Example 1:         
#!/bin/bash 
     COUNTER=20
     until [  $COUNTER -lt 10 ]; do
        echo COUNTER $COUNTER
        let COUNTER-=1
     done
         
Example 2:
#!/bin/bash        
          if [ -z "$1" ]; then 
              echo usage: $0 directory
              exit
          fi
          SRCD=$1
          TGTD="/var/backups/"
          OF=home-$(date +%Y%m%d).tgz
          tar -cZf $TGTD$OF $SRCD