.PHONY Targets

Scope: targets that are tasks, not files — and the silent failure when you forget .PHONY.

Tasks vs files

So far every target has been a file. But clean doesn't build anything — it does something:

clean:
    rm -f hello *.o

Targets like clean, test, install, backup are phony: they name a task, not a file. Tell Make with the special .PHONY target:

.PHONY: clean
clean:
    rm -f hello *.o

The trap

Without .PHONY, Make treats clean like a file. If no file named clean exists, the recipe runs — fine. But the day a file named clean appears (a stray download, a typo'd redirect), Make sees an up-to-date "target" and silently skips the recipe:

$ touch clean
$ make clean
make: 'clean' is up to date.

Your cleanup didn't run, Make reported success (exit 0), and nothing looks wrong. This actually happened while testing this guide. With .PHONY: clean, the recipe always runs:

$ make clean
rm -f hello *.o

Rule of thumb: if a target doesn't produce a file with its own name, declare it .PHONY. List them all in one place near the top of the file:

.PHONY: all clean test install backup

all is the conventional first target — the thing plain make builds — and it's phony too, since it produces no file itself:

.PHONY: all clean
all: hello

What .PHONY does not do

It doesn't change dependency order, and it doesn't make prerequisites run "more." A phony target's prerequisites still build normally; only the phony target itself is always considered out of date.

Check: make -p | grep -B1 'Phony target' lists the phony targets Make knows about. If your task target isn't there, you forgot the declaration:

$ make -p | grep -B1 'Phony target'
clean:
#  Phony target (prerequisite of .PHONY).
--
all: hello
#  Phony target (prerequisite of .PHONY).