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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 (see section 9. 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 section 9.3 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. Passing `-W category' will actually behave 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'. See section 8.2.1 Invoking autom4te, 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 8.2.1 Invoking autom4te, 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 `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
More traces deleted

The example below highlights the difference between `$@', `$*', and $%.

$ cat configure.ac
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"} = "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:${|:::::|}*'
More traces deleted

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