Rules without Commands or Prerequisites

If a rule has no prerequisites or commands, and the target of the rule is a nonexistent file, then make imagines this target to have been updated whenever its rule is run. This implies that all targets depending on this one will always have their commands run.

An example will illustrate this:

     clean: FORCE
             rm $(objects)
     FORCE:
     

Here the target FORCE satisfies the special conditions, so the target clean that depends on it is forced to run its commands. There is nothing special about the name FORCE, but that is one name commonly used this way.

As you can see, using FORCE this way has the same results as using .PHONY: clean.

Using .PHONY is more explicit and more efficient. However, other versions of make do not support .PHONY; thus FORCE appears in many makefiles. See Phony Targets.