Re: cascading variable resolution in AC_SUBST

[Akim Demaille]

>>>>> "Raja" == Raja R Harinath <Raja> writes:

Raja> Hi, David Oleszkiewicz <address@hidden> writes:

>> so i want to do something like this
>> 
>> configure.in: PROGNAME = "foo" DIR = "${bindir}/${PROG}"
>> AC_SUBST(DIR)
>> 
>> myfile.h.in: #define DIR "@DIR@"
>> 
>> when things resolve out to myfile.h i get #define CONF_DIR
>> "${exec_prefix}/foo"

Raja> Look at the GNU Autoconf Macro Archive for 'AC_DEFINE_DIR'.

Or read the documentation.

   Most of these variables have values that rely on `prefix' or
`exec_prefix'.  It is on purpose that the directory output variables
keep them unexpanded: typically address@hidden@' will be replaced by
`${prefix}/share', not `/usr/local/share'.

   This behavior is mandated by the GNU coding standards, so that when
the user runs:

`make'
     she can still specify a different prefix from the one specified to
     `configure', in which case, if needed, the package shall hard code
     dependencies to her late desires.

`make install'
     she can specify a different installation location, in which case
     the package _must_ still depend on the location which was compiled
     in (i.e., never recompile when `make install' is run).  This is an
     extremely important feature, as many people may decide to install
     all the files of a package grouped together, and then install
     links from the final locations to there.

   In order to support these features, it is essential that `datadir'
remains being defined as `${prefix}/share' to depend upon the current
value of `prefix'.

   A corollary is that you should not use these variables but in
Makefiles.  For instance, instead of trying to evaluate `datadir' in
`configure' and hardcoding it in Makefiles using e.g.
`AC_DEFINE_UNQUOTED(DATADIR, "$datadir")', you should add
`-DDATADIR="$(datadir)"' to your `CPPFLAGS'.

   Similarly you should not rely on `AC_OUTPUT_FILES' to replace
`datadir' and friends in your shell scripts and other files, rather let
`make' manage their replacement.  For instance Autoconf ships templates
of its shell scripts ending with `.sh', and uses this Makefile snippet:

     .sh:
             rm -f $@ address@hidden
             sed 's,@datadir\@,$(pkgdatadir),g' $< >address@hidden
             chmod +x address@hidden
             mv address@hidden $@

   Three things are noteworthy:

address@hidden@'
     The backslash prevents `configure' from replacing address@hidden@' in
     the sed expression itself.

`$(pkgdatadir)'
     Don't use address@hidden@'!  Use the matching makefile variable
     instead.

`,'
     Don't use `/' in the sed expression(s) since most probably the
     variables you use, such as `$(pkgdatadir)', will contain some.