Refactor Shell Scripts based on ShellCheck's suggestion

[PeterDaveHello]

This will help improve the robustness of the scripts, some of the deprecated and non-safe statements need to be refactored.

[Changaco]

Thanks but I'm not going to merge this as-is. The changes seem mostly unnecessary, and some of them are in obsolete files that I should have deleted months ago.

[PeterDaveHello]

I can revert the changes on files need to be deleted. I don't think they are all that unnecessary, for example, one of their header used #!/bin/sh which may not support many of statements in the script, and -o/-a in bash condition were deprecated for a while, it's no hurt to have these changes, they only make those scripts less potential of issues.

[chadwhitacre]

Merging the changes to the obsolete files makes no difference since the files are obsolete anyway.

Merging the unnecessary changes probably(?) won't hurt.

I agree that @PeterDaveHello's PRs such as this one tend to be low-value, but ¯\_(ツ)_/¯. Seems best to either merge or close to keep the PR queue moving.

[Changaco]

Rebased on master and added a commit to delete the obsolete files.

[Changaco]

And another to revert changes that weren't merely unnecessary but invalid.

[chadwhitacre]

I don't know how the double quotes behave here.

[Changaco]

This is quite common in shell scripts, I think it works as intended.

[chadwhitacre]

Assuming those double double quotes lines work as intended, lgtm.