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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:

`--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.

`--autoconf-dir=dir'
`-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.

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

`--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 section 9.3 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([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

`--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


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