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4.7.2 Installation Directory Variables

The following variables specify the directories where the package will be installed, see section `Variables for Installation Directories' in The GNU Coding Standards, for more information. See the end of this section for details on when and how to use these variables.

Variable: bindir
The directory for installing executables that users run.

Variable: datadir
The directory for installing read-only architecture-independent data.

Variable: exec_prefix
The installation prefix for architecture-dependent files. By default it's the same as prefix. You should avoid installing anything directly to exec_prefix. However, the default value for directories containing architecture-dependent files should be relative to exec_prefix.

Variable: includedir
The directory for installing C header files.

Variable: infodir
The directory for installing documentation in Info format.

Variable: libdir
The directory for installing object code libraries.

Variable: libexecdir
The directory for installing executables that other programs run.

Variable: localstatedir
The directory for installing modifiable single-machine data.

Variable: mandir
The top-level directory for installing documentation in man format.

Variable: oldincludedir
The directory for installing C header files for non-GCC compilers.

Variable: prefix
The common installation prefix for all files. If exec_prefix is defined to a different value, prefix is used only for architecture-independent files.

Variable: sbindir
The directory for installing executables that system administrators run.

Variable: sharedstatedir
The directory for installing modifiable architecture-independent data.

Variable: sysconfdir
The directory for installing read-only single-machine data.

Most of these variables have values that rely on prefix or exec_prefix. It is deliberate that the directory output variables keep them unexpanded: typically `@datadir@' 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 corresponding to the make-specified prefix.

`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 except in Makefiles. For instance, instead of trying to evaluate datadir in `configure' and hard-coding 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 `.in', and uses a Makefile snippet similar to:

 
edit = sed \
        -e 's,@datadir\@,$(pkgdatadir),g' \
        -e 's,@prefix\@,$(prefix),g'

autoconf: Makefile $(srcdir)/autoconf.in
        rm -f autoconf autoconf.tmp
        $(edit) $(srcdir)/autoconf.in >autoconf.tmp
        chmod +x autoconf.tmp
        mv autoconf.tmp autoconf

autoheader: Makefile $(srcdir)/autoheader.in
        rm -f autoheader autoheader.tmp
        $(edit) $(srcdir)/autoconf.in >autoheader.tmp
        chmod +x autoheader.tmp
        mv autoheader.tmp autoheader

Some details are noteworthy:

`@datadir\@'
The backslash prevents configure from replacing `@datadir@' in the sed expression itself.

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

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

`Dependency on `Makefile''
Since edit uses values that depend on the configuration specific values (prefix etc.) and not only on VERSION and so forth, the output depends on `Makefile', not `configure.ac'.

`Separated dependencies and Single Suffix Rules'
You can't use them! The above snippet cannot be (portably) rewritten as:

 
autoconf autoheader: Makefile
.in:
        rm -f $@ $@.tmp
        $(edit) $< >$@.tmp
        chmod +x $@.tmp
        mv $@.tmp $@

See section 10.10 Limitations of Make, for details.

``$(srcdir)''
Be sure to specify the path to the sources, otherwise the package won't support separated builds.


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