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Re: cascading variable resolution in AC_SUBST
From: |
Akim Demaille |
Subject: |
Re: cascading variable resolution in AC_SUBST |
Date: |
04 Oct 2001 17:55:21 +0200 |
User-agent: |
Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.4 (Artificial Intelligence) |
>>>>> "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.