Question 81437 in Docker Question posted in
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Running shell script in container when connecting with docker exec

I would like to run a shell script every time when a shell is started using docker exec or kubectl exec. I am looking for something similar to .bashrc/.bash_profile/.profile, but since this particular container is based on alpine linux, bash is not available.

How could I execute a shell script in the container?

I would like to achieve something like this:

> docker exec -it my_alpine_based_container sh
Hi! Welcome to the container. This message comes from a shell script.
/usr/src/app $

And similarly with kubectl:

> kubectl exec -it my_pod_running_the_container -- sh
Hi! Welcome to the container. This message comes from a shell script.
/usr/src/app $
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2

Answers


  1. Chosen as BEST ANSWER
    0

    When using the busybox ash variant, which is used by Alpine Linux as well, it is possible to set the ENV variable in the Dockerfile to point to a script that is executed on startup - even for not login shells.

    For details see the busybox ash source code: ash.c, line 14189.

    Dockerfile:

    FROM alpine:latest
ENV ENV=/root/.ashrc
RUN echo "echo 'Hello from .ashrc!'" >> /root/.ashrc
CMD ["/bin/sh"]

    Test:

     $ docker exec -it c8688d3e9ce8 sh
Hello from .ashrc!
/ #

  2. 0

    Alpine linux uses ash for /bin/sh. Ash does support .profile, but only when running as a login shell.

    Here is an example Dockerfile which prints a welcome message:

    FROM alpine:latest
RUN echo 'echo foo' >> /root/.profile
CMD ["/bin/sh", "-l"]

    Here’s it in action:

    $ docker run -it <image name>
foo
ccdae0bb9d59:/#

    Now, this doesn’t fit one of your requirements, because if you run:

    docker exec -it <container name> sh

    the message will not print, because it’s missing the -l option.

    but since this particular container is based on alpine linux, bash is not available.

    Bash is a pretty lightweight addition to the image. If you add Bash to your image like this, then it only adds 4.6 MB to the image.

    RUN apk add bash

    I would say that’s worth it if it makes your service easier to debug.

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