How to read enviroment variables in dockerfile correctly

I have a Dockerfile where i am trying to read runtime args. Here is my dockerfile

FROM clojure:openjdk-8-lein-slim-buster
ENV dbconfig ""
ENTRYPOINT ["java","-Ddbconfig=${dbconfig}", "-jar", "abc.jar", "server"]
EXPOSE 8080

And here is the docker run command where i am passing values at runtime. Am i doing something wrong here? Values are always recognized as null. I have also tried removing ENV dbconfig "" but nothing works

docker run --rm -e dbconfig='{"somekey" "value"}' xyz/abc

You have two ways to define entrypoint : exec vs shell.

> The exec form is parsed as a JSON array, which means that you must use
> double-quotes (“) around words not single-quotes (‘).
So you use the exec form.

But :

> Unlike the shell form, the exec form does not invoke a command shell.
> This means that normal shell processing does not happen. For example,
> ENTRYPOINT [ "echo", "$HOME" ] will not do variable substitution on
> $HOME

So favor the shell form to allow env variable substitutions :

ENTRYPOINT java -Ddbconfig=${dbconfig} -jar abc.jar server

or invoke a shell in the exec form :

ENTRYPOINT [ "sh", "-c", "java","-Ddbconfig=${dbconfig}", "-jar", "abc.jar", "server" ]

Try using CMD to pass runtime arguments, sample like below

ENTRYPOINT ["/bin/bash"]
CMD ["/sample.sh", "argument1","argument2"]

Then passing arguments at runtime would be:-

docker run -i -t argument1 argument2