1 TEST_VAR := haha
 2 ifneq ($(strip $(TEST_VAR)),)
 3         $(info print var $(TEST_VAR))
 4 endif
 5
 6 all: hello
 7         gcc hello.c
 8
 9 .PHONY:mclean
10 mclean:
11         $(info PHONY target is mclean)
12         rm hello a.out