Shell script to check Armstrong number

SCRIPT:

#!/bin/bash
echo -n "Enter the nuber : "
read read_val
number=$read_val
buf1=0
buf2=0
sum=0
while [ $number -gt 0 ]
do
    buf1=`expr $number % 10`
    buf2=`expr $buf1 \* $buf1 \* $buf1`
    sum=`expr $sum + $buf2`
    number=`expr $number / 10`
   
done
if [ $sum -eq $read_val ]
then
    echo "$read_val is armstrong number"
else
    echo "$read_val not a armstrong number"
fi

OUTPUT:
(i)
Enter the nuber : 178
178 not a armstrong number
(ii)
Enter the nuber : 178
178 not a armstrong number