Is the SHELL environment variable available for jobs running on Ubuntu hosts

[debarshiray]

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I am trying to run the Toolbx test suite through a GitHub Actions workflow on Ubuntu 22.04 hosts. It looks as if the SHELL environment variable is mysteriously missing in some cases.

I added a Debug step to the beginning of the job to illustrate this:

name: ubuntu-tests

on:
  pull_request:
    branches:
      - main
  schedule:
    - cron: '0 0 * * *'

jobs:
  ubuntu-jammy-tests:
    runs-on: ubuntu-22.04

    steps:
      - name: Debug
        run: |
          echo "$SHELL"
          env | grep SHELL
          useradd --defaults
          cat /proc/$$/cmdline

      - name: Checkout
        uses: actions/checkout@v3

...
...

It produces:

/bin/bash
POWERSHELL_DISTRIBUTION_CHANNEL=GitHub-Actions-ubuntu22
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=no
/usr/bin/bash-e/home/runner/work/_temp/a030d627-edc2-4e52-ad17-539ed85a4577.sh

So, echo $SHELL leads to /bin/bash, but SHELL is absent from the output of env(1), and /proc/$$/cmdline confirms that I am indeed using Bash. For what it's worth, it seems like processes spawned from the job don't have SHELL set in their environments either.

Is this expected? Do the GitHub Actions workflows do something special to the SHELL environment variable?

I am struggling to come up with the right keywords for searching because the phrase SHELL environment variable is often used to mean any environment variable instead of specifically SHELL.

[debarshiray]

/cc @HarryMichal

[debarshiray]

Ping. I still see the same behaviour.

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[debarshiray]

For what it's worth, I ended up working around it by explicitly setting the SHELL environment variable:

  env:
    SHELL: /bin/bash

I would still like to know why this is happening in the first place.

[github-actions[bot]]

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