functions.
(line 94)
* HAVE_VPRINTF: Particular Functions.
(line 359)
* HAVE_WAIT3: Obsolete Macros. (line 189)
* HAVE_WORKING_FORK: Particular Functions.
(line 94)
* HAVE_WORKING_VFORK: Particular Functions.
(line 94)
* inline: C Compiler. (line 246)
* int16_t: Particular Types. (line 24)
* int32_t: Particular Types. (line 27)
* int64_t: Particular Types. (line 30)
* int8_t: Particular Types. (line 18)
* INT_16_BITS: Obsolete Macros. (line 242)
* intmax_t: Particular Types. (line 33)
* intptr_t: Particular Types. (line 38)
* LONG_64_BITS: Obsolete Macros. (line 293)
* LSTAT_FOLLOWS_SLASHED_SYMLINK: Particular Functions.
(line 190)
* MAJOR_IN_MKDEV: Particular Headers. (line 58)
* MAJOR_IN_SYSMACROS: Particular Headers. (line 58)
* malloc: Particular Functions.
(line 203)
* mbstate_t: Particular Types. (line 57)
* mode_t: Particular Types. (line 62)
* NDEBUG: Particular Headers. (line 10)
* NDIR: Obsolete Macros. (line 146)
* NEED_MEMORY_H: Obsolete Macros. (line 311)
* NEED_SETGID: Particular Functions.
(line 130)
* NLIST_NAME_UNION: Particular Functions.
(line 130)
* NO_MINUS_C_MINUS_O: C Compiler. (line 90)
* off_t: Particular Types. (line 66)
* PACKAGE_BUGREPORT: Initializing configure.
(line 44)
* PACKAGE_NAME: Initializing configure.
(line 32)
* PACKAGE_STRING: Initializing configure.
(line 41)
* PACKAGE_TARNAME: Initializing configure.
(line 35)
* PACKAGE_VERSION: Initializing configure.
(line 38)
* PARAMS: C Compiler. (line 301)
* pid_t: Particular Types. (line 70)
* PROTOTYPES: C Compiler. (line 301)
* realloc: Particular Functions.
(line 264)
* restrict: C Compiler. (line 212)
* RETSIGTYPE: Particular Types. (line 74)
* SELECT_TYPE_ARG1: Particular Functions.
(line 272)
* SELECT_TYPE_ARG234: Particular Functions.
(line 272)
* SELECT_TYPE_ARG5: Particular Functions.
(line 272)
* SETPGRP_VOID: Particular Functions.
(line 283)
* SETVBUF_REVERSED: Particular Functions.
(line 307)
* size_t: Particular Types. (line 87)
* ssize_t: Particular Types. (line 91)
* STAT_MACROS_BROKEN: Particular Headers. (line 83)
* STDC_HEADERS: Particular Headers. (line 120)
* STRERROR_R_CHAR_P: Particular Functions.
(line 321)
* SVR4: Particular Functions.
(line 130)
* SYS_SIGLIST_DECLARED: Obsolete Macros. (line 132)
* SYSDIR: Obsolete Macros. (line 146)
* SYSNDIR: Obsolete Macros. (line 146)
* TIME_WITH_SYS_TIME: Particular Headers. (line 224)
* TM_IN_SYS_TIME: Particular Structures.
(line 48)
* typeof: C Compiler. (line 295)
* uid_t: Particular Types. (line 95)
* uint16_t: Particular Types. (line 104)
* uint32_t: Particular Types. (line 108)
* uint64_t: Particular Types. (line 112)
* uint8_t: Particular Types. (line 99)
* uintmax_t: Particular Types. (line 116)
* uintptr_t: Particular Types. (line 121)
* UMAX: Particular Functions.
(line 130)
* UMAX4_3: Particular Functions.
(line 130)
* USG: Obsolete Macros. (line 577)
* vfork: Particular Functions.
(line 94)
* volatile: C Compiler. (line 225)
* WORDS_BIGENDIAN: C Compiler. (line 167)
* X_DISPLAY_MISSING: System Services. (line 30)
* YYTEXT_POINTER: Particular Programs. (line 96)

File: autoconf.info, Node: Autoconf Macro Index, Next: M4 Macro Index, Prev: Preprocessor Symbol Index, Up: Indices
B.4 Autoconf Macro Index
========================
This is an alphabetical list of the Autoconf macros.
[index]
* Menu:
* AC_AC_PROG_MKDIR_P: Particular Programs. (line 65)
* AC_AIX: Posix Variants. (line 13)
* AC_ALLOCA: Obsolete Macros. (line 20)
* AC_ARG_ARRAY: Obsolete Macros. (line 23)
* AC_ARG_ENABLE: Package Options. (line 40)
* AC_ARG_PROGRAM: Transforming Names. (line 11)
* AC_ARG_VAR: Setting Output Variables.
(line 71)
* AC_ARG_WITH: External Software. (line 41)
* AC_BEFORE: Suggested Ordering. (line 28)
* AC_C_BIGENDIAN: C Compiler. (line 167)
* AC_C_CHAR_UNSIGNED: C Compiler. (line 251)
* AC_C_CONST: C Compiler. (line 184)
* AC_C_CROSS: Obsolete Macros. (line 26)
* AC_C_FLEXIBLE_ARRAY_MEMBER: C Compiler. (line 265)
* AC_C_INLINE: C Compiler. (line 246)
* AC_C_LONG_DOUBLE: Obsolete Macros. (line 29)
* AC_C_PROTOTYPES: C Compiler. (line 301)
* AC_C_RESTRICT: C Compiler. (line 212)
* AC_C_STRINGIZE: C Compiler. (line 255)
* AC_C_TYPEOF: C Compiler. (line 295)
* AC_C_VARARRAYS: C Compiler. (line 289)
* AC_C_VOLATILE: C Compiler. (line 225)
* AC_CACHE_CHECK: Caching Results. (line 30)
* AC_CACHE_LOAD: Cache Checkpointing. (line 13)
* AC_CACHE_SAVE: Cache Checkpointing. (line 17)
* AC_CACHE_VAL: Caching Results. (line 16)
* AC_CANONICAL_BUILD: Canonicalizing. (line 26)
* AC_CANONICAL_HOST: Canonicalizing. (line 34)
* AC_CANONICAL_SYSTEM: Obsolete Macros. (line 37)
* AC_CANONICAL_TARGET: Canonicalizing. (line 41)
* AC_CHAR_UNSIGNED: Obsolete Macros. (line 47)
* AC_CHECK_ALIGNOF: Generic Compiler Characteristics.
(line 23)
* AC_CHECK_DECL: Generic Declarations.
(line 11)
* AC_CHECK_DECLS: Generic Declarations.
(line 24)
* AC_CHECK_DECLS_ONCE: Generic Declarations.
(line 58)
* AC_CHECK_FILE: Files. (line 13)
* AC_CHECK_FILES: Files. (line 19)
* AC_CHECK_FUNC: Generic Functions. (line 15)
* AC_CHECK_FUNCS: Generic Functions. (line 25)
* AC_CHECK_FUNCS_ONCE: Generic Functions. (line 34)
* AC_CHECK_HEADER: Generic Headers. (line 13)
* AC_CHECK_HEADERS: Generic Headers. (line 23)
* AC_CHECK_HEADERS_ONCE: Generic Headers. (line 60)
* AC_CHECK_LIB: Libraries. (line 11)
* AC_CHECK_MEMBER: Generic Structures. (line 11)
* AC_CHECK_MEMBERS: Generic Structures. (line 25)
* AC_CHECK_PROG: Generic Programs. (line 23)
* AC_CHECK_PROGS: Generic Programs. (line 33)
* AC_CHECK_SIZEOF: Generic Compiler Characteristics.
(line 8)
* AC_CHECK_TARGET_TOOL: Generic Programs. (line 43)
* AC_CHECK_TARGET_TOOLS: Generic Programs. (line 75)
* AC_CHECK_TOOL: Generic Programs. (line 59)
* AC_CHECK_TOOLS: Generic Programs. (line 88)
* AC_CHECK_TYPE <1>: Obsolete Macros. (line 50)
* AC_CHECK_TYPE: Generic Types. (line 11)
* AC_CHECK_TYPES: Generic Types. (line 16)
* AC_CHECKING: Obsolete Macros. (line 97)
* AC_COMPILE_CHECK: Obsolete Macros. (line 101)
* AC_COMPILE_IFELSE: Running the Compiler.
