How do I use Docker environment variable in ENTRYPOINT array?

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"]

I SOLVED THIS VERY SIMPLY!

IMPORTANT: The variable which you wish to use in the ENTRYPOINT MUST be ENV type (and not ARG type).

EXAMPLE #1:

ARG APP_NAME=app.jar                    # $APP_NAME can be ARG or ENV type.
ENV APP_PATH=app-directory/$APP_NAME    # $APP_PATH must be ENV type.
ENTRYPOINT java -jar $APP_PATH

This will result with executing: java -jar app-directory/app.jar

EXAMPLE #2 (YOUR QUESTION):

ARG ADDRESSEE="world"                       # $ADDRESSEE can be ARG or ENV type.
ENV MESSAGE="Hello, $ADDRESSEE!"            # $MESSAGE must be ENV type.
ENTRYPOINT ./greeting --message $MESSAGE

This will result with executing: ./greeting --message Hello, world!

  • Please verify to be sure, whether you need quotation-marks "" when assigning string variables.

MY TIP: Use ENV instead of ARG whenever possible to avoid confusion on your part or the SHELL side.


After much pain, and great assistance from @vitr et al above, i decided to try

  • standard bash substitution
  • shell form of ENTRYPOINT (great tip from above)

and that worked. 

ENV LISTEN_PORT=""

ENTRYPOINT java -cp "app:app/lib/*" hello.Application --server.port=${LISTEN_PORT:-80}

e.g. 

docker run --rm -p 8080:8080 -d --env LISTEN_PORT=8080 my-image

and 

docker run --rm -p 8080:80 -d my-image

both set the port correctly in my container

Refs

see https://www.cyberciti.biz/tips/bash-shell-parameter-substitution-2.html


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\!"

Tags:

Docker

Dockerfile

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