title: How to find out duplicate arguments in shell script
body: <p>I'm supporting below arguments to the script. I want to find out duplicate arguments when its passed and throw an error. Can you please help me. </p>
  
  <pre><code>#! /bin/sh
  VCFile=
  gCFFile=
  PW=xyzzy
  
  while test $# -gt 0 
  do
    option=$(echo $1 | tr a-z A-Z)
    case $option in
  
  (-VO)    shift
            VCfile=$1
            ;;
  (-CON)  shift
            gCFFile=$1
            ;;
  (-PASSWORD) shift
            PW=$1
            ;;
  (*)     
            print "\nerror -The command line argument $1 is invalid\n"
            print "Testscript has aborted.\n"
            exit 2  
            ;;
     esac
     shift
  done
  
  ./Install.sh -VO abc.txt -CON tt.txt - pass
  ./Install.sh -VO abc.txt -CON tt.txt -ss
  
  error -The command line argument -ss is invalid
  Testscript has aborted.
  </code></pre>
  
  <p>if running with dup parameters like below</p>
  
  <pre><code>./Install.sh -VO abc.txt -CON tt.txt -CON ta.txt -PASSWORD ABC -PASSWORD non 
  </code></pre>
  
  <p>--doesn't fail , Here I want to throw an error as duplicate options are entered.</p>