6.12 Pattern-specific Variable Values

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 specified.

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.

For example:

%.o : CFLAGS = -O

will assign CFLAGS the value of ‘-O’ for all targets matching the pattern %.o.

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 CFLAGS variable 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.