18 Conditionals

Automake supports a simple type of conditionals.

Before using a conditional, you must define it by using AM_CONDITIONAL in the configure.in file (see Autoconf macros supplied with Automake). The AM_CONDITIONAL macro takes two arguments.

The first argument to AM_CONDITIONAL is the name of the conditional. This should be a simple string starting with a letter and containing only letters, digits, and underscores.

The second argument to AM_CONDITIONAL is a shell condition, suitable for use in a shell if statement. The condition is evaluated when configure is run.

Conditionals typically depend upon options which the user provides to the configure script. Here is an example of how to write a conditional which is true if the user uses the ‘--enable-debug’ option.

AC_ARG_ENABLE(debug,
[  --enable-debug    Turn on debugging],
[case "${enableval}" in
  yes) debug=true ;;
  no)  debug=false ;;
  *) AC_MSG_ERROR(bad value ${enableval} for --enable-debug) ;;
esac],[debug=false])
AM_CONDITIONAL(DEBUG, test x$debug = xtrue)

Here is an example of how to use that conditional in Makefile.am:

if DEBUG
DBG = debug
else
DBG =
endif
noinst_PROGRAMS = $(DBG)

This trivial example could also be handled using EXTRA_PROGRAMS (see Building a program).

You may only test a single variable in an if statement. The else statement may be omitted. Conditionals may be nested to any depth.

Note that conditionals in Automake are not the same as conditionals in GNU Make. Automake conditionals are checked at configure time by the configure script, and affect the translation from Makefile.in to Makefile. They are based on options passed to configure and on results that configure has discovered about the host system. GNU Make conditionals are checked at make time, and are based on variables passed to the make program or defined in the Makefile.

Automake conditionals will work with any make program.