Write script to print given numbers sum of all digit, For eg. If no is 123 it's sum of all digit will be 1+2+3 = 6.

#!/bin/bash
# Algo:
#       1) Input number n
#       2) Set sum=0, sd=0
#    3) Find single digit in sd as n % 10 it will give (left most digit)
#       4) Construct sum no as sum=sum+sd
#       5) Decrment n by 1
#       6) Is n is greater than zero, if yes goto step 3, otherwise next step
#       7) Print sum
#
if [ $# -ne 1 ]
then
    echo "Usage: $0   number"
    echo "       I will find sum of all digit for given number"
    echo "       For eg. $0 123, I will print 6 as sum of all digit (1+2+3)"
    exit 1
fi

n=$1
sum=0
sd=0
while [ $n -gt 0 ]
do
    sd=`expr $n % 10`
    sum=`expr $sum + $sd`
    n=`expr $n / 10`
done
    echo  "Sum of digit for numner is $sum"