CODEWITHSUNDEEP
makefilegnu-make
Dummy00001
Dummy00001

Reputation: 17450

Make pattern rule for subdirectories

While testing the parallelization possibilities in case of recursive make, I have stumbled on a weird behavior with the pattern rules.

The Makefile:

## prepare the dir structure
# mkdir -p bs{1,2,3}
# for i in 1 2 3; do ln -s ../Makefile bs$i ; done

aaa:
        @echo $(CURDIR)
        sleep 1

s: bs1 bs2 bs3
        true

## alt1
bs1 bs2 bs3: ; +make -C $@ aaa

## alt2
#bs%: ; +make -C $@ aaa

.PHONY: s bs1 bs2 bs3

There are two alternatives how to specify the targets: either literally list all the targets in the recipe, alt1 - bs1 bs2 bs3 - or use the % pattern, alt2 - bs%.

When I run make -j s with the alt1, it works as expected.

But if I switch to alt2 (comment out alt1 rule, comment in alt2 rule), the make -j s runs only the true, and silently ignores the prerequisite bs1, bs2 and bs3 targets.

Likewise, with alt1, make bs1 calls the sub-make, while with alt2, make bs1 says that Nothing to be done for 'bs1'. The trick with the .force dummy target didn't change the behavior.

Why?

Upvotes: 1

Views: 605

Answers (1)

user657267
user657267

Reputation: 21040

From the manual

The implicit rule search (see Implicit Rules) is skipped for .PHONY targets.

bs%: is an implicit rule, so it is ignored.

Upvotes: 1

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