(line 13)
* AC_COMPUTE_INT: Generic Compiler Characteristics.
(line 30)
* AC_CONFIG_AUX_DIR: Input. (line 20)
* AC_CONFIG_COMMANDS: Configuration Commands.
(line 13)
* AC_CONFIG_COMMANDS_POST: Configuration Commands.
(line 41)
* AC_CONFIG_COMMANDS_PRE: Configuration Commands.
(line 35)
* AC_CONFIG_FILES: Configuration Files. (line 9)
* AC_CONFIG_HEADERS: Configuration Headers.
(line 33)
* AC_CONFIG_LIBOBJ_DIR: Generic Functions. (line 93)
* AC_CONFIG_LINKS: Configuration Links. (line 12)
* AC_CONFIG_MACRO_DIR: Input. (line 48)
* AC_CONFIG_SRCDIR: Input. (line 7)
* AC_CONFIG_SUBDIRS: Subdirectories. (line 12)
* AC_CONFIG_TESTDIR: Making testsuite Scripts.
(line 37)
* AC_CONST: Obsolete Macros. (line 109)
* AC_COPYRIGHT: Notices. (line 21)
* AC_CROSS_CHECK: Obsolete Macros. (line 112)
* AC_CYGWIN: Obsolete Macros. (line 116)
* AC_DATAROOTDIR_CHECKED: Changed Directory Variables.
(line 58)
* AC_DECL_SYS_SIGLIST: Obsolete Macros. (line 132)
* AC_DECL_YYTEXT: Obsolete Macros. (line 143)
* AC_DEFINE: Defining Symbols. (line 32)
* AC_DEFINE_UNQUOTED: Defining Symbols. (line 55)
* AC_DEFUN: Macro Definitions. (line 6)
* AC_DEFUN_ONCE: One-Shot Macros. (line 14)
* AC_DIAGNOSE: Reporting Messages. (line 11)
* AC_DIR_HEADER: Obsolete Macros. (line 146)
* AC_DYNIX_SEQ: Obsolete Macros. (line 157)
* AC_EGREP_CPP: Running the Preprocessor.
(line 73)
* AC_EGREP_HEADER: Running the Preprocessor.
(line 66)
* AC_EMXOS2: Obsolete Macros. (line 170)
* AC_ENABLE: Package Options. (line 61)
* AC_ERLANG_CHECK_LIB: Erlang Libraries. (line 26)
* AC_ERLANG_NEED_ERL: Erlang Compiler and Interpreter.
(line 41)
* AC_ERLANG_NEED_ERLC: Erlang Compiler and Interpreter.
(line 24)
* AC_ERLANG_PATH_ERL: Erlang Compiler and Interpreter.
(line 29)
* AC_ERLANG_PATH_ERLC: Erlang Compiler and Interpreter.
(line 10)
* AC_ERLANG_SUBST_INSTALL_LIB_DIR <1>: Erlang Libraries. (line 52)
* AC_ERLANG_SUBST_INSTALL_LIB_DIR: Installation Directory Variables.
(line 192)
* AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR <1>: Erlang Libraries. (line 60)
* AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR: Installation Directory Variables.
(line 197)
* AC_ERLANG_SUBST_LIB_DIR: Erlang Libraries. (line 18)
* AC_ERLANG_SUBST_ROOT_DIR: Erlang Libraries. (line 12)
* AC_ERROR: Obsolete Macros. (line 174)
* AC_EXEEXT: Obsolete Macros. (line 165)
* AC_F77_DUMMY_MAIN: Fortran Compiler. (line 107)
* AC_F77_FUNC: Fortran Compiler. (line 226)
* AC_F77_LIBRARY_LDFLAGS: Fortran Compiler. (line 79)
* AC_F77_MAIN: Fortran Compiler. (line 150)
* AC_F77_WRAPPERS: Fortran Compiler. (line 166)
* AC_FATAL: Reporting Messages. (line 33)
* AC_FC_FREEFORM: Fortran Compiler. (line 275)
* AC_FC_FUNC: Fortran Compiler. (line 226)
* AC_FC_LIBRARY_LDFLAGS: Fortran Compiler. (line 79)
* AC_FC_MAIN: Fortran Compiler. (line 150)
* AC_FC_SRCEXT: Fortran Compiler. (line 236)
* AC_FC_WRAPPERS: Fortran Compiler. (line 166)
* AC_FIND_X: Obsolete Macros. (line 177)
* AC_FIND_XTRA: Obsolete Macros. (line 180)
* AC_FOREACH: Obsolete Macros. (line 183)
* AC_FUNC_ALLOCA: Particular Functions.
(line 10)
* AC_FUNC_CHECK: Obsolete Macros. (line 186)
* AC_FUNC_CHOWN: Particular Functions.
(line 54)
* AC_FUNC_CLOSEDIR_VOID: Particular Functions.
(line 58)
* AC_FUNC_ERROR_AT_LINE: Particular Functions.
(line 70)
* AC_FUNC_FNMATCH: Particular Functions.
(line 74)
* AC_FUNC_FNMATCH_GNU: Particular Functions.
(line 86)
* AC_FUNC_FORK: Particular Functions.
(line 94)
* AC_FUNC_FSEEKO: Particular Functions.
(line 116)
* AC_FUNC_GETGROUPS: Particular Functions.
(line 124)
* AC_FUNC_GETLOADAVG: Particular Functions.
(line 130)
* AC_FUNC_GETMNTENT: Particular Functions.
(line 164)
* AC_FUNC_GETPGRP: Particular Functions.
(line 170)
* AC_FUNC_LSTAT: Particular Functions.
(line 295)
* AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK: Particular Functions.
(line 190)
* AC_FUNC_MALLOC: Particular Functions.
(line 203)
* AC_FUNC_MBRTOWC: Particular Functions.
(line 245)
* AC_FUNC_MEMCMP: Particular Functions.
(line 235)
* AC_FUNC_MKTIME: Particular Functions.
(line 249)
* AC_FUNC_MMAP: Particular Functions.
(line 255)
* AC_FUNC_OBSTACK: Particular Functions.
(line 260)
* AC_FUNC_REALLOC: Particular Functions.
(line 264)
* AC_FUNC_SELECT_ARGTYPES: Particular Functions.
(line 272)
* AC_FUNC_SETPGRP: Particular Functions.
(line 283)
* AC_FUNC_SETVBUF_REVERSED: Particular Functions.
(line 307)
* AC_FUNC_STAT: Particular Functions.
(line 295)
* AC_FUNC_STRCOLL: Particular Functions.
(line 315)
* AC_FUNC_STRERROR_R: Particular Functions.
(line 321)
* AC_FUNC_STRFTIME: Particular Functions.
(line 331)
* AC_FUNC_STRNLEN: Particular Functions.
(line 348)
* AC_FUNC_STRTOD: Particular Functions.
(line 338)
* AC_FUNC_STRTOLD: Particular Functions.
(line 344)
* AC_FUNC_UTIME_NULL: Particular Functions.
(line 352)
* AC_FUNC_VPRINTF: Particular Functions.
