[SOLVED] Running shell script in container when connecting with docker exec

Issue

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 $

Solution

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.

Answered By - Nick ODell

Answer Checked By - Gilberto Lyons (WPSolving Admin)