How can I use environment variables in a docker run command?

Question

If I pass an environment variable which is set inside of the container as an argument to docker run, my shell evaluates it. For example:

I want my container to print the value of $FOO which is bar. None of these will work:

# Prints blank line
$ docker run -e FOO=bar ubuntu echo $FOO

# Prints '$FOO'
$ docker run -r FOO=bar ubuntu echo \$FOO

z0r · Accepted Answer · 2015-09-05 03:02:19Z

12

It works if you run echo in a shell:

$ sudo docker run --rm -e FOO=bar ubuntu bash -c 'echo $FOO'
bar

This is because echo is a command (/bin/echo), but it's the shell that does the variable substitution.

answered Sep 5, 2015 at 3:02

z0r

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2 Comments

Adrian Mouat Over a year ago

I don't think that's the reason; it's actually the host expanding the variable before it's sent to docker i.e. FOO="bar" && docker run ubuntu echo $FOO prints bar

z0r Over a year ago

The second part of the question escapes the variable as \$FOO, which prevents expansion and results in $FOO being printed.

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