Passing in env vars in 1.7.1

I am using version 1.7.1 and that does not seem to support --build_arg. How can I access an env var in the Dockerfile at build time. I tried simply using $ENV_VAR but it does not seem to be recognized.

shouldn’t be --build-arg and not --build_arg? plus in the dockerfile did you get the argument passed?

That was a typo in my post. I did use --build-arg. The error I get is:

flag provided but not defined: --build-arg

Here is my command line:

docker build -t test --build-arg DEVEL=True .

From my reading of the 1.7 docs that command line option did not exist in that version.