make: Recipes/Search
4.5.4 Writing Recipes with Directory Search
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When a prerequisite is found in another directory through directory
search, this cannot change the recipe of the rule; they will execute as
written. Therefore, you must write the recipe with care so that it will
look for the prerequisite in the directory where 'make' finds it.
This is done with the "automatic variables" such as '$^' (
Automatic Variables). For instance, the value of '$^' is a list of
all the prerequisites of the rule, including the names of the
directories in which they were found, and the value of '$@' is the
target. Thus:
foo.o : foo.c
cc -c $(CFLAGS) $^ -o $@
(The variable 'CFLAGS' exists so you can specify flags for C compilation
by implicit rules; we use it here for consistency so it will affect all
C compilations uniformly; Variables Used by Implicit Rules
Implicit Variables.)
Often the prerequisites include header files as well, which you do
not want to mention in the recipe. The automatic variable '$<' is just
the first prerequisite:
VPATH = src:../headers
foo.o : foo.c defs.h hack.h
cc -c $(CFLAGS) $< -o $@
Info Catalog
make: Search Algorithm
make: Directory Search
make: Implicit/Search