Cause makefile to error if an environment variable is not set?

Question

I'd like my makefile to crash if an environment variable is not set. This is what I have so far:

ifneq ($(shell echo $${VIRTUAL_ENV:+True}),True)
$(error Looks like no virtualenv is active)
endif

and it works!

I'm wondering if there's a more elegant way to do this, perhaps with make directly instead of calling $(shell ...) .

Thanks for your help!

Answer 1

You can make use of the origin function...

ifeq ($(origin VIRTUAL_ENV),undefined)
$(error Looks like no virtualenv is active)
endif

Answer 2

This could be simplest option, but isn't as fine tuned as using origin .

ifndef VIRTUAL_ENV
$(error Looks like no virtualenv is active)
endif

One caveat here is that you can't distinguish if VIRTUAL_ENV defined in the Makefile or in the environment.

As @KurtisRader pointed out in a comment , this is possible because environment vars are implicitly "imported" into make's namespace https://www.gnu.org/software/make/manual/html_node/Environment.html .