(autocf21.info.gz) Setting Output Variables

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 6.2 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.
  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@
 

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