(autoconf.info)Versioning


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4.2 Dealing with Autoconf versions
==================================

The following optional macros can be used to help choose the minimum
version of Autoconf that can successfully compile a given
`configure.ac'.

 -- Macro: AC_PREREQ (VERSION)
     Ensure that a recent enough version of Autoconf is being used.  If
     the version of Autoconf being used to create `configure' is
     earlier than VERSION, print an error message to the standard error
     output and exit with failure (exit status is 63).  For example:

          AC_PREREQ([2.62])

     This macro is the only macro that may be used before `AC_INIT', but
     for consistency, you are invited not to do so.

 -- Macro: AC_AUTOCONF_VERSION
     This macro was introduced in Autoconf 2.62.  It identifies the
     version of Autoconf that is currently parsing the input file, in a
     format suitable for `m4_version_compare' (*note
     m4_version_compare::); in other words, for this release of
     Autoconf, its value is `2.62'.  One potential use of this macro is
     for writing conditional fallbacks based on when a feature was
     added to Autoconf, rather than using `AC_PREREQ' to require the
     newer version of Autoconf.  However, remember that the Autoconf
     philosophy favors feature checks over version checks.


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