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(autoconf.info)Setting Output Variables

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Setting Output Variables
========================

   One way to record the results of tests is to set "output variables",
which are shell variables whose values are substituted into files that
`configure' outputs.  The two macros below create new output variables.
Note: Preset Output Variables, for a list of output variables that
are always available.

 - Macro: AC_SUBST (VARIABLE)
     Create an output variable from a shell variable.  Make `AC_OUTPUT'
     substitute the variable VARIABLE into output files (typically one
     or more `Makefile's).  This means that `AC_OUTPUT' will replace
     instances of `@VARIABLE@' in input files with the value that the
     shell variable VARIABLE has when `AC_OUTPUT' is called.  The value
     of VARIABLE should not contain literal newlines.

 - Macro: AC_SUBST_FILE (VARIABLE)
     Another way to create an output variable from a shell variable.
     Make `AC_OUTPUT' insert (without substitutions) the contents of
     the file named by shell variable VARIABLE into output files.  This
     means that `AC_OUTPUT' will replace instances of `@VARIABLE@' in
     output files (such as `Makefile.in') with the contents of the file
     that the shell variable VARIABLE names when `AC_OUTPUT' is called.
     Set the variable to `/dev/null' for cases that do not have a file
     to insert.

     This macro is useful for inserting `Makefile' fragments containing
     special dependencies or other `make' directives for particular host
     or target types into `Makefile's.  For example, `configure.in'
     could contain:

          AC_SUBST_FILE(host_frag)dnl
          host_frag=$srcdir/conf/sun4.mh

     and then a `Makefile.in' could contain:

          @host_frag@