✨ add a GitHub Action for shellcheck'ing on every PR and push to master branch + shellcheck'ed script

[thomasmerz]

shellcheck was complaining:

$ docker run --rm -v "$PWD:/mnt" koalaman/shellcheck:stable -Calways -S warning lsix

In lsix line 196:
	for x in ${!MAPFILE[@]}; do
                 ^------------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.


In lsix line 208:
		(cd "$arg"; $lsix)
                 ^-------^ SC2164 (warning): Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

Did you mean:
		(cd "$arg" || exit; $lsix)


In lsix line 218:
    resize="[${tilewidth}x${tileheight}]"
    ^----^ SC2034 (warning): resize appears unused. Verify use (or export if used externally).


In lsix line 237:
	while [ $# -gt 0  -a  $# -gt $goal ]; do
                          ^-- SC2166 (warning): Prefer [ p ] && [ q ] as [ p -a q ] is not well defined.

For more information:
  https://www.shellcheck.net/wiki/SC2068 -- Double quote array expansions to ...
  https://www.shellcheck.net/wiki/SC2034 -- resize appears unused. Verify use...
  https://www.shellcheck.net/wiki/SC2164 -- Use 'cd ... || exit' or 'cd ... |...

This PR fixed this and I tested it:

My GitHub Action's Run can be found here.

[thomasmerz]

@hackerb9 , I have rebased and my PR is ready for your assessment…
It should be clear which shellcheck warnings and errors are fixed (I didn't care about infos and style) and that this PR introduces a free of charge GitHub Action that will shellcheck every push to master or any PR.

[hackerb9]

Oog. That's ugly. lsix is supposed to be a simple script that people can easily hack upon without all the extra cognitive load of these sort of distractions.

How about just adding the GitHub Action so it can run as an advisory linter but leave all these shellcheck comments out of the code?

[thomasmerz]

These comments are neccessary for shellcheck so it won't complain about a specific error or warning in the next line. So for bash-hackers it should not confuse or distract them - but a failing shellcheck GitHub Action might confuse 🤔
I tried to fix this as mentioned/hinted on https://github.com/koalaman/shellcheck/wiki/SC2068 - but then lsix failed doing the right thing 😞 So I left shellcheck intentionally ignore this because it works/does the right thing.

[thomasmerz]

I added a comment that should help other users understand why these shellcheck-lines are neccessary. And I fixed (cd "$arg"; $lsix) to (cd "$arg" && $lsix) - Do you @hackerb9 agree to that?