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

The downside of using docker exec is that it requires a running container, so docker inspect -f might be handy if you're unsure a container is running.

Example #1. Output a list of space-separated environment variables in the specified container:

docker inspect -f \
   '{{range $index, $value := .Config.Env}}{{$value}} {{end}}' container_name

the output will look like this:

ENV_VAR1=value1 ENV_VAR2=value2 ENV_VAR3=value3

Example #2. Output each env var on new line and grep the needed items, for example, the mysql container's settings could be retrieved like this:

docker inspect -f \
    '{{range $index, $value := .Config.Env}}{{println $value}}{{end}}' \
    container_name | grep MYSQL_

will output:

MYSQL_PASSWORD=secret
MYSQL_ROOT_PASSWORD=supersecret
MYSQL_USER=demo
MYSQL_DATABASE=demodb
MYSQL_MAJOR=5.5
MYSQL_VERSION=5.5.52

Example #3. Let's modify the example above to get a bash friendly output which can be directly used in your scripts:

docker inspect -f \
   '{{range $index, $value := .Config.Env}}export {{$value}}{{println}}{{end}}' \
   container_name | grep MYSQL

will output:

export MYSQL_PASSWORD=secret
export MYSQL_ROOT_PASSWORD=supersecret
export MYSQL_USER=demo
export MYSQL_DATABASE=demodb
export MYSQL_MAJOR=5.5
export MYSQL_VERSION=5.5.52

If you want to dive deeper, then go to Go’s text/template package documentation with all the details of the format.