How do I use Docker environment variable in ENTRYPOINT array

Question

If I set an environment variable  say ENV ADDRESSEE world  and I want to use it in the entry point script concatenated into a fixed string like   ENTRYPOINT     greeting    --message    Hello  world      with world being the value of the environment varible  how do I do it  I tried using  Hello   ADDRESSEE  but that doesn t seem to work  as it takes the  ADDRESSEE literally

User · Answer

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

User · Answer

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

User · Answer

I tried to resolve with the suggested answer and still ran into some issues    This was a solution to my problem  ARG APP EXE  quot AppName exe quot  ENV  EXE   APP EXE     Build a shell script because the ENTRYPOINT command doesn t like using ENV RUN echo  quot    bin bash  n mono    EXE  quot   gt    entrypoint sh RUN chmod  x   entrypoint sh    Run the generated shell script  ENTRYPOINT   quot   entrypoint sh quot    Specifically targeting your problem  RUN echo  quot    bin bash  n   greeting --message   ADDRESSEE  quot   gt    entrypoint sh RUN chmod  x   entrypoint sh ENTRYPOINT   quot   entrypoint sh quot

[docker] How do I use Docker environment variable in ENTRYPOINT array?

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