In addition to target-specific variable values
(see Target-specific Variable Values), GNU
make supports pattern-specific variable values. In this form,
the variable is defined for any target that matches the pattern
Set a pattern-specific variable value like this:
pattern … : variable-assignment
where pattern is a %-pattern. As with target-specific variable
values, multiple pattern values create a pattern-specific variable
value for each pattern individually. The variable-assignment can
be any valid form of assignment. Any command line variable setting will
take precedence, unless
override is specified.
%.o : CFLAGS = -O
CFLAGS the value of ‘-O’ for all targets
matching the pattern
If a target matches more than one pattern, the matching pattern-specific variables with longer stems are interpreted first. This results in more specific variables taking precedence over the more generic ones, for example:
%.o: %.c $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@ lib/%.o: CFLAGS := -fPIC -g %.o: CFLAGS := -g all: foo.o lib/bar.o
In this example the first definition of the
will be used to update lib/bar.o even though the second one
also applies to this target. Pattern-specific variables which result
in the same stem length are considered in the order in which they
were defined in the makefile.
Pattern-specific variables are searched after any target-specific variables defined explicitly for that target, and before target-specific variables defined for the parent target.