(line 359)
* AC_FUNC_WAIT3: Obsolete Macros. (line 189)
* AC_GCC_TRADITIONAL: Obsolete Macros. (line 197)
* AC_GETGROUPS_T: Obsolete Macros. (line 200)
* AC_GETLOADAVG: Obsolete Macros. (line 203)
* AC_GNU_SOURCE: Posix Variants. (line 18)
* AC_HAVE_C_BACKSLASH_A: C Compiler. (line 159)
* AC_HAVE_FUNCS: Obsolete Macros. (line 206)
* AC_HAVE_HEADERS: Obsolete Macros. (line 209)
* AC_HAVE_LIBRARY: Obsolete Macros. (line 213)
* AC_HAVE_POUNDBANG: Obsolete Macros. (line 220)
* AC_HEADER_ASSERT: Particular Headers. (line 10)
* AC_HEADER_CHECK: Obsolete Macros. (line 223)
* AC_HEADER_DIRENT: Particular Headers. (line 15)
* AC_HEADER_EGREP: Obsolete Macros. (line 226)
* AC_HEADER_MAJOR: Particular Headers. (line 58)
* AC_HEADER_RESOLV: Particular Headers. (line 63)
* AC_HEADER_STAT: Particular Headers. (line 83)
* AC_HEADER_STDBOOL: Particular Headers. (line 92)
* AC_HEADER_STDC: Particular Headers. (line 120)
* AC_HEADER_SYS_WAIT: Particular Headers. (line 187)
* AC_HEADER_TIME: Particular Headers. (line 224)
* AC_HEADER_TIOCGWINSZ: Particular Headers. (line 248)
* AC_HELP_STRING <1>: Obsolete Macros. (line 229)
* AC_HELP_STRING: Pretty Help Strings. (line 14)
* AC_INCLUDES_DEFAULT: Default Includes. (line 29)
* AC_INIT <1>: Obsolete Macros. (line 232)
* AC_INIT: Initializing configure.
(line 10)
* AC_INLINE: Obsolete Macros. (line 239)
* AC_INT_16_BITS: Obsolete Macros. (line 242)
* AC_IRIX_SUN: Obsolete Macros. (line 246)
* AC_ISC_POSIX: Posix Variants. (line 23)
* AC_LANG_ASSERT: Language Choice. (line 69)
* AC_LANG_C: Obsolete Macros. (line 260)
* AC_LANG_CALL: Generating Sources. (line 115)
* AC_LANG_CONFTEST: Generating Sources. (line 12)
* AC_LANG_CPLUSPLUS: Obsolete Macros. (line 263)
* AC_LANG_FORTRAN77: Obsolete Macros. (line 266)
* AC_LANG_FUNC_LINK_TRY: Generating Sources. (line 127)
* AC_LANG_POP: Language Choice. (line 56)
* AC_LANG_PROGRAM: Generating Sources. (line 53)
* AC_LANG_PUSH: Language Choice. (line 51)
* AC_LANG_RESTORE: Obsolete Macros. (line 269)
* AC_LANG_SAVE: Obsolete Macros. (line 274)
* AC_LANG_SOURCE: Generating Sources. (line 21)
* AC_LANG_WERROR: Generic Compiler Characteristics.
(line 42)
* AC_LIBOBJ: Generic Functions. (line 52)
* AC_LIBSOURCE: Generic Functions. (line 61)
* AC_LIBSOURCES: Generic Functions. (line 85)
* AC_LINK_FILES: Obsolete Macros. (line 278)
* AC_LINK_IFELSE: Running the Linker. (line 24)
* AC_LN_S: Obsolete Macros. (line 290)
* AC_LONG_64_BITS: Obsolete Macros. (line 293)
* AC_LONG_DOUBLE: Obsolete Macros. (line 297)
* AC_LONG_FILE_NAMES: Obsolete Macros. (line 305)
* AC_MAJOR_HEADER: Obsolete Macros. (line 308)
* AC_MEMORY_H: Obsolete Macros. (line 311)
* AC_MINGW32: Obsolete Macros. (line 317)
* AC_MINIX: Posix Variants. (line 33)
* AC_MINUS_C_MINUS_O: Obsolete Macros. (line 321)
* AC_MMAP: Obsolete Macros. (line 324)
* AC_MODE_T: Obsolete Macros. (line 327)
* AC_MSG_CHECKING: Printing Messages. (line 24)
* AC_MSG_ERROR: Printing Messages. (line 56)
* AC_MSG_FAILURE: Printing Messages. (line 66)
* AC_MSG_NOTICE: Printing Messages. (line 46)
* AC_MSG_RESULT: Printing Messages. (line 35)
* AC_MSG_WARN: Printing Messages. (line 72)
* AC_OBJEXT: Obsolete Macros. (line 330)
* AC_OBSOLETE: Obsolete Macros. (line 336)
* AC_OFF_T: Obsolete Macros. (line 351)
* AC_OUTPUT <1>: Obsolete Macros. (line 354)
* AC_OUTPUT: Output. (line 13)
* AC_OUTPUT_COMMANDS: Obsolete Macros. (line 363)
* AC_PACKAGE_BUGREPORT: Initializing configure.
(line 44)
* AC_PACKAGE_NAME: Initializing configure.
(line 32)
* AC_PACKAGE_STRING: Initializing configure.
(line 41)
* AC_PACKAGE_TARNAME: Initializing configure.
(line 35)
* AC_PACKAGE_VERSION: Initializing configure.
(line 38)
* AC_PATH_PROG: Generic Programs. (line 103)
* AC_PATH_PROGS: Generic Programs. (line 108)
* AC_PATH_TARGET_TOOL: Generic Programs. (line 113)
* AC_PATH_TOOL: Generic Programs. (line 118)
* AC_PATH_X: System Services. (line 10)
* AC_PATH_XTRA: System Services. (line 30)
* AC_PID_T: Obsolete Macros. (line 392)
* AC_PREFIX: Obsolete Macros. (line 395)
* AC_PREFIX_DEFAULT: Default Prefix. (line 16)
* AC_PREFIX_PROGRAM: Default Prefix. (line 25)
* AC_PREPROC_IFELSE: Running the Preprocessor.
(line 20)
* AC_PREREQ: Notices. (line 10)
* AC_PRESERVE_HELP_ORDER: Help Formatting. (line 20)
* AC_PROG_AWK: Particular Programs. (line 10)
* AC_PROG_CC: C Compiler. (line 61)
* AC_PROG_CC_C89: C Compiler. (line 132)
* AC_PROG_CC_C99: C Compiler. (line 145)
* AC_PROG_CC_C_O: C Compiler. (line 90)
* AC_PROG_CC_STDC: C Compiler. (line 122)
* AC_PROG_CPP: C Compiler. (line 98)
* AC_PROG_CPP_WERROR: C Compiler. (line 111)
* AC_PROG_CXX: C++ Compiler. (line 7)
* AC_PROG_CXX_C_O: C++ Compiler. (line 44)
* AC_PROG_CXXCPP: C++ Compiler. (line 31)
* AC_PROG_EGREP: Particular Programs. (line 23)
* AC_PROG_F77: Fortran Compiler. (line 18)
* AC_PROG_F77_C_O: Fortran Compiler. (line 66)
* AC_PROG_FC: Fortran Compiler. (line 39)
* AC_PROG_FC_C_O: Fortran Compiler. (line 66)
* AC_PROG_FGREP: Particular Programs. (line 28)
* AC_PROG_GCC_TRADITIONAL: C Compiler. (line 311)
* AC_PROG_GREP: Particular Programs. (line 16)
* AC_PROG_INSTALL: Particular Programs. (line 33)
* AC_PROG_LEX: Particular Programs. (line 96)
* AC_PROG_LN_S: Particular Programs. (line 137)
* AC_PROG_MAKE_SET: Output. (line 45)
* AC_PROG_OBJC: Objective C Compiler.
(line 7)
* AC_PROG_OBJCCPP: Objective C Compiler.
(line 26)
* AC_PROG_RANLIB: Particular Programs. (line 156)
* AC_PROG_SED: Particular Programs. (line 160)
* AC_PROG_YACC: Particular Programs. (line 166)
* AC_PROGRAM_CHECK: Obsolete Macros. (line 404)
* AC_PROGRAM_EGREP: Obsolete Macros. (line 407)
* AC_PROGRAM_PATH: Obsolete Macros. (line 410)
* AC_PROGRAMS_CHECK: Obsolete Macros. (line 398)
* AC_PROGRAMS_PATH: Obsolete Macros. (line 401)
* AC_REMOTE_TAPE: Obsolete Macros. (line 413)
* AC_REPLACE_FNMATCH: Particular Functions.
