# Makefile Phony Targets

**Phony targets** don't produce files—they're commands. Mark them with `.PHONY` so Make doesn't check for a file with that name.

```makefile
.PHONY: all clean install test

all: app

app: main.o util.o
	gcc -o app main.o util.o

clean:
	rm -f *.o app

install: app
	cp app /usr/local/bin/

test: app
	./test.sh
```

Without `.PHONY`, if a file named `clean` exists, `make clean` won't run (Make thinks the target is up to date). `.PHONY` tells Make "this target is not a file; run it every time."

**Common phony targets:**

```makefile
.PHONY: all clean install test help

all:
	@echo "Building application"
	gcc -o app *.c

clean:
	rm -f *.o app

install: all
	mkdir -p /usr/local/bin
	cp app /usr/local/bin/

test: all
	./run_tests.sh

help:
	@echo "Usage: make [target]"
	@echo "Targets:"
	@echo "  all     - build application (default)"
	@echo "  clean   - delete build artifacts"
	@echo "  install - install to /usr/local/bin"
	@echo "  test    - run tests"
```

**`all` target:** Conventionally, `all` is the default target. If no target is specified, `make all` runs:

```makefile
.PHONY: all
all: app

app: main.o util.o
	gcc -o app main.o util.o
```

`make` with no arguments is equivalent to `make all`.

**`clean` target:** Delete build artifacts:

```makefile
.PHONY: clean
clean:
	rm -f *.o *.so app
	rm -rf build/
```

Run with `make clean` before rebuilding to start fresh.

**`install` target:** Copy built files to their destination:

```makefile
.PHONY: install
install: all
	install -d $(PREFIX)/bin
	install -m 755 app $(PREFIX)/bin/app
```

Depends on `all` (builds first), then installs. `$(PREFIX)` allows customization (`make PREFIX=/opt install`).

**`test` target:** Run tests:

```makefile
.PHONY: test
test: app
	./test_app
	@echo "Tests passed"
```

Depends on `app` (ensures app is built), then runs the test.

**`help` target:** Document available targets:

```makefile
.PHONY: help
help:
	@echo "Available targets:"
	@grep "^.PHONY:" Makefile | sed 's/.PHONY: //' | tr ' ' '\n' | grep -v "^$$"
```

The `@` prefix suppresses command echoing; only the output is printed. Good for documentation.

**Avoiding accidental files:** If you have both a phony target and a file with the same name, the phony target always runs:

```makefile
.PHONY: build
build:
	mkdir -p build
```

Without `.PHONY`, if `build/` directory exists, `make build` would do nothing.