Write a shell script to accept a number and compute it's factorial?

echo "Enter the number whose factorial is to be computed"

read num

temp=`expr $num - 1`

while [ $temp -ge 1 ]

do

num=`expr $num \* $temp`

temp=`expr $temp - 1`

done

echo "The factorial of number is : $num"             

OUTPUT :

Enter the number whose factorial is to be computed

5

The factorial of number is : 120