[Makefile] Explain .PHONY

Create Makefile

clean:
         touch b.sh

clean1:
         touch a.sh

.PHONY: clean1

Create a file was called clean

Execute make will show

make: 'clean' is up to date.

Execute make clean1 will show

touch a.sh

Reference:

• Phony Targets
• .PHONY makefile中的伪目标