Can make determine whether an environment variable is defined?

Question

AFAICT, ifdef in make works only for variables defined in the Makefile. Is there a way to check whether an environment variable is defined?

Answer 1

I don't know what you're doing (it's always best to include an actual example of what you have tried) but it definitely works:

$ cat Makefile
ifdef FOO
$(info FOO is defined)
endif
all:;@:

$ make

$ FOO=1 make
FOO is defined