Moby: How to make builder RUN use /bin/bash instead of /bin/sh

[dwatrous]

I'm creating a Dockerfile build script and would like to use bash commands. RUN uses /bin/sh by default. Is there some way to tell RUN to use /bin/bash instead?

[cpuguy83]

No, this hardcoded to "/bin/sh -c"
One could of course link /bin/bash to /bin/sh in a previous build step.

[dwatrous]

I ended up changing my Dockerfile script to copy a file and use that rather than use the redirection I had been using in bash.

[tiborvass]

@dwatrous did you try RUN ["echo", "hello"] will not be wrapped by /bin/sh IIRC. So if you absolutely want bash, you can invoke it: RUN ["/bin/bash", "-c", "echo hello all in one string"].
Let us know if it solves your problem.

[unclejack]

bash can be used manually by using it in RUN instructions.

There's no intention or plan to make it possible to change it to bash.

I'll mark this as a doc issue because we might want to document this. It's the third or fourth time this question has popped up.

[duglin]

PR: https://github.com/docker/docker/pull/7489

[duglin]

This can be closed now due to: https://github.com/docker/docker/pull/7489

[ORESoftware]

so what's the story on this one?

[thaJeztah]

@ORESoftware See the discussion above, and https://github.com/moby/moby/pull/22489, which added the SHELL Dockerfile instruction (Docker 1.12 and up)

• If you want to use a different shell for a single RUN, use the Exec form (JSON) notation - as is being discussed above:

  RUN ["/bin/bash", "-c", "echo I am now using bash!"]
  

• If you want to change the default shell in your image (and during build), use the SHELL Dockerfile instruction that was implemented in https://github.com/moby/moby/pull/22489:

  SHELL ["/bin/bash", "-c"]
  RUN echo I am now using bash!
  

• Or, a combination of the above

  FROM ubuntu
  RUN echo I am using the default (/bin/sh)
  RUN ["/bin/bash", "-c", "echo I am using bash"]
  SHELL ["/bin/bash", "-c"]
  RUN echo I am using bash, which is now the default
  RUN ["/bin/sh", "-c", "echo I am using /bin/sh"]
  RUN ["echo", "I don't use a shell at all"]
  

[ghost]

I know I am late to the party and yes this isn't the best solution, but it worked for what I needed

In my docker file after downloading and extracting the SDK I run these two commands

RUN cp /bin/bash /bin/sh
RUN echo "source ~/google-cloud-sdk/path.bash.inc" >> ~/.bashrc
RUN source ~/.bashrc

After that the gcloud command is available during the build and at run time

[qhaas]

For those interested in strict OCI reproducibility, the Dockerfile call SHELL doesn't seem to be in the OCIv1 specification, per podman 1.4:

STEP 2: SHELL ["/bin/bash", "-c"]
ERRO[0000] SHELL is not supported for OCI image format, [/bin/bash -c] will be ignored. Must use docker format

Update: Looks like thaJeztah is correct, some discussion regarding supporting this feature over at buildah: https://github.com/containers/buildah/issues/507

Update2: BUILDAH_FORMAT=docker to the rescue

[thaJeztah]

@qhaas don't think that has to do with OCI specifications, just the buildah implementation