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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (0c18028) 70.41% compared to head (68e66ad) 70.41%.

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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