Digit to Word convert

#A shell script to input number (max 6 digit) and print the number in word. E.g. 1234 output : one two  three four

#! /bin/bash

echo -e "Enter number"
read myno
if [ `expr $myno : "^[0-9]\+$"` == 0 ] ; then
   echo "no number"
   exit 1
fi


myrevno=`echo $myno | rev`
mylen=`expr length $myrevno`
 if [ $mylen -le 6 ]

then

 until [ $myrevno -le 0 ]
 do
mydno=`expr $myrevno % 10`
myrevno=`expr $myrevno / 10`
 

case $mydno in

1) echo -n "one " ;;
2) echo -n "two " ;;
3) echo -n "three " ;;
4) echo -n "four " ;;
5) echo -n "five " ;;
6) echo -n "six " ;;
7) echo -n "seven " ;;
8) echo -n "eight " ;;
9) echo -n "nine " ;;
0) echo -n "zero " ;;

esac
 done
else
echo -e "Please, enter max. 6 digiit number..."

fi
echo -e ""