General cleanup for the linux_json_api.sh

[zmrow]

• Add globals for all commonly used commands.

• Removeall hard coded paths.

• Make function variables local.

Hardcoded paths make me shudder. :). I did a little general cleanup and plan on doing a bit more.

Also, there was a mixed bag of which and command -v. Which can be a bit flaky depending on where you're running it. command -v is POSIX compliant but since your shebang is /bin/bash I used type -P

[tariqbuilds]

This is an excellent PR. Very hard to say no to cleaner, more reliable code.

Thank you.