Squash some shellcheck *errors*

[drwetter]

and some warnings.

One of the latter being export was a variable. It obviously worked the past years. For the sake of cleaner code I renamed those occurrences.

Five errors of type SC2145 are left as I am not sure whether it'll be safe to follow the recommendation.

@dcooper16 : Can we safely change that?

Describe your changes

Please refer to an issue here or describe the change thoroughly in your PR.

What is your pull request about?

• Bug fix
• Improvement
• New feature (adds functionality)
• Breaking change (bug fix, feature or improvement that would cause existing functionality to not work as expected)
• Typo fix
• Documentation update
• Update of other files

If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs, indentation is five spaces and any line endings do not contain any blank chars
• I've read CONTRIBUTING.md and Coding_Convention.md
• I have tested this fix or improvement against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
• For the new feature I have made corresponding changes to the documentation and / or to help()
• If it's a bigger change: I added myself to CREDITS.md (alphabetical order) and the change to CHANGELOG.md

[dcooper16]

Five errors of type SC2145 are left as I am not sure whether it'll be safe to follow the recommendation.

@dcooper16 : Can we safely change that?

Yes, I believe these can safely be changed.