Editing Autoconf (section)

== Behavior ==
Autoconf generates a <code>configure</code> script based on the contents of a <code>configure.ac</code> file, which characterizes a particular body of source code.  The <code>configure</code> script, when run, scans the build environment and generates a subordinate <code>config.status</code> script which, in turn, converts other input files and most commonly <code>Makefile.in</code> into output files (<code>Makefile</code>), which are appropriate for that build environment.  Finally, the <code>make</code> program uses <code>Makefile</code> to generate executable programs from source code.

The complexity of Autotools reflects the variety of circumstances under which a body of source code may be built.

* If a source code file is changed then it suffices to re-run <code>make</code>, which only re-compiles that part of the body of the source code affected by the change.
* If a <code>.in</code> file has changed then it suffices to re-run <code>config.status</code> and <code>make</code>.
* If the body of source code is copied to another computer then it is sufficient to re-run <code>configure</code> (which runs <code>config.status</code>) and <code>make</code>.  (For this reason source code using Autotools is normally distributed without the files that <code>configure</code> generates.)
* If the body of source code is changed more fundamentally, then <code>configure.ac</code> and the <code>.in</code> files need to be changed and all subsequent steps also followed.

To process files, autoconf uses the GNU implementation of the [[m4 (computer language)|m4]] macro system.

Autoconf comes with several auxiliary programs such as <code>autoheader</code>, which is used to help manage [[C (programming language)|C]] [[header file]]s; <code>autoscan</code>, which can create an initial input file for Autoconf; and <code>ifnames</code>, which can list C pre-processor identifiers used in the program.