We’ve dockerized all of the apps the comprise our platform at work. Almost all of the configuration data that our apps need is provided via environment variables. Sometimes I need to verify that the correct configuration was provided for a particular environment variable.
I’ve executed the following command enough times now that I figured I should write it down somewhere.
# $cid is the target container's ID, and $var is some part of the environment variable's name
docker inspect -f '{{range $_, $e := .Config.Environment}}{{println $e}}{{end}}' $cid | grep $var
This executes docker inspect with a Go template that will loop through the container’s environment variables (which are stored as a flat array of strings like ["VAR1=value1", "VAR2=value2"]) and print each variable on a new line. That output is piped to grep which searches for the environment variable I’m after.
To spice it up a bit: if there’s only one container running, then there’s no need to know its CID.
docker ps -q | xargs docker inspect -f '{{range $_, $e := .Config.Environment}}{{println $e}}{{end}}' | grep $var
docker ps -q will list just the CIDs of the running containers. Pipe this to xargs followed by the docker inspect command above, and the CID of the one running container will effectively be added as the last argument to the command.