How to de-bug the shell script?

• While programming shell sometimes you need to find the errors (bugs) in shell script and correct the errors (remove errors - debug).
• For this purpose you can use -v and -x option with sh or bash command to debug the shell script. Syntax:

  sh option { shell-script-name }
  OR
  bash option { shell-script-name }
  Option can be
  -v Print shell input lines as they are read.
  -x After expanding each simple-command, bash displays the expanded  
     value of system variable,followed by the command and its expanded
      arguments.
  

  Example; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/dsh1dsh1

  #!/bin/sh
  #
  # Script to show debug of shell
  #
  tot=`expr $1 + $2`
  echo $tot
  

  execute as

  $ ./dsh1 4 5
  9
  $ sh -x dsh1 4 5
  ++ expr 4 + 5
  + tot=9
  + echo 9
  9
  $ sh -v dsh1 4 5
  #!/bin/sh
  #
  # Script to show debug of shell
  #
  tot=`expr $1 + $2`
  expr $1 + $2
  echo $tot
  9