13. What Gets Cleaned

The GNU Makefile Standards specify a number of different clean rules. See (standards)Standard Targets section `Standard Targets for Users' in The GNU Coding Standards.

Generally the files that can be cleaned are determined automatically by Automake. Of course, Automake also recognizes some variables that can be defined to specify additional files to clean. These variables are MOSTLYCLEANFILES, CLEANFILES, DISTCLEANFILES, and MAINTAINERCLEANFILES.

When cleaning involves more than deleting some hard-coded list of files, it is also possible to supplement the cleaning rules with your own commands. Simply define a rule for any of the mostlyclean-local, clean-local, distclean-local, or maintainer-clean-local targets (see section Extending Automake Rules). A common case is deleting a directory, for instance, a directory created by the test suite:

clean-local:
        -rm -rf testSubDir

Since make allows only one set of rules for a given target, a more extensible way of writing this is to use a separate target listed as a dependency:

clean-local: clean-local-check
.PHONY: clean-local-check
clean-local-check:
        -rm -rf testSubDir

As the GNU Standards aren't always explicit as to which files should be removed by which rule, we've adopted a heuristic that we believe was first formulated by François Pinard:

• If make built it, and it is commonly something that one would want to rebuild (for instance, a ‘.o’ file), then mostlyclean should delete it.
• Otherwise, if make built it, then clean should delete it.
• If configure built it, then distclean should delete it.
• If the maintainer built it (for instance, a ‘.info’ file), then maintainer-clean should delete it. However maintainer-clean should not delete anything that needs to exist in order to run ‘./configure && make’.

We recommend that you follow this same set of heuristics in your ‘Makefile.am’.