Automake supports a simple type of conditionals.
Before using a conditional, you must define it by using
AM_CONDITIONAL
in the configure.ac file (see Macros).
The conditional name, conditional, should be a simple string starting with a letter and containing only letters, digits, and underscores. It must be different from TRUE and FALSE that are reserved by Automake.
The shell condition (suitable for use in a shell
if
statement) is evaluated when configure is run. Note that you must arrange for everyAM_CONDITIONAL
to be invoked every time configure is run. IfAM_CONDITIONAL
is run conditionally (e.g., in a shellif
statement), then the result will confuse automake.
Conditionals typically depend upon options that the user provides to the configure script. Here is an example of how to write a conditional that 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 Conditional Programs).
You may only test a single variable in an if
statement, possibly
negated using !. The else
statement may be omitted.
Conditionals may be nested to any depth. You may specify an argument to
else
in which case it must be the negation of the condition used
for the current if
. Similarly you may specify the condition
that is closed by an end
:
if DEBUG DBG = debug else !DEBUG DBG = endif !DEBUG
Unbalanced conditions are errors.
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.