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4.8.2 Installation Directory Variables
--------------------------------------

The following variables specify the directories for package
installation, see *note Variables for Installation Directories:
(standards)Directory Variables, for more information. Each variable
corresponds to an argument of ‘configure’; trailing slashes are stripped
so that expressions such as ‘${prefix}/lib’ expand with only one slash
between directory names. 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 idiosyncratic read-only
architecture-independent data.

-- Variable: datarootdir
The root of the directory tree for read-only
architecture-independent data files.

-- Variable: docdir
The directory for installing documentation files (other than Info
and man).

-- Variable: dvidir
The directory for installing documentation files in DVI format.

-- 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: htmldir
The directory for installing HTML documentation.

-- 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: localedir
The directory for installing locale-dependent but
architecture-independent data, such as message catalogs. This
directory usually has a subdirectory per locale.

-- Variable: localstatedir
The directory for installing modifiable single-machine data.
Content in this directory typically survives a reboot.

-- Variable: runstatedir
The directory for installing temporary modifiable single-machine
data. Content in this directory survives as long as the process is
running (such as pid files), as contrasted with ‘/tmp’ that may be
periodically cleaned. Conversely, this directory is typically
cleaned on a reboot. By default, this is a subdirectory of
‘localstatedir’.

-- 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: pdfdir
The directory for installing PDF documentation.

-- 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: psdir
The directory for installing PostScript documentation.

-- 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 ‘@datarootdir@’ is replaced by
‘${prefix}/share’, not ‘/usr/local/share’, and ‘@datadir@’ is replaced
by ‘${datarootdir}’.

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 should 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
‘datarootdir’ remains defined as ‘${prefix}/share’, so that its value
can be expanded based on 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], ["$datadir"], [Data directory.])’, you
should add ‘-DDATADIR='$(datadir)'’ to your makefile's definition of
‘CPPFLAGS’ (‘AM_CPPFLAGS’ if you are also using Automake).

Similarly, you should not rely on ‘AC_CONFIG_FILES’ to replace
‘bindir’ and friends in your shell scripts and other files; instead, let
‘make’ manage their replacement. For instance Autoconf ships templates
of its shell scripts ending with ‘.in’, and uses a makefile snippet
similar to the following to build scripts like ‘autoheader’ and
‘autom4te’:

autoheader autom4te: Makefile
rm -f $@ $@.tmp
srcdir=''; \
test -f ./$@.in || srcdir=$(srcdir)/; \
$(edit) $${srcdir}$@.in >$@.tmp
chmod +x $@.tmp
chmod a-w $@.tmp
mv $@.tmp $@

autoheader: $(srcdir)/autoheader.in
autom4te: $(srcdir)/autom4te.in

Some details are noteworthy:

‘@bindir[@]’
The brackets prevent ‘configure’ from replacing ‘@bindir@’ in the
Sed expression itself. Brackets are preferable to a backslash
here, since Posix says ‘\@’ is not portable.

‘$(bindir)’
Don't use ‘@bindir@’! Use the matching makefile variable instead.

‘$(pkgdatadir)’
The example takes advantage of the variable ‘$(pkgdatadir)’
provided by Automake; it is equivalent to ‘$(datadir)/$(PACKAGE)’.

‘/’
Don't use ‘/’ in the Sed expressions that replace file names since
most likely the variables you use, such as ‘$(bindir)’, contain
‘/’. Use a shell metacharacter instead, such as ‘|’.

special characters
File names, file name components, and the value of ‘VPATH’ should
not contain shell metacharacters or white space. *Note Special
Chars in Variables::.

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’.

‘$@’
The main rule is generic, and uses ‘$@’ extensively to avoid the
need for multiple copies of the rule.

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 $@

*Note Single Suffix Rules::, for details.

‘$(srcdir)’
Be sure to specify the name of the source directory, otherwise the
package won't support separated builds.

For the more specific installation of Erlang libraries, the following
variables are defined:

-- Variable: ERLANG_INSTALL_LIB_DIR
The common parent directory of Erlang library installation
directories. This variable is set by calling the
‘AC_ERLANG_SUBST_INSTALL_LIB_DIR’ macro in ‘configure.ac’.

-- Variable: ERLANG_INSTALL_LIB_DIR_LIBRARY
The installation directory for Erlang library LIBRARY. This
variable is set by using the ‘AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR’
macro in ‘configure.ac’.

*Note Erlang Libraries::, for details.