I recently published a post on the Red Hat Developer Blog about the Atomic command that we’ve been working on for the last few months.

The Atomic command (/usr/bin/atomic) is a high-level, coherent entrypoint for Atomic Host systems, and aims to fill in the gaps in Linux container implementations.

One of the first questions I received was about environment substitution. The user wanted to have standard Bash substitutions working with /usr/bin/atomic. Specifically, he wanted to allow substitutions like $PWD/.foobar and --user=$(id -u).

I decided to try this out by creating a simple Dockerfile.

from rhel7
LABEL RUN echo $PWD/.foobar --user=$(id -u)

Then I build the container

docker build -t test .

Then, I’ll execute atomic run test

atomic run test

Looking at the label using docker inspect, I see that building the container dropped the $() content.

So, I’ll change the Dockerfile to quote it.

from rhel7
LABEL RUN echo '$PWD/.foobar' '--user=$(id -u)'

Build the container

docker build -t test .

Let’s run it again:

atomic run test
echo $PWD/.foobar --user=$(id -u)
/root/test1/.foobar --user=0


Woohoo, it works! If you want to take advantage of environment variables in your LABEL RUN statements, make sure to quote them so they’re passed through appropriately.

Have more questions about the atomic command? Leave a comment here, or ask on the atomic@projectatomic.io.