Get Environment Variable from Docker Container

Question

What\'s the simplest way to get an environment variable from a docker container that has not been declared in the Dockerfile?

For instance, an environment v

Answer 1

To view all env variables:

docker exec container env

To get one:

docker exec container env | grep VARIABLE | cut -d'=' -f2

Answer 2

@aisbaa's answer works if you don't care when the environment variable was declared. If you want the environment variable, even if it has been declared inside of an exec /bin/bash session, use something like:

IFS="=" read -a out <<< $(docker exec container /bin/bash -c "env | grep ENV_VAR" 2>&1)

It's not very pretty, but it gets the job done.

To then get the value, use:

echo ${out[1]}

Answer 3

None of the above answers show you how to extract a variable from a non-running container (if you use the echo approach with run, you won't get any output).

Simply run with printenv, like so:

docker run --rm <container> printenv <MY_VAR>

(Note that docker-compose instead of docker works too)

Answer 4

This command inspects docker stack processes' environment in the host :

pidof   dockerd containerd containerd-shim | tr ' ' '\n' \
      | xargs -L1 -I{} -- sudo xargs -a '/proc/{}/environ' -L1 -0

Answer 5

If by any chance you use VSCode and has installed the docker extension, just right+click on the docker you want to check (within the docker extension), click on Inspect, and there search for env, you will find all your env variables values

Answer 6

The proper way to run echo "$ENV_VAR" inside the container so that the variable substitution happens in the container is:

docker exec <container_id> bash -c 'echo "$ENV_VAR"'