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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 -, 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 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

Also look for input files in dir. Multiple invocations accumulate. Directories are browsed from last to first.

--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). See 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. autoconf -W category will actually behave as if you had run:

autoconf --warnings=syntax,$WARNINGS,category

If you want to disable autoconf's defaults and WARNINGS, but (for example) enable the warnings about obsolete constructs, you would use -W none,obsolete.

autoconf displays a back trace for errors, but not for warnings; if you want them, just pass -W error. For instance, on this configure.ac:

AC_DEFUN([INNER],
[AC_TRY_RUN([exit (0)])])

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

--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 below 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.

The format of --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