How use ENV variables in Dockerfile ENTRYPOINT command

Question

I'm brand new user of Docker...

I'm tring use Enviroments variables on my Dockerfile...

It's like that:

FROM openjdk:11-jdk-slim-buster
ENV JAVA_APP my-app
EXPOSE 8080
COPY target/$JAVA_APP-*.jar /app/$JAVA_APP.jar
CMD java -jar /app/$JAVA_APP.jar

The result is that: the COPY command gets the value of JAVA_APP variable. But the CMD command doesn't.

Is there some another way to use ENV variables?

Answer 1

If I make this super simple Dockerfile

FROM ubuntu
ENV JAVA_APP my-app
CMD echo $JAVA_APP

and build and run it with

docker build -t test .
docker run --rm test
docker run --rm -e JAVA_APP=Hello test

It prints 'my-app' and 'Hello'. So it does work. If it still doesn't work for you, can you expand your post with the command you use to run the container?