(make.info)Force Targets

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Rules without Commands or Dependencies

   If a rule has no dependencies 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)

   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.  Note: Phony Targets.

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