How do I use Docker environment variable in ENTRYPOINT array?

Solution 1:

You're using the exec form of ENTRYPOINT. 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. If you want shell processing then either use the shell form or execute a shell directly, for example: ENTRYPOINT [ "sh", "-c", "echo $HOME" ].
When using the exec form and executing a shell directly, as in the case for the shell form, it is the shell that is doing the environment variable expansion, not docker.(from Dockerfile reference)

In your case, I would use shell form

ENTRYPOINT ./greeting --message "Hello, $ADDRESSEE\!"

Solution 2:

I tried to resolve with the suggested answer and still ran into some issues...

This was a solution to my problem:

ARG APP_EXE="AppName.exe"
ENV _EXE=${APP_EXE}

# Build a shell script because the ENTRYPOINT command doesn't like using ENV
RUN echo "#!/bin/bash \n mono ${_EXE}" > ./entrypoint.sh
RUN chmod +x ./entrypoint.sh

# Run the generated shell script.
ENTRYPOINT ["./entrypoint.sh"]

Specifically targeting your problem:

RUN echo "#!/bin/bash \n ./greeting --message ${ADDRESSEE}" > ./entrypoint.sh
RUN chmod +x ./entrypoint.sh
ENTRYPOINT ["./entrypoint.sh"]