It says this:
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 recipe. 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’.
This may be at least mostly true for the particular case of the clean
target, which is generally invoked explicitly. However, its not true
for the common case of an object file that one wants to always
rebuild.
This Makefile:
%.o: %.c
cp $< $@ # Simulate compile
#.PHONY: test.o
test.o: FORCE
FORCE:
test.o: Makefile
fooprog: test.o
cp $< $@ # Simulate link
Will always recompile test.c into test.o as it is, but if the test.o:
FORCE and FORCE: rules are replaced with the .PHONY: test.o rule
(commented out above), then test.o will never be built at all.
I think the description in 4.7 goes too far in implying equivalency.
Either it shouldn't say the two are equivalent, or it should be more
careful to qualify that that they are equivalent only in the
particular case of the explicitly invoked phony target which doesn't
have additional dependencies expressed in other rules.
Britton
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