Makefile variables from command line vs. environment

Question

Is there a way to detect whether a variable has been set from the environment vs. on the command line?

I would like to distinguish between someone invoking make with make LIB=mylib vs. make and $LIB being defined.

Answer 1

Yes. You can use the origin function to determine where a variable was defined.

ifneq (,$(findstring environment,$(origin LIB)))
    # LIB was defined by the environment
else
    # LIB was defined some other way
endif