Feedback please: Code quality checks of scripts

Running shellcheck to check the code quality of the scripts in the script directory result in over 580 code quality issues across 12 scripts. These issues can have unintended consequences that will result in problems with the execution of the various scripts.

[test.txt](https://github.com/githubtraining/training-manual/files/2793472/test.txt)
(rename test.txt to test or test.bash, make executable, run; requires shellcheck - See https://github.com/koalaman/shellcheck)

I'm willing to undertake this issue and resolve the code quality issues if it is considered valuable.

Feedback please.