File: autoconf.info,  Node: Writing Autoconf Input,  Next: autoscan Invocation,  Up: Making configure Scripts

3.1 Writing ‘configure.ac’
==========================

To produce a ‘configure’ script for a software package, create a file
called ‘configure.ac’ that contains invocations of the Autoconf macros
that test the system features your package needs or can use.  Autoconf
macros already exist to check for many features; see *note Existing
Tests::, for their descriptions.  For most other features, you can use
Autoconf template macros to produce custom checks; see *note Writing
Tests::, for information about them.  For especially tricky or
specialized features, ‘configure.ac’ might need to contain some
hand-crafted shell commands; see *note Portable Shell Programming:
Portable Shell.  The ‘autoscan’ program can give you a good start in
writing ‘configure.ac’ (*note autoscan Invocation::, for more
information).

   Previous versions of Autoconf promoted the name ‘configure.in’, which
is somewhat ambiguous (the tool needed to process this file is not
described by its extension), and introduces a slight confusion with
‘config.h.in’ and so on (for which ‘.in’ means "to be processed by
‘configure’").  Using ‘configure.ac’ is now preferred, while the use of
‘configure.in’ will cause warnings from ‘autoconf’.

* Menu:

* Shell Script Compiler::       Autoconf as solution of a problem
* Autoconf Language::           Programming in Autoconf
* Autoconf Input Layout::       Standard organization of ‘configure.ac’