23 When Automake Isn’t Enough

Automake’s implicit copying semantics means that many problems can be worked around by simply adding some make targets and rules to Makefile.in. Automake will ignore these additions.

There are some caveats to doing this. Although you can overload a target already used by Automake, it is often inadvisable, particularly in the topmost directory of a package with subdirectories. However, various useful targets have a ‘-local’ version you can specify in your Makefile.in. Automake will supplement the standard target with these user-supplied targets.

The targets that support a local version are all, info, dvi, ps, pdf, check, install-data, install-exec, uninstall, installdirs, installcheck and the various clean targets (mostlyclean, clean, distclean, and maintainer-clean). Note that there are no uninstall-exec-local or uninstall-data-local targets; just use uninstall-local. It doesn’t make sense to uninstall just data or just executables.

For instance, here is one way to install a file in /etc:

install-data-local:
        $(INSTALL_DATA) $(srcdir)/afile $(DESTDIR)/etc/afile

Some targets also have a way to run another target, called a hook, after their work is done. The hook is named after the principal target, with ‘-hook’ appended. The targets allowing hooks are install-data, install-exec, uninstall, dist, and distcheck.

For instance, here is how to create a hard link to an installed program:

install-exec-hook:
        ln $(DESTDIR)$(bindir)/program$(EXEEXT) \
           $(DESTDIR)$(bindir)/proglink$(EXEEXT)

Although cheaper and more portable than symbolic links, hard links will not work everywhere (for instance OS/2 does not have ln). Ideally you should fall back to cp -p when ln does not work. An easy way, if symbolic links are acceptable to you, is to add AC_PROG_LN_S to configure.in (see Particular Program Checks in The Autoconf Manual) and use $(LN_S) in Makefile.am.

For instance, here is how you could install a versioned copy of a program using $(LN_S):

install-exec-hook:
        cd $(DESTDIR)$(bindir) && \
          mv -f prog$(EXEEXT) prog-$(VERSION)$(EXEEXT) && \
          $(LN_S) prog-$(VERSION)$(EXEEXT) prog$(EXEEXT)

Note that we rename the program so that a new version will erase the symbolic link, not the real binary. Also we cd into the destination directory in order to create relative links.