4.8 Substitutions in Makefiles

Each subdirectory in a distribution that contains something to be compiled or installed should come with a file Makefile.in, from which configure creates a file Makefile in that directory. To create Makefile, configure performs a simple variable substitution, replacing occurrences of ‘@variable@’ in Makefile.in with the value that configure has determined for that variable. Variables that are substituted into output files in this way are called output variables. They are ordinary shell variables that are set in configure. To make configure substitute a particular variable into the output files, the macro AC_SUBST must be called with that variable name as an argument. Any occurrences of ‘@variable@’ for other variables are left unchanged. See Setting Output Variables, for more information on creating output variables with AC_SUBST.

A software package that uses a configure script should be distributed with a file Makefile.in, but no makefile; that way, the user has to properly configure the package for the local system before compiling it.

See Makefile Conventions in The GNU Coding Standards, for more information on what to put in makefiles.