Add shellcheck step to PR process.

[trackleft]

Motivation

It would be good to find errors in our bash script files before updating the main branch.

Is your feature request related to a problem? Please describe.

This is more of a prevention step to make it easier for non bash experts to contribute bash scripts to the project.

Proposed Resolution

Use something similar to this.

name: Pull request checks
on: pull_request

jobs:
  lint-bash:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v1
      - name: Run ShellCheck
        uses: azohra/[email protected]
        with:
          exclude-paths: Dockerfile, .github/CODEOWNERS, .github/ISSUE_TEMPLATE

[mmunro-ltrr]

One extra comment (going here, but applies to the analogous issues in other repositories): we might want to promote a more generic shell than Bash! Particularly now that it isn't the default shell on MacOS, but there are minor efficiencies in going with some other shells in particular cases (this made a difference to runtimes for git under Linux). The Debian Linux distribution actually deprecated the use of Bash in favor of a generic POSIX shell (with support for local variables the only non-standard feature). The only thing that's been more difficult to work around after avoiding bash has been the failure status of chains of piped commands.

See
az-digital/az-digital-devops#3
az-digital/az-icons#28
az-digital/arizona-bootstrap#465
az-digital/az-quickstart-pantheon#85
az-digital/az-quickstart-scaffolding#63

[trackleft]

Should we add the following from the docs?
https://github.com/marketplace/actions/shellcheck#shellcheck-options

      env:
        SHELLCHECK_OPTS: --shell sh

[-s](https://www.mankier.com/1/shellcheck#-s) shell, --shell=shell
Specify Bourne shell dialect. Valid values are sh, bash, dash and ksh. The default is to deduce the shell from the file's shell directive, shebang, or .bash/.bats/.dash/.ksh extension, in that order. sh refers to POSIX sh (not the system's), and will warn of portability issues.

[mmunro-ltrr]

@trackleft : the option to deduce it from the files is nicer (particularly when it can follow the shebang line, which makes it easy to change the shell actually used by script files). That way it can check Bash-specific details for scripts that still need it, but still complain about Bashisims in generic shell scripts.