make: Force Targets
1
1 4.7 Rules without Recipes or Prerequisites
1 ==========================================
1
1 If a rule has no prerequisites or recipe, and the target of the rule is
1 a nonexistent file, then 'make' imagines this target to have been
1 updated whenever its rule is run. This implies that all targets
1 depending on this one will always have their recipe run.
1
1 An example will illustrate this:
1
1 clean: FORCE
1 rm $(objects)
1 FORCE:
1
1 Here the target 'FORCE' satisfies the special conditions, so the
1 target 'clean' that depends on it is forced to run its recipe. There is
1 nothing special about the name 'FORCE', but that is one name commonly
1 used this way.
1
1 As you can see, using 'FORCE' this way has the same results as using
1 '.PHONY: clean'.
1
1 Using '.PHONY' is more explicit and more efficient. However, other
1 versions of 'make' do not support '.PHONY'; thus 'FORCE' appears in many
1 makefiles. ⇒Phony Targets.
1