Docker Entrypoint environment variables not printed

Question

I'm new to Docker. All I want is to print an environment variable I pass to docker run via the -e flag. My Dockerfile looks like this:

FROM openjdk:8-jdk-alpine
ENTRYPOINT echo $TEST

I build my image with docker build -t test-docker . and execute it with docker run test-docker -e TEST=bar . It just prints an empty line and exits.

Answer 1

This happens because you run the image having parameters in wrong order, should be:

docker run --rm -e TEST=bar test-docker

Notice the env var is specified before the image name. Everything after your image name is considered as an argument of your container.

Use --rm always when playing to prevent garbage containers from piling up.