(line 368)
* AC_REPLACE_FUNCS: Generic Functions. (line 113)
* AC_REQUIRE: Prerequisite Macros. (line 17)
* AC_REQUIRE_AUX_FILE: Input. (line 37)
* AC_REQUIRE_CPP: Language Choice. (line 84)
* AC_RESTARTABLE_SYSCALLS: Obsolete Macros. (line 416)
* AC_RETSIGTYPE: Obsolete Macros. (line 419)
* AC_REVISION: Notices. (line 29)
* AC_RSH: Obsolete Macros. (line 422)
* AC_RUN_IFELSE: Runtime. (line 20)
* AC_SCO_INTL: Obsolete Macros. (line 425)
* AC_SEARCH_LIBS: Libraries. (line 49)
* AC_SET_MAKE: Obsolete Macros. (line 436)
* AC_SETVBUF_REVERSED: Obsolete Macros. (line 433)
* AC_SIZE_T: Obsolete Macros. (line 442)
* AC_SIZEOF_TYPE: Obsolete Macros. (line 439)
* AC_ST_BLKSIZE: Obsolete Macros. (line 454)
* AC_ST_BLOCKS: Obsolete Macros. (line 457)
* AC_ST_RDEV: Obsolete Macros. (line 460)
* AC_STAT_MACROS_BROKEN: Obsolete Macros. (line 445)
* AC_STDC_HEADERS: Obsolete Macros. (line 448)
* AC_STRCOLL: Obsolete Macros. (line 451)
* AC_STRUCT_DIRENT_D_INO: Particular Structures.
(line 9)
* AC_STRUCT_DIRENT_D_TYPE: Particular Structures.
(line 21)
* AC_STRUCT_ST_BLKSIZE: Particular Structures.
(line 26)
* AC_STRUCT_ST_BLOCKS: Particular Structures.
(line 34)
* AC_STRUCT_ST_RDEV: Particular Structures.
(line 40)
* AC_STRUCT_TIMEZONE: Particular Structures.
(line 56)
* AC_STRUCT_TM: Particular Structures.
(line 48)
* AC_SUBST: Setting Output Variables.
(line 13)
* AC_SUBST_FILE: Setting Output Variables.
(line 30)
* AC_SYS_INTERPRETER: System Services. (line 42)
* AC_SYS_LARGEFILE: System Services. (line 49)
* AC_SYS_LONG_FILE_NAMES: System Services. (line 71)
* AC_SYS_POSIX_TERMIOS: System Services. (line 75)
* AC_SYS_RESTARTABLE_SYSCALLS: Obsolete Macros. (line 463)
* AC_SYS_SIGLIST_DECLARED: Obsolete Macros. (line 478)
* AC_TEST_CPP: Obsolete Macros. (line 481)
* AC_TEST_PROGRAM: Obsolete Macros. (line 484)
* AC_TIME_WITH_SYS_TIME: Obsolete Macros. (line 490)
* AC_TIMEZONE: Obsolete Macros. (line 487)
* AC_TRY_COMPILE: Obsolete Macros. (line 494)
* AC_TRY_CPP: Obsolete Macros. (line 513)
* AC_TRY_LINK: Obsolete Macros. (line 526)
* AC_TRY_LINK_FUNC: Obsolete Macros. (line 555)
* AC_TRY_RUN: Obsolete Macros. (line 560)
* AC_TYPE_GETGROUPS: Particular Types. (line 14)
* AC_TYPE_INT16_T: Particular Types. (line 24)
* AC_TYPE_INT32_T: Particular Types. (line 27)
* AC_TYPE_INT64_T: Particular Types. (line 30)
* AC_TYPE_INT8_T: Particular Types. (line 18)
* AC_TYPE_INTMAX_T: Particular Types. (line 33)
* AC_TYPE_INTPTR_T: Particular Types. (line 38)
* AC_TYPE_LONG_DOUBLE: Particular Types. (line 43)
* AC_TYPE_LONG_DOUBLE_WIDER: Particular Types. (line 48)
* AC_TYPE_LONG_LONG_INT: Particular Types. (line 53)
* AC_TYPE_MBSTATE_T: Particular Types. (line 57)
* AC_TYPE_MODE_T: Particular Types. (line 62)
* AC_TYPE_OFF_T: Particular Types. (line 66)
* AC_TYPE_PID_T: Particular Types. (line 70)
* AC_TYPE_SIGNAL: Particular Types. (line 74)
* AC_TYPE_SIZE_T: Particular Types. (line 87)
* AC_TYPE_SSIZE_T: Particular Types. (line 91)
* AC_TYPE_UID_T: Particular Types. (line 95)
* AC_TYPE_UINT16_T: Particular Types. (line 104)
* AC_TYPE_UINT32_T: Particular Types. (line 108)
* AC_TYPE_UINT64_T: Particular Types. (line 112)
* AC_TYPE_UINT8_T: Particular Types. (line 99)
* AC_TYPE_UINTMAX_T: Particular Types. (line 116)
* AC_TYPE_UINTPTR_T: Particular Types. (line 121)
* AC_TYPE_UNSIGNED_LONG_LONG_INT: Particular Types. (line 126)
* AC_UID_T: Obsolete Macros. (line 571)
* AC_UNISTD_H: Obsolete Macros. (line 574)
* AC_USE_SYSTEM_EXTENSIONS: Posix Variants. (line 39)
* AC_USG: Obsolete Macros. (line 577)
* AC_UTIME_NULL: Obsolete Macros. (line 582)
* AC_VALIDATE_CACHED_SYSTEM_TUPLE: Obsolete Macros. (line 585)
* AC_VERBOSE: Obsolete Macros. (line 590)
* AC_VFORK: Obsolete Macros. (line 593)
* AC_VPRINTF: Obsolete Macros. (line 596)
* AC_WAIT3: Obsolete Macros. (line 599)
* AC_WARN: Obsolete Macros. (line 602)
* AC_WARNING: Reporting Messages. (line 29)
* AC_WITH: External Software. (line 141)
* AC_WORDS_BIGENDIAN: Obsolete Macros. (line 605)
* AC_XENIX_DIR: Obsolete Macros. (line 608)
* AC_YYTEXT_POINTER: Obsolete Macros. (line 623)
* AH_BOTTOM: Autoheader Macros. (line 50)
* AH_HEADER: Configuration Headers.
(line 56)
* AH_TEMPLATE: Autoheader Macros. (line 19)
* AH_TOP: Autoheader Macros. (line 47)
* AH_VERBATIM: Autoheader Macros. (line 40)
* AU_ALIAS: Obsoleting Macros. (line 34)
* AU_DEFUN: Obsoleting Macros. (line 18)

File: autoconf.info, Node: M4 Macro Index, Next: Autotest Macro Index, Prev: Autoconf Macro Index, Up: Indices
B.5 M4 Macro Index
==================
This is an alphabetical list of the M4, M4sugar, and M4sh macros.
[index]
* Menu:
* AS_BOURNE_COMPATIBLE: Programming in M4sh. (line 26)
* AS_CASE: Programming in M4sh. (line 32)
* AS_DIRNAME: Programming in M4sh. (line 37)
* AS_IF: Programming in M4sh. (line 42)
* AS_MESSAGE_FD: File Descriptor Macros.
(line 17)
* AS_MESSAGE_LOG_FD: File Descriptor Macros.
(line 27)
* AS_MKDIR_P: Programming in M4sh. (line 56)
* AS_ORIGINAL_STDIN_FD: File Descriptor Macros.
(line 33)
* AS_SET_CATFILE: Programming in M4sh. (line 91)
* AS_SHELL_SANITIZE: Programming in M4sh. (line 67)
* AS_TR_CPP: Programming in M4sh. (line 74)
* AS_TR_SH: Programming in M4sh. (line 82)
* m4_append: Text processing Macros.
(line 31)
* m4_append_uniq: Text processing Macros.
(line 31)
* m4_bpatsubst: Redefined M4 Macros. (line 32)
* m4_bregexp: Redefined M4 Macros. (line 41)
* m4_builtin: Redefined M4 Macros. (line 6)
* m4_decr: Redefined M4 Macros. (line 6)
* m4_define: Redefined M4 Macros. (line 6)
* m4_defn: Redefined M4 Macros. (line 16)
* m4_dnl: Redefined M4 Macros. (line 13)
* m4_dquote: Evaluation Macros. (line 11)
* m4_dumpdef: Redefined M4 Macros. (line 6)
* m4_errprint: Redefined M4 Macros. (line 6)
* m4_esyscmd: Redefined M4 Macros. (line 6)
* m4_eval: Redefined M4 Macros. (line 6)
* m4_exit: Redefined M4 Macros. (line 20)
* m4_for: Looping constructs. (line 9)
* m4_foreach: Looping constructs. (line 16)
* m4_foreach_w: Looping constructs. (line 25)
* m4_format: Redefined M4 Macros. (line 6)
* m4_if: Redefined M4 Macros. (line 25)
* m4_ifdef: Redefined M4 Macros. (line 6)
* m4_include: Redefined M4 Macros. (line 29)
* m4_incr: Redefined M4 Macros. (line 6)
* m4_index: Redefined M4 Macros. (line 6)
* m4_indir: Redefined M4 Macros. (line 6)
* m4_len: Redefined M4 Macros. (line 6)
* m4_maketemp: Redefined M4 Macros. (line 77)
* m4_mkstemp: Redefined M4 Macros. (line 77)
* m4_normalize: Text processing Macros.
