fix: change shebangs in scripts and some shellcheck fixes

[Tanish2002]

On some systems bash might not be necessarily inside /bin/bash so changed to shebangs to /usr/bin/env bash

Also performed some shellcheck fixes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.41%. Comparing base (0c18028) to head (68e66ad).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1176   +/-   ##
=======================================
  Coverage   70.41%   70.41%           
=======================================
  Files         174      174           
  Lines       27515    27515           
=======================================
  Hits        19376    19376           
  Misses       8139     8139           

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