Fix SC2155 where shellcheck warns about errors

What does this MR do?

Fix linting errors (Shellcheck)

Why was this MR needed?

To solve issue #3663 (closed)

Are there points in the code the reviewer needs to double check?

• Eyeball the variable names, to ensure they are all correct
• Run script to ensure that the expected output returns (script functionality doesn't change)
• Run shellcheck to ensure all issues are caught

Does this MR meet the acceptance criteria?

• Documentation created/updated - No need, it's a "noop" change
• Added tests for this feature/bug - No need, there are no new features. May be linting needs to be added to CI, but I don't know Gitlab's policy around this.
• In case of conflicts with master - branch was rebased - No need, branched off master recently.

What are the relevant issue numbers?

Fixes #3663 (closed)