(line 25)
* m4_pattern_allow: Forbidden Patterns. (line 28)
* m4_pattern_forbid: Forbidden Patterns. (line 15)
* m4_popdef: Redefined M4 Macros. (line 37)
* m4_pushdef: Redefined M4 Macros. (line 6)
* m4_quote: Evaluation Macros. (line 14)
* m4_re_escape: Text processing Macros.
(line 10)
* m4_shift: Redefined M4 Macros. (line 6)
* m4_sinclude: Redefined M4 Macros. (line 29)
* m4_split: Text processing Macros.
(line 19)
* m4_substr: Redefined M4 Macros. (line 6)
* m4_syscmd: Redefined M4 Macros. (line 6)
* m4_sysval: Redefined M4 Macros. (line 6)
* m4_tolower: Text processing Macros.
(line 15)
* m4_toupper: Text processing Macros.
(line 15)
* m4_translit: Redefined M4 Macros. (line 6)
* m4_undefine: Redefined M4 Macros. (line 6)
* m4_wrap: Redefined M4 Macros. (line 46)

File: autoconf.info, Node: Autotest Macro Index, Next: Program & Function Index, Prev: M4 Macro Index, Up: Indices
B.6 Autotest Macro Index
========================
This is an alphabetical list of the Autotest macros.
[index]
* Menu:
* AT_CAPTURE_FILE: Writing testsuite.at. (line 63)
* AT_CHECK: Writing testsuite.at. (line 87)
* AT_CLEANUP: Writing testsuite.at. (line 76)
* AT_COPYRIGHT: Writing testsuite.at. (line 22)
* AT_DATA: Writing testsuite.at. (line 80)
* AT_INIT: Writing testsuite.at. (line 16)
* AT_KEYWORDS: Writing testsuite.at. (line 51)
* AT_SETUP: Writing testsuite.at. (line 45)
* AT_TESTED: Writing testsuite.at. (line 30)
* AT_XFAIL_IF: Writing testsuite.at. (line 68)

File: autoconf.info, Node: Program & Function Index, Next: Concept Index, Prev: Autotest Macro Index, Up: Indices
B.7 Program and Function Index
==============================
This is an alphabetical list of the programs and functions which
portability is discussed in this document.
[index]
* Menu:
* !: Limitations of Builtins.
(line 23)
* .: Limitations of Builtins.
(line 16)
* /usr/bin/ksh on Solaris: Shellology. (line 63)
* /usr/dt/bin/dtksh on Solaris: Shellology. (line 66)
* /usr/xpg4/bin/sh on Solaris: Shellology. (line 64)
* alloca: Particular Functions.
(line 10)
* alloca.h: Particular Functions.
(line 10)
* assert.h: Particular Headers. (line 10)
* Awk: Limitations of Usual Tools.
(line 10)
* basename: Limitations of Usual Tools.
(line 90)
* break: Limitations of Builtins.
(line 42)
* case: Limitations of Builtins.
(line 45)
* cat: Limitations of Usual Tools.
(line 94)
* cc: Limitations of Usual Tools.
(line 97)
* cd: Limitations of Builtins.
(line 104)
* chmod: Limitations of Usual Tools.
(line 130)
* chown: Particular Functions.
(line 54)
* closedir: Particular Functions.
(line 58)
* cmp: Limitations of Usual Tools.
(line 140)
* cp: Limitations of Usual Tools.
(line 147)
* ctype.h: Particular Headers. (line 120)
* date: Limitations of Usual Tools.
(line 199)
* diff: Limitations of Usual Tools.
(line 209)
* dirent.h: Particular Headers. (line 15)
* dirname: Limitations of Usual Tools.
(line 215)
* echo: Limitations of Builtins.
(line 124)
* egrep: Limitations of Usual Tools.
(line 222)
* error_at_line: Particular Functions.
(line 70)
* eval: Limitations of Builtins.
(line 150)
* exit <1>: Limitations of Builtins.
(line 194)
* exit: Function Portability.
(line 12)
* export: Limitations of Builtins.
(line 219)
* expr: Limitations of Usual Tools.
(line 246)
* expr (|): Limitations of Usual Tools.
(line 252)
* false: Limitations of Builtins.
(line 245)
* fgrep: Limitations of Usual Tools.
(line 343)
* find: Limitations of Usual Tools.
(line 350)
* float.h: Particular Headers. (line 120)
* fnmatch: Particular Functions.
(line 74)
* fnmatch.h: Particular Functions.
(line 368)
* for: Limitations of Builtins.
(line 249)
* fork: Particular Functions.
(line 94)
* free: Function Portability.
(line 22)
* fseeko: Particular Functions.
(line 116)
* getgroups: Particular Functions.
(line 124)
* getloadavg: Particular Functions.
(line 130)
* getmntent: Particular Functions.
(line 164)
* getpgid: Particular Functions.
(line 170)
* getpgrp: Particular Functions.
(line 170)
* grep: Limitations of Usual Tools.
(line 364)
* if: Limitations of Builtins.
(line 275)
* inttypes.h <1>: Particular Types. (line 6)
* inttypes.h: Header Portability. (line 16)
* isinf: Function Portability.
(line 27)
* isnan: Function Portability.
(line 27)
* join: Limitations of Usual Tools.
(line 414)
* ksh: Shellology. (line 57)
* ksh88: Shellology. (line 57)
* ksh93: Shellology. (line 57)
* linux/irda.h: Header Portability. (line 23)
* linux/random.h: Header Portability. (line 26)
* ln: Limitations of Usual Tools.
(line 427)
* ls: Limitations of Usual Tools.
(line 439)
* lstat: Particular Functions.
(line 190)
* make: Portable Make. (line 6)
* malloc <1>: Particular Functions.
(line 203)
* malloc: Function Portability.
(line 73)
* mbrtowc: Particular Functions.
(line 245)
* memcmp: Particular Functions.
(line 235)
* mkdir: Limitations of Usual Tools.
(line 451)
* mktemp: Limitations of Usual Tools.
(line 484)
* mktime: Particular Functions.
(line 249)
* mmap: Particular Functions.
(line 255)
* mv: Limitations of Usual Tools.
(line 508)
* ndir.h: Particular Headers. (line 15)
* net/if.h: Header Portability. (line 29)
* netinet/if_ether.h: Header Portability. (line 49)
* nlist.h: Particular Functions.
(line 147)
* od: Limitations of Usual Tools.
(line 540)
* pdksh: Shellology. (line 77)
* printf: Limitations of Builtins.
(line 304)
* putenv: Function Portability.
(line 80)
* pwd: Limitations of Builtins.
(line 317)
* read: Limitations of Builtins.
(line 314)
* realloc <1>: Particular Functions.
(line 264)
* realloc: Function Portability.
(line 96)
* resolv.h: Particular Headers. (line 63)
* rm: Limitations of Usual Tools.
(line 549)
* sed: Limitations of Usual Tools.
(line 566)
* sed (t): Limitations of Usual Tools.
(line 693)
* select: Particular Functions.
(line 272)
* set: Limitations of Builtins.
(line 348)
* setpgrp: Particular Functions.
(line 283)
* setvbuf: Particular Functions.
(line 307)
* shift: Limitations of Builtins.
(line 402)
* signal: Function Portability.
(line 101)
* signal.h: Particular Types. (line 74)
* snprintf: Function Portability.
(line 112)
* source: Limitations of Builtins.
(line 410)
* sprintf: Function Portability.
