8.1.4 Conditional compilation of programs

Sometimes it is useful to determine the programs that are to be built at configure time. For instance, GNU cpio only builds mt and rmt under special circumstances. The means to achieve conditional compilation of programs are the same you can use to compile source files conditionally: substitutions or conditionals.

Conditional Programs using configure Substitutions

In this case, you must notify Automake of all the programs that can possibly be built, but at the same time cause the generated ‘Makefile.in’ to use the programs specified by configure. This is done by having configure substitute values into each _PROGRAMS definition, while listing all optionally built programs in EXTRA_PROGRAMS.

bin_PROGRAMS = cpio pax $(MT)
libexec_PROGRAMS = $(RMT)
EXTRA_PROGRAMS = mt rmt

As explained in Support for executable extensions, Automake will rewrite bin_PROGRAMS, libexec_PROGRAMS, and EXTRA_PROGRAMS, appending ‘$(EXEEXT)’ to each binary. Obviously it cannot rewrite values obtained at run-time through configure substitutions, therefore you should take care of appending ‘$(EXEEXT)’ yourself, as in ‘AC_SUBST([MT], ['mt${EXEEXT}'])’.

Conditional Programs using Automake Conditionals

You can also use Automake conditionals (see section Conditionals) to select programs to be built. In this case you don't have to worry about ‘$(EXEEXT)’ or EXTRA_PROGRAMS.

bin_PROGRAMS = cpio pax
if WANT_MT
  bin_PROGRAMS += mt
endif
if WANT_RMT
  libexec_PROGRAMS = rmt
endif