Cleanup: Apply new script practices.

Cleanup: Apply new script practices.

This is essentially a backport of the 0.7 commit f856496d258a223eb7eb5f8fe645297e8af27b46.

Be more consistent about wrapping all variables in brackets.
This helps make the code more consistent and also more compatible with other interpreters like ZSH.

Don't use echo pipe syntax and instead use "<<<" redirection pipe syntax for passing variables to program calls.

The grep commands should use either `-sho` or `-shoP`.

Add missing 'unset main' calls in some scripts.

Several of the level_3 program scripts are skipped from these changes.
I simply did not want to spend the time migrating those.