%% Vilar Camara Neto <[EMAIL PROTECTED]> writes:
vcn> I'm trying to build a rule with an "optional" prerequisite, i.e.,
vcn> something that says that "if a given file doesn't exist, then
vcn> ignore it, otherwise consider it as a prerequisite".
You can't really do this with pattern rules.
vcn> Surprisingly, a patterned rule doesn't work as I expect:
vcn> %.z: %.x $(wildcard %.y)
Not a surprise to me :-). All functions and variables in a target or
prerequisite list are expanded immediately, as the makefile is parsed.
However, evaluation of patterns like %.y doesn't happen until much
later, when make is trying to find rules to build targets.
The above does a wildcard on the literal string '%.y', which, unless you
have a file by that name in your directory, expands to the empty string.
vcn> How do I solve it? Maybe not using "$(wildcard ...)" at all?
All you can do is something like this:
%.z: %.x
...
all: foo.z bar.z
foo.z: $(wildcard foo.y)
bar.z: $(wildcard bar.y)
You can do the latter using a loop and avoid writing it out. if you have
a GNU make sufficiently new to have the $(eval ...) function.
--
-------------------------------------------------------------------------------
Paul D. Smith <[EMAIL PROTECTED]> Find some GNU make tips at:
http://www.gnu.org http://make.paulandlesley.org
"Please remain calm...I may be mad, but I am a professional." --Mad Scientist
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