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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 @option{-}, 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 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:

@option{--help}

@option{-h}

Print a summary of the command line options and exit.

@option{--version}

@option{-V}

Print the version number of Autoconf and exit.

@option{--verbose}

@option{-v}

Report processing steps.

@option{--debug}

@option{-d}

Don't remove the temporary files.

@option{--autoconf-dir=dir}

@option{-A dir}

Override the location where the installed Autoconf data files are looked for. You can also set the AC_MACRODIR environment variable to a directory; this option overrides the environment variable. This option is rarely needed and dangerous; it is only used when one plays with different versions of Autoconf simultaneously.

@option{--localdir=dir}

@option{-l dir}

Look for the package file `aclocal.m4' in directory dir instead of in the current directory.

@option{--output=file}

@option{-o file}

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

@option{--warnings=category}

@option{-W category}

Report the warnings related to category (which can actually be a comma separated list). See section 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. @command{autoconf -W category} will actually behave as if you had run:

autoconf --warnings=syntax,$WARNINGS,category

If you want to disable @command{autoconf}'s defaults and WARNINGS, but (for example) enable the warnings about obsolete constructs, you would use @option{-W none,obsolete}. @command{autoconf} displays a back trace for errors, but not for warnings; if you want them, just pass @option{-W error}. For instance, on this `configure.ac':

AC_DEFUN([INNER],
[AC_TRY_RUN([true])])

AC_DEFUN([OUTER],
[INNER])

AC_INIT
OUTER

you get:

$ autoconf -Wcross
configure.ac:8: warning: AC_TRY_RUN called without default \
to allow cross compiling
$ autoconf -Wcross,error
configure.ac:8: error: AC_TRY_RUN called without default \
to allow cross compiling
acgeneral.m4:3044: AC_TRY_RUN is expanded from...
configure.ac:2: INNER is expanded from...
configure.ac:5: OUTER is expanded from...
configure.ac:8: the top level

@option{--trace=macro[:format]}

@option{-t macro[:format]}

Do not create the configure script, but list the calls to macro according to the format. Multiple @option{--trace} arguments can be used to list several macros. Multiple @option{--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 below for details on the format.

@option{--initialization}

@option{-i}

By default, @option{--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 @option{--trace} to scan `configure.ac'.

The format of @option{--trace} can use the following special escapes:

`$$'

The character `$'.

`$f'

The filename 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.

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 its 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

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