3. Making configure Scripts

The configuration scripts that Autoconf produces are by convention called configure. When run, configure creates several files, replacing configuration parameters in them with appropriate values. The files that configure creates are:

• - one or more ‘Makefile’ files, usually one in each subdirectory of the package (see section Substitutions in Makefiles);
• - optionally, a C header file, the name of which is configurable, containing #define directives (see section Configuration Header Files);
• - a shell script called ‘config.status’ that, when run, recreates the files listed above (see section config.status Invocation);
• - an optional shell script normally called ‘config.cache’ (created when using ‘configure --config-cache’) that saves the results of running many of the tests (see section Cache Files);
• - a file called ‘config.log’ containing any messages produced by compilers, to help debugging if configure makes a mistake.

To create a configure script with Autoconf, you need to write an Autoconf input file ‘configure.ac’ (or ‘configure.in’) and run autoconf on it. If you write your own feature tests to supplement those that come with Autoconf, you might also write files called ‘aclocal.m4’ and ‘acsite.m4’. If you use a C header file to contain #define directives, you might also run autoheader, and you can distribute the generated file ‘config.h.in’ with the package.

Here is a diagram showing how the files that can be used in configuration are produced. Programs that are executed are suffixed by ‘*’. Optional files are enclosed in square brackets (‘[]’). autoconf and autoheader also read the installed Autoconf macro files (by reading ‘autoconf.m4’).

Files used in preparing a software package for distribution:

your source files --> [autoscan*] --> [configure.scan] --> configure.ac

configure.ac --.
               |   .------> autoconf* -----> configure
[aclocal.m4] --+---+
               |   `-----> [autoheader*] --> [config.h.in]
[acsite.m4] ---'

Makefile.in -------------------------------> Makefile.in

Files used in configuring a software package:

                       .-------------> [config.cache]
configure* ------------+-------------> config.log
                       |
[config.h.in] -.       v            .-> [config.h] -.
               +--> config.status* -+               +--> make*
Makefile.in ---'                    `-> Makefile ---'