#! /bin/bash

   myvar=0

   while [ $myvar -ne 20 ]

   do

           echo $myvar

           myvar=$(( $myvar + 1 ))

   done

Now my mind can wrap itself around everything in this script except for tis line:

  

   myvar=$(( $myvar + 1 ))

Where my difficulty arises is why the '$' before the '(('?

(it was geast fun running that script with a minus sign instead!)