(line 123)
* sscanf: Function Portability.
(line 129)
* stat: Particular Functions.
(line 295)
* stdarg.h: Particular Headers. (line 120)
* stdbool.h: Particular Headers. (line 92)
* stdint.h <1>: Particular Types. (line 6)
* stdint.h: Header Portability. (line 16)
* stdlib.h <1>: Particular Types. (line 6)
* stdlib.h <2>: Particular Headers. (line 120)
* stdlib.h: Header Portability. (line 72)
* strcoll: Particular Functions.
(line 315)
* strerror_r <1>: Particular Functions.
(line 321)
* strerror_r: Function Portability.
(line 137)
* strftime: Particular Functions.
(line 331)
* string.h: Particular Headers. (line 120)
* strings.h: Particular Headers. (line 137)
* strnlen <1>: Particular Functions.
(line 348)
* strnlen: Function Portability.
(line 143)
* strtod: Particular Functions.
(line 338)
* strtold: Particular Functions.
(line 344)
* sys/dir.h: Particular Headers. (line 15)
* sys/ioctl.h: Particular Headers. (line 248)
* sys/mkdev.h: Particular Headers. (line 58)
* sys/mount.h: Header Portability. (line 75)
* sys/ndir.h: Particular Headers. (line 15)
* sys/ptem.h: Header Portability. (line 79)
* sys/socket.h: Header Portability. (line 82)
* sys/stat.h: Particular Headers. (line 83)
* sys/sysmacros.h: Particular Headers. (line 58)
* sys/time.h <1>: Particular Structures.
(line 48)
* sys/time.h: Particular Headers. (line 224)
* sys/types.h: Particular Types. (line 6)
* sys/ucred.h: Header Portability. (line 85)
* sys/wait.h: Particular Headers. (line 187)
* sysconf: Function Portability.
(line 158)
* system.h: Particular Headers. (line 92)
* termios.h: Particular Headers. (line 248)
* test: Limitations of Builtins.
(line 414)
* time.h <1>: Particular Structures.
(line 48)
* time.h: Particular Headers. (line 224)
* touch: Limitations of Usual Tools.
(line 753)
* trap: Limitations of Builtins.
(line 499)
* true: Limitations of Builtins.
(line 548)
* unistd.h: Particular Headers. (line 208)
* unlink: Function Portability.
(line 162)
* unset: Limitations of Builtins.
(line 559)
* unsetenv: Function Portability.
(line 168)
* utime: Particular Functions.
(line 352)
* va_copy: Function Portability.
(line 173)
* va_list: Function Portability.
(line 180)
* vfork: Particular Functions.
(line 94)
* vfork.h: Particular Functions.
(line 94)
* vprintf: Particular Functions.
(line 359)
* vsnprintf: Function Portability.
(line 112)
* vsprintf: Function Portability.
(line 123)
* wchar.h: Particular Types. (line 57)
* X11/extensions/scrnsaver.h: Header Portability. (line 88)

File: autoconf.info, Node: Concept Index, Prev: Program & Function Index, Up: Indices
B.8 Concept Index
=================
This is an alphabetical list of the files, tools, and concepts
introduced in this document.
[index]
* Menu:
* "$@": Shell Substitutions. (line 31)
* $(COMMANDS): Shell Substitutions. (line 195)
* $<, explicit rules, and VPATH: $< in Explicit Rules.
(line 6)
* ${VAR=EXPANDED-VALUE}: Shell Substitutions. (line 120)
* ${VAR=LITERAL}: Shell Substitutions. (line 90)
* @&t@: Quadrigraphs. (line 6)
* @S|@: Quadrigraphs. (line 6)
* ^ quoting: Shell Substitutions. (line 228)
* _m4_divert_diversion: New Macros. (line 6)
* `COMMANDS`: Shell Substitutions. (line 166)
* acconfig.h: acconfig.h. (line 6)
* aclocal.m4: Making configure Scripts.
(line 6)
* Ash: Shellology. (line 16)
* autoconf: autoconf Invocation. (line 6)
* Autoconf upgrading <1>: Autoconf 2.13. (line 6)
* Autoconf upgrading: Autoconf 1. (line 6)
* autoheader: autoheader Invocation.
(line 6)
* Autoheader macros: Autoheader Macros. (line 6)
* Autom4te Library: autom4te Invocation. (line 225)
* autom4te.cache: autom4te Invocation. (line 130)
* autom4te.cfg: autom4te Invocation. (line 259)
* Automake: Automake. (line 19)
* Automatic remaking: Automatic Remaking. (line 6)
* automatic rule rewriting and VPATH: Automatic Rule Rewriting.
(line 6)
* autopoint: autoreconf Invocation.
(line 27)
* autoreconf: autoreconf Invocation.
(line 6)
* autoscan: autoscan Invocation. (line 6)
* Autotest: Using Autotest. (line 6)
* AUTOTEST_PATH: testsuite Invocation.
(line 36)
* autoupdate: autoupdate Invocation.
(line 6)
* Back trace <1>: autom4te Invocation. (line 86)
* Back trace: autoconf Invocation. (line 88)
* Bash: Shellology. (line 43)
* Bash 2.05 and later: Shellology. (line 49)
* Bootstrap: Bootstrapping. (line 6)
* BSD make and obj/: obj/ and Make. (line 6)
* buffer overruns: Buffer Overruns. (line 6)
* Build directories: Build Directories. (line 6)
* C function portability: Function Portability.
(line 6)
* C types: Types. (line 6)
* Cache: Caching Results. (line 6)
* Cache variable: Cache Variable Names.
(line 6)
* Cache, enabling: configure Invocation.
(line 18)
* Canonical system type: Canonicalizing. (line 6)
* changequote: Changequote is Evil. (line 6)
* Coding style: Coding Style. (line 6)
* Command Substitution: Shell Substitutions. (line 166)
* Commands for configuration: Configuration Commands.
(line 6)
* Comments in Makefile rules: Comments in Make Rules.
(line 6)
* Common autoconf behavior: Common Behavior. (line 6)
* Compilers: Compilers and Preprocessors.
(line 6)
* config.h: Configuration Headers.
(line 6)
* config.h.bot: acconfig.h. (line 6)
* config.h.in: Header Templates. (line 6)
* config.h.top: acconfig.h. (line 6)
* config.status: config.status Invocation.
(line 6)
* config.sub: Specifying Names. (line 61)
* Configuration actions: Configuration Actions.
(line 6)
* Configuration commands: Configuration Commands.
(line 6)
* Configuration file creation: Configuration Files. (line 6)
* Configuration Header: Configuration Headers.
(line 6)
* Configuration Header Template: Header Templates. (line 6)
* Configuration links: Configuration Links. (line 6)
* configure <1>: Running configure Scripts.
(line 6)
* configure: Making configure Scripts.
(line 6)
* Configure subdirectories: Subdirectories. (line 6)
* configure.ac: Making configure Scripts.
(line 27)
* configure.in: Making configure Scripts.
(line 27)
* Copyright Notice <1>: Writing testsuite.at.
(line 22)
* Copyright Notice: Notices. (line 21)
* Creating configuration files: Configuration Files. (line 6)
* Creating temporary files: Limitations of Usual Tools.
(line 484)
* Cross compilation: Hosts and Cross-Compilation.
(line 6)
* Darwin: Systemology. (line 23)
* datarootdir: Changed Directory Variables.
(line 6)
* Declaration, checking: Declarations. (line 6)
* Default includes: Default Includes. (line 6)
* Dependencies between macros: Dependencies Between Macros.
(line 6)
* Descriptors: File Descriptors. (line 6)
* descriptors: File Descriptor Macros.
(line 6)
* Directories, build: Build Directories. (line 6)
* Directories, installation: Installation Directory Variables.
(line 6)
* dnl <1>: Coding Style. (line 40)
* dnl: Macro Definitions. (line 37)
* double-colon rules and VPATH: VPATH and Double-colon.
(line 6)
* Endianness: C Compiler. (line 167)
* Erlang: Erlang Compiler and Interpreter.
(line 6)
* Erlang, Library, checking: Erlang Libraries. (line 6)
* exiting portably: Exiting Portably. (line 6)
* explicit rules, $<, and VPATH: $< in Explicit Rules.
