title: getopts no argument provided
body: <p>how to check whether there was no required argument provided? I found that ":" option in switch case should be sufficient for this purpose, but it never enters that case (codeblock). It doesn't matter whether I put "colon-case" at the beginning or elsewhere. </p>
  
  <p>my code: </p>
  
  <pre><code>while getopts :a:b: OPTION;
  do
       case "$OPTION" in
           a)
               var1=$OPTARG
               ;;
           b)
               var2=$OPTARG
               ;;
           ?)
               exitScript "`echo "Invalid option $OPTARG"`" "5"
               ;;
           :)
               exitScript "`echo "Option -$OPTARG requires an argument."`" "5"
               ;;
           *)
               exitScript "`echo "Option $OPTARG unrecognized."`" "5"
               ;;
       esac
  done
  </code></pre>
  
  <p>THX in advance.</p>