5.1.1.2 EXTRA_ Automake variables

For each primary, there is one additional variable named by prefixing ‘EXTRA_’ to the primary name. This variable contains a list of the objects that may or may not be built, depending on what configure decides. The author of Makefile.am must use this variable if there are objects like these, so that Automake can generate a Makefile.in that will work in all cases.

For instance, cpio decides at configure time which programs should be built. Some of the programs are installed in bindir, and some are installed in sbindir:

EXTRA_PROGRAMS = mt rmt
bin_PROGRAMS = cpio pax
sbin_PROGRAMS = $(MORE_PROGRAMS)

Defining a primary without a prefix as a variable, e.g., ‘PROGRAMS’, is an error.