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16.2 autoconf Invocation

Usually run by autoreconf. You may want to run autoconf when your project does not use Automake.

To create configure from, run the autoconf program with no arguments. autoconf processes with the M4 macro processor, using the Autoconf macros. If you give autoconf an argument, it reads that file instead of 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 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 (see 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:


Print a summary of the command line options and exit.


Print the version number of Autoconf and exit.


Report processing steps.


Don’t remove the temporary files.


Remake configure even if newer than its input files.

-I dir

Append dir to the include path. Multiple invocations accumulate.

-B dir

Prepend dir to the include path. Multiple invocations accumulate.

-o file

Save output (script or trace) to file. The file - stands for the standard output.

-W category

Report the warnings related to category (which can actually be a comma separated list). See Reporting Messages, macro AC_DIAGNOSE, for a comprehensive list of categories. Special values include:


report all the warnings


report none


treats warnings as errors


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. To disable the defaults and WARNINGS, and then enable warnings about obsolete constructs, 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. See autom4te Invocation for some examples.

-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 autom4te Invocation, for details on the format.


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 file, but parsing it yourself is extremely fragile and error-prone. It is suggested that you rely upon --trace to scan For instance, to find the list of variables that are substituted, use:

$ autoconf -t AC_SUBST
More traces deleted

The example below highlights the difference between ‘$@’, ‘$*’, and ‘$%’.

$ cat
AC_DEFINE(This, is, [an
$ autoconf -t 'AC_DEFINE:@: $@
*: $*
%: $%'
@: [This],[is],[an
*: This,is,an
%: 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"} = "";
$ac_subst{"ECHO_N"} = "";
$ac_subst{"ECHO_T"} = "";
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:${|:::::|}*'
More traces deleted

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