Run shellcheck in CI (mk 3)

[yamanawabi]

For issue #72

Shellcheck workflow downloads latest version from spellcheck repo. Currently, ubuntu provides 0.8.0. Latest is 0.9.0.

For try fixes:

In try line 68:
            mkdir -p "$SANDBOX_DIR"/upperdir/"$mountpoint" "$SANDBOX_DIR"/workdir"/$mountpoint" "$SANDBOX_DIR"/temproot/"$mountpoint"
                                                                         ^------^ SC2140 (warning): Word is of the form "A"B"C" (B indicated). Did you mean "ABC" or "A\"B\"C"?

Fixed issue by removing extra quotes and using curly braces with variables

In try line 73:
    export chroot_executable=$(mktemp)
           ^---------------^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                             ^-------^ SC2046 (warning): Quote this to prevent word splitting.


In try line 74:
    export try_mount_log=$(mktemp)
           ^-----------^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                         ^-------^ SC2046 (warning): Quote this to prevent word splitting.


In try line 75:
    export script_to_execute=$(mktemp)
           ^---------------^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                             ^-------^ SC2046 (warning): Quote this to prevent word splitting.

Fixed by defining the variables and then exporting them

In try line 229:
            read -p "Commit these changes? [y/N] " DO_COMMIT >&2
                 ^-- SC3045 (warning): In POSIX sh, read -p is undefined.

In try line 468:
            union_helper="$OPTARG" 
            ^----------^ SC2034 (warning): union_helper appears unused. Verify use (or export if used externally).

Added shellcheck ignores for these in the workflow. $union_helper is used in the generated script, and we're dealing with Linux here specifically, so POSIX compliance is not paramount

In try line 470:
        (h|*) usage; exit 0;;
         ^-- SC2214 (warning): This case is not specified by getopts.

Added h to getops line

[angelhof]

Great, thanks for your work! It looks good other than the minor nits that I added. No need to make a new PR, you can add new commits to this fixing the changes that I propose (than I will squash the PR into a single commit to main anyway). Once you do the changes @mgree approves it too we can merge :)

[mgree]

Just a few nits---looks good, thanks!

[yamanawabi]

Update: With getopts set to yvnhi, the shellcheck and test workflows are now passing. The explanation on colon use indicating an expected argument helped. Brainfart has been conquered.

---

Alright, so with getopts "yvni:D:U:", shellcheck passes a warning about the h being unspecified by getopts: https://github.com/yamanawabi/try/actions/runs/5528024252/jobs/10084360738

With getopts "yvnih:D:U", the following test fails:
https://github.com/yamanawabi/try/actions/runs/5527993006/jobs/10084295984

/tmp/tmp.pHKuXk34Ra: 1: /tmp/tmp.MLDTXG2vfr: foo1: not found
find: ‘standard output’: Broken pipe
find: write error
diff: bar.txt: No such file or directory
Running test_ignore_flag... non-zero ec (2)		FAIL

all other requests have been fixed up

[angelhof]

Tiny nit! Looks good otherwise, thanks for the help!

[yamanawabi]

thanks for making the fix and merging!