docker build examples wrt shell

[rcoup]

steps:
  - label: ':hammer: Build image'
    command: 
      - >
        docker build --pull
        --build-arg PIP_INDEX_URL=${PIP_INDEX_URL:-https://pip.example.net/root/dev/+simple/}
        --build-arg PIP_TRUSTED_HOST=${PIP_TRUSTED_HOST}
        -t acme/app:${BUILDKITE_BRANCH}.latest .
    plugins:
      docker#v1.4.0:
        image: "docker:stable"
        debug: true
        mounts:
          - /var/run/docker.sock:/var/run/docker.sock

Running docker build --pull --build-arg 
     PIP_INDEX_URL=${PIP_INDEX_URL:-https://pip.example.net/root/dev/+simple/}
     --build-arg PIP_TRUSTED_HOST=${PIP_TRUSTED_HOST} -t acme/app:citest.latest .
--|--
  | in docker:stable
  | $ docker run -it --rm --volume /buildkite/builds/abcdef123-1/acme/app:/workdir 
      --workdir /workdir --env BUILDKITE_JOB_ID --env BUILDKITE_BUILD_ID --volume
      /var/run/docker.sock:/var/run/docker.sock docker:stable bash -e -c docker build --pull 
      --build-arg PIP_INDEX_URL=${PIP_INDEX_URL:-https://pip.example.net/root/dev/+simple/} 
      --build-arg PIP_TRUSTED_HOST=${PIP_TRUSTED_HOST} -t acme/app:citest.latest .
  |  
  | /usr/local/bin/docker-entrypoint.sh: exec: line 35: bash: not found
  | 🚨 Error: The command exited with status 127

The docker images have busybox as sh, and no bash.

shell (optional)
Set the shell to use for the command. Set it to false to pass the command directly to the docker run command. The default is bash -e -c.

For my example setting shell: false works fine.

I wonder whether it should be sh -e -c to try and catch as many image variants as possible? The most common ${FOO:-default} etc stuff is all handled relatively consistently, even if some of the super-crazy bash'isms aren't. Or add a note to the docker build doc to say that if you need any complex stuff use shell: "sh -ec"?

[toolmantim]

Yep, we should make this change (originally mentioned it in #50 (comment) but never followed up). Probably worth a major version bump.

[lox]

We've made some pretty major changes to how we handle shells in #68 which should cover this. The new default if a command is provided is [/bin/sh, -e, -c]