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MissingShell

Run step is missing a shell.

Defined by MissingShellRule which supports workflows in the "Default" ruleset.

Description

Specifying a shell explicitly has benefits, see the shell: documentation for what changes.

The shell: can be specified on 3 levels, and the lowest wins:

For Linux / macOS runners it's recommended to specify bash explicitly, because it adds additional arguments:

  • -e: to stop on first error (used for both)
  • -o pipefail: propagate exit code from error inside a pipe
  • --noprofile/--norc start with a clean environment.

For a deeper explanation of -e/-o read this gist. This gives us faster failures and more useful error messages.

It's worth noting that simple shell commands might not warrant an explicit shell, but it's worth adding them anyway:

  • for consistency with other steps and workflows.
  • for maintainability, in case the command becomes more complex, protection is already in place.
  • for copy-paste-ability, when the command or its modified version is "reused" in other workflows.
  • for readability, to help the reader understand the environment the script is running in.

Known shortcut: shell: bash is also recommended for Windows, but it's supported by GitHub Actions.

Compliant examples

Compliant example #1

Specified shell makes grep fail.

example.yml 

on: push
jobs:
  example:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Example" | grep "Missing" | sort
        shell: bash

Compliant example #2

Globally specified shell is inherited to the step.

example.yml 

on: push
jobs:
  example:
    runs-on: ubuntu-latest
    defaults:
      run:
        shell: bash
    steps:
      - run: echo "Example" | grep "Missing" | sort

Non-compliant examples

Non-compliant example #1

Missing shell masks pipe failures.

example.yml 

on: push
jobs:
  example:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Example" | grep "Missing" | sort

  • Line 6: Step[#0] in Job[example] is missing a shell, specify bash for better error handling.

Non-compliant example #2

Shell is mandatory for composite action steps.

example.yml 

name: Test
description: Test
runs:
  using: composite
  steps:
    - run: echo "Example" | grep "Missing" | sort