Shell program to read a number and reverse the number

#!/bin/bash
# Shell program to read a number and reverse the number
# for example 123 should output as 321
# -----------------------------------------------
# Copyright (c) 2005 nixCraft project <http://cyberciti.biz/fb/>
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
 
echo -n "Enter number : "
read n
 
# store single digit
sd=0
 
# store number in reverse order
rev=""
 
# store original number
on=$n
 
# use while loop to caclulate the sum of all digits
while [ $n -gt 0 ]
do
    sd=$(( $n % 10 )) # get Remainder 
    n=$(( $n / 10 ))  # get next digit
    # store previoues number and current digit in rev
    rev=$( echo ${rev}${sd} ) 
done
 
echo  "$on in a reverse order $rev"