(line 6)
* External software: External Software. (line 6)
* F77: Fortran Compiler. (line 6)
* FDL, GNU Free Documentation License: GNU Free Documentation License.
(line 6)
* File descriptors: File Descriptors. (line 6)
* file descriptors: File Descriptor Macros.
(line 6)
* File system conventions: File System Conventions.
(line 6)
* File, checking: Files. (line 6)
* floating point: Floating Point Portability.
(line 6)
* Forbidden patterns: Forbidden Patterns. (line 6)
* Fortran: Fortran Compiler. (line 6)
* Function, checking: Particular Functions.
(line 6)
* Gettext: autoreconf Invocation.
(line 27)
* GNU build system: The GNU Build System.
(line 6)
* Gnulib: Gnulib. (line 11)
* Header portability: Header Portability. (line 6)
* Header templates: Header Templates. (line 6)
* Header, checking: Header Files. (line 6)
* Help strings: Pretty Help Strings. (line 6)
* Here-documents: Here-Documents. (line 6)
* History of autoconf: History. (line 6)
* ifnames: ifnames Invocation. (line 6)
* Imake: Why Not Imake. (line 6)
* Includes, default: Default Includes. (line 6)
* input: File Descriptor Macros.
(line 6)
* Install prefix: Default Prefix. (line 6)
* Installation directories: Installation Directory Variables.
(line 6)
* Instantiation: Output. (line 13)
* Introduction: Introduction. (line 6)
* Korn shell: Shellology. (line 57)
* Ksh: Shellology. (line 57)
* Language: Language Choice. (line 6)
* Large file support: System Services. (line 49)
* LFS: System Services. (line 49)
* Library, checking: Libraries. (line 6)
* Libtool: Libtool. (line 14)
* License <1>: Copying This Manual. (line 6)
* License: Distributing. (line 6)
* Limitations of make: Portable Make. (line 6)
* Limitations of shell builtins: Limitations of Builtins.
(line 6)
* Limitations of usual tools: Limitations of Usual Tools.
(line 6)
* Links: Configuration Links. (line 12)
* Links for configuration: Configuration Links. (line 6)
* Listing directories: Limitations of Usual Tools.
(line 439)
* low-level output: File Descriptor Macros.
(line 6)
* M4: Programming in M4. (line 6)
* M4 quotation: M4 Quotation. (line 6)
* M4sugar: Programming in M4sugar.
(line 6)
* Macro invocation stack <1>: autom4te Invocation. (line 86)
* Macro invocation stack: autoconf Invocation. (line 88)
* Macros, called once: One-Shot Macros. (line 6)
* Macros, obsoleting: Obsoleting Macros. (line 6)
* Macros, ordering: Suggested Ordering. (line 6)
* Macros, prerequisites: Prerequisite Macros. (line 6)
* make -k: make -k Status. (line 6)
* make and MAKEFLAGS: The Make Macro MAKEFLAGS.
(line 6)
* make and SHELL: The Make Macro SHELL.
(line 6)
* Makefile rules and comments: Comments in Make Rules.
(line 6)
* Makefile substitutions: Makefile Substitutions.
(line 6)
* MAKEFLAGS and make: The Make Macro MAKEFLAGS.
(line 6)
* Making directories: Limitations of Usual Tools.
(line 451)
* Messages, from autoconf: Reporting Messages. (line 6)
* Messages, from configure: Printing Messages. (line 6)
* Moving open files: Limitations of Usual Tools.
(line 508)
* Notices in configure: Notices. (line 6)
* null pointers: Null Pointers. (line 6)
* obj/, subdirectory: obj/ and Make. (line 6)
* Obsolete constructs: Obsolete Constructs. (line 6)
* Obsoleting macros: Obsoleting Macros. (line 6)
* obstack: Particular Functions.
(line 260)
* One-shot macros: One-Shot Macros. (line 6)
* Options, package: Package Options. (line 6)
* Ordering macros: Suggested Ordering. (line 6)
* Output variables <1>: Setting Output Variables.
(line 6)
* Output variables: Preset Output Variables.
(line 6)
* Output variables, special characters in: Special Chars in Variables.
(line 6)
* output, low-level: File Descriptor Macros.
(line 6)
* Outputting files: Output. (line 6)
* overflow, arithmetic: Integer Overflow. (line 6)
* Package options: Package Options. (line 6)
* package.m4: Making testsuite Scripts.
(line 12)
* Patterns, forbidden: Forbidden Patterns. (line 6)
* portability: Varieties of Unportability.
(line 6)
* Portability of C functions: Function Portability.
(line 6)
* Portability of headers: Header Portability. (line 6)
* Portable C and C++ programming: Portable C and C++. (line 6)
* Portable shell programming: Portable Shell. (line 6)
* positional parameters: Shell Substitutions. (line 77)
* Posix termios headers: System Services. (line 75)
* Precious Variable: Setting Output Variables.
(line 57)
* Prefix for install: Default Prefix. (line 6)
* Preprocessors: Compilers and Preprocessors.
(line 6)
* prerequisite directories and VPATH: Tru64 Directory Magic.
(line 6)
* Prerequisite macros: Prerequisite Macros. (line 6)
* Program names, transforming: Transforming Names. (line 6)
* Programs, checking: Alternative Programs.
(line 6)
* QNX 4.25: Systemology. (line 37)
* quadrigraphs: Quadrigraphs. (line 6)
* quotation <1>: M4 Quotation. (line 6)
* quotation: Autoconf Language. (line 6)
* Remaking automatically: Automatic Remaking. (line 6)
* Revision: Notices. (line 29)
* Rule, Single Suffix Inference: Single Suffix Rules. (line 6)
* Separated Dependencies: Single Suffix Rules. (line 9)
* SHELL and make: The Make Macro SHELL.
(line 6)
* Shell assignments: Assignments. (line 6)
* Shell builtins: Limitations of Builtins.
(line 6)
* Shell file descriptors: File Descriptors. (line 6)
* Shell here-documents: Here-Documents. (line 6)
* Shell parentheses: Parentheses. (line 6)
* Shell slashes: Slashes. (line 6)
* Shell substitutions: Shell Substitutions. (line 6)
* Shell variables: Special Shell Variables.
(line 6)
* Shellology: Shellology. (line 6)
* Single Suffix Inference Rule: Single Suffix Rules. (line 6)
* Site defaults: Site Defaults. (line 6)
* Site details: Site Details. (line 6)
* Special shell variables: Special Shell Variables.
(line 6)
* standard input: File Descriptor Macros.
(line 6)
* Standard symbols: Standard Symbols. (line 6)
* Structure, checking: Structures. (line 6)
* Subdirectory configure: Subdirectories. (line 6)
* Substitutions in makefiles: Makefile Substitutions.
(line 6)
* Symbolic links: Limitations of Usual Tools.
(line 427)
* System type <1>: Canonicalizing. (line 6)
* System type: Specifying Names. (line 6)
* Systemology: Systemology. (line 6)
* termios Posix headers: System Services. (line 75)
* test group: testsuite Scripts. (line 12)
* testsuite <1>: testsuite Invocation.
(line 6)
* testsuite: testsuite Scripts. (line 6)
* timestamp resolution <1>: Timestamps and Make. (line 6)
* timestamp resolution: Limitations of Usual Tools.
(line 162)
* Transforming program names: Transforming Names. (line 6)
* Tru64: Systemology. (line 44)
* Types: Types. (line 6)
* undefined macro: New Macros. (line 6)
* Unix version 7: Systemology. (line 49)
* Upgrading autoconf <1>: Autoconf 2.13. (line 6)
* Upgrading autoconf: Autoconf 1. (line 6)
* V7: Systemology. (line 49)
* Variable, Precious: Setting Output Variables.
(line 57)
* Version: Notices. (line 10)
* volatile objects: Volatile Objects. (line 6)
* VPATH: VPATH and Make. (line 6)
* VPATH and automatic rule rewriting: Automatic Rule Rewriting.
(line 6)
* VPATH and double-colon rules: VPATH and Double-colon.
(line 6)
* VPATH and prerequisite directories: Tru64 Directory Magic.
(line 6)
* VPATH, explicit rules, and $<: $< in Explicit Rules.
