Previous: Build Directories, Up: Makefile Substitutions

4.7.5 Automatic Remaking

You can put rules like the following in the top-level for a package to automatically update the configuration information when you change the configuration files. This example includes all of the optional files, such as aclocal.m4 and those related to configuration header files. Omit from the rules for any of these files that your package does not use.

The ‘$(srcdir)/’ prefix is included because of limitations in the VPATH mechanism.

The stamp- files are necessary because the timestamps of and config.h are not changed if remaking them does not change their contents. This feature avoids unnecessary recompilation. You should include the file your package's distribution, so that make considers up to date. Don't use touch (see Limitations of Usual Tools); instead, use echo (using date would cause needless differences, hence CVS conflicts, etc.).

     $(srcdir)/configure: aclocal.m4
             cd '$(srcdir)' && autoconf
     # autoheader might not change, so touch a stamp file.
     $(srcdir)/ aclocal.m4
             cd '$(srcdir)' && autoheader
             echo timestamp > '$(srcdir)/'
     config.h: stamp-h
     stamp-h: config.status
     Makefile: config.status
     config.status: configure
             ./config.status --recheck

(Be careful if you copy these lines directly into your makefile, as you need to convert the indented lines to start with the tab character.)

In addition, you should use

     AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h])

so config.status ensures that config.h is considered up to date. See Output, for more information about AC_OUTPUT.

See config.status Invocation, for more examples of handling configuration-related dependencies.