Merge changes from topic 'shellcheck'

* changes:
  Fix SC2086 Double quote variables
  Fix SC2086 for lines 300 until EOF
  Fix SC2086 for lines 490 until EOF
  Fix SC2086 for lines 575 until EOF
  Fix SC2086 for lines 700 until EOF
  Fix SC2086 for lines 940 until EOF
  Fix SC2004 $/${} unnecessary on arithmetic vars
  Fix SC2006 backtick syntax is legacy