(line 6)
* VPATH, resolving target pathnames: Make Target Lookup. (line 6)
* X Window System: System Services. (line 10)
* Zsh: Shellology. (line 97)

Tag Table:
Node: Top2270
Node: Introduction19833
Node: The GNU Build System24874
Node: Automake25853
Node: Gnulib27803
Node: Libtool29112
Node: Pointers30534
Ref: Pointers-Footnote-131827
Node: Making configure Scripts31987
Node: Writing configure.ac35022
Node: Shell Script Compiler36457
Node: Autoconf Language38725
Node: configure.ac Layout44596
Node: autoscan Invocation46000
Node: ifnames Invocation48504
Node: autoconf Invocation49704
Node: autoreconf Invocation55030
Node: Setup59466
Node: Initializing configure60725
Node: Notices62902
Node: Input64554
Node: Output67279
Node: Configuration Actions69757
Node: Configuration Files74567
Node: Makefile Substitutions76047
Node: Preset Output Variables77789
Node: Installation Directory Variables84957
Node: Changed Directory Variables92349
Node: Build Directories94943
Node: Automatic Remaking96582
Node: Configuration Headers98741
Node: Header Templates102174
Node: autoheader Invocation103693
Node: Autoheader Macros106966
Node: Configuration Commands109231
Node: Configuration Links111025
Node: Subdirectories112449
Node: Default Prefix114901
Node: Existing Tests116323
Node: Common Behavior118125
Node: Standard Symbols118764
Node: Default Includes119345
Node: Alternative Programs121599
Node: Particular Programs122285
Node: Generic Programs130301
Node: Files136583
Node: Libraries137477
Node: Library Functions140785
Node: Function Portability141408
Node: Particular Functions150318
Node: Generic Functions166484
Node: Header Files172125
Node: Header Portability172758
Node: Particular Headers175627
Node: Generic Headers185565
Node: Declarations188596
Node: Particular Declarations189192
Node: Generic Declarations189416
Node: Structures192323
Node: Particular Structures192938
Node: Generic Structures195650
Node: Types197129
Node: Particular Types197649
Node: Generic Types202125
Node: Compilers and Preprocessors203544
Node: Specific Compiler Characteristics204736
Node: Generic Compiler Characteristics205841
Node: C Compiler208126
Node: C++ Compiler222144
Node: Objective C Compiler224343
Node: Erlang Compiler and Interpreter225728
Node: Fortran Compiler227731
Node: System Services242043
Node: Posix Variants245617
Node: Erlang Libraries247573
Node: Writing Tests251027
Node: Language Choice253051
Ref: Language Choice-Footnote-1256818
Node: Writing Test Programs256974
Node: Guidelines257552
Node: Test Functions259811
Node: Generating Sources261209
Node: Running the Preprocessor265888
Node: Running the Compiler269198
Node: Running the Linker270516
Node: Runtime272428
Node: Systemology276589
Node: Multiple Cases278938
Node: Results280521
Node: Defining Symbols281340
Node: Setting Output Variables285284
Node: Special Chars in Variables290583
Node: Caching Results291843
Node: Cache Variable Names295557
Node: Cache Files297119
Node: Cache Checkpointing299097
Node: Printing Messages300471
Node: Programming in M4304063
Node: M4 Quotation304934
Node: Active Characters305779
Ref: Active Characters-Footnote-1307135
Node: One Macro Call307157
Node: Quotation and Nested Macros308797
Node: Changequote is Evil311764
Node: Quadrigraphs314291
Node: Quotation Rule Of Thumb316344
Node: Using autom4te319233
Ref: Using autom4te-Footnote-1319884
Node: autom4te Invocation319933
Node: Customizing autom4te328439
Node: Programming in M4sugar329721
Node: Redefined M4 Macros330435
Node: Looping constructs333743
Node: Evaluation Macros334880
Node: Text processing Macros336182
Node: Forbidden Patterns337667
Node: Programming in M4sh339038
Node: File Descriptor Macros342954
Node: Writing Autoconf Macros345041
Node: Macro Definitions345842
Node: Macro Names347618
Node: Reporting Messages350203
Node: Dependencies Between Macros351560
Node: Prerequisite Macros352253
Node: Suggested Ordering355323
Node: One-Shot Macros356864
Node: Obsoleting Macros357788
Node: Coding Style359569
Node: Portable Shell367124
Node: Shellology369684
Node: Here-Documents375016
Node: File Descriptors377665
Node: File System Conventions381241
Node: Shell Substitutions387019
Node: Assignments395084
Node: Parentheses396973
Node: Slashes397786
Node: Special Shell Variables398638
Node: Limitations of Builtins407394
Node: Limitations of Usual Tools430255
Node: Portable Make461576
Node: $< in Ordinary Make Rules462907
Node: Failure in Make Rules463373
Node: Special Chars in Names464454
Node: Backslash-Newline-Newline465428
Node: Backslash-Newline Comments466055
Node: Long Lines in Makefiles466946
Node: Macros and Submakes467322
Node: The Make Macro MAKEFLAGS469432
Node: The Make Macro SHELL470317
Node: Comments in Make Rules472048
Node: obj/ and Make472534
Node: make -k Status473173
Node: VPATH and Make473795
Node: VPATH and Double-colon475046
Node: $< in Explicit Rules475418
Node: Automatic Rule Rewriting475885
Node: Tru64 Directory Magic481813
Node: Make Target Lookup482639
Node: Single Suffix Rules487081
Node: Timestamps and Make488427
Node: Portable C and C++489641
Node: Varieties of Unportability491224
Node: Integer Overflow493321
Node: Null Pointers494684
Node: Buffer Overruns495311
Node: Volatile Objects498100
Node: Floating Point Portability503778
Node: Exiting Portably504285
Node: Manual Configuration505761
Node: Specifying Names506594
Node: Canonicalizing509636
Node: Using System Type511893
Node: Site Configuration514704
Node: Help Formatting515600
Node: External Software516544
Node: Package Options522908
Node: Pretty Help Strings525964
Node: Site Details527784
Node: Transforming Names529017
Node: Transformation Options530099
Node: Transformation Examples530576
Node: Transformation Rules532297
Node: Site Defaults533843
Node: Running configure Scripts537764
Node: Basic Installation538778
Node: Compilers and Options541636
Node: Multiple Architectures542290
Node: Installation Names543178
Node: Optional Features544401
Node: System Type545185
Node: Sharing Defaults546507
Node: Defining Variables547145
Node: configure Invocation548037
Node: config.status Invocation549166
Node: Obsolete Constructs553411
Node: Obsolete config.status Use554363
Node: acconfig.h556136
Node: autoupdate Invocation558153
Node: Obsolete Macros559844
Node: Autoconf 1579801
Node: Changed File Names580867
Node: Changed Makefiles581617
Node: Changed Macros582705
Node: Changed Results583959
Node: Changed Macro Writing586079
Node: Autoconf 2.13587359
Node: Changed Quotation588568
Node: New Macros590486
Node: Hosts and Cross-Compilation592281
Node: AC_LIBOBJ vs LIBOBJS596580
Node: AC_FOO_IFELSE vs AC_TRY_FOO598195
Node: Using Autotest600198
Node: Using an Autotest Test Suite602639
Node: testsuite Scripts602932
Node: Autotest Logs607350
Node: Writing testsuite.at609693
Node: testsuite Invocation614559
Node: Making testsuite Scripts617991
Node: FAQ621979
Node: Distributing622720
Node: Why GNU M4623769
Node: Bootstrapping624638
Node: Why Not Imake625248
Node: Defining Directories629993
Node: autom4te.cache632040
Node: Present But Cannot Be Compiled633881
Node: History637734
Node: Genesis638521
Node: Exodus639699
Node: Leviticus642744
Node: Numbers644272
Node: Deuteronomy646187
Node: Copying This Manual648858
Node: GNU Free Documentation License649092
Node: Indices671492
Node: Environment Variable Index672132
Node: Output Variable Index677916
Node: Preprocessor Symbol Index692806
Node: Autoconf Macro Index709264
Node: M4 Macro Index741563
Node: Autotest Macro Index746693
Node: Program & Function Index747672
Node: Concept Index766346

End Tag Table
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