Shell Script to Find Factorial of a Number

Method 1:
#!/bin/bash
# fact1
# Finding factorial of a given number
#

echo "Enter a number"
read num
fact=1
n=$num
while [ $num -ge 1 ]
do

  fact=`echo $fact \* $num|bc`
  
  # You can use bellow commands also 
  # fact=$((fact*num))
  # fact=`expr $fact \* $num`
  # But maximum integer value that bash can handle is 
  # 9223372036854775807.
  # An  operation  that takes a variable  outside these 
  # limits  will give an erroneous result. To solve this
  # problem store numbers as strings and use bc for math.
  
  let num--

done
echo "factorial of $n is $fact"

Method 2:
#!/bin/bash
# fact2
# Usage : sh fact2 Number

factorial ()  
{
local number=$1
if [ $number -eq 0 ]
then
    Factorial=1
else
    let "next = number - 1"
    factorial $next
    Factorial=`echo $number \* $Factorial | bc`
#   let "Factorial = $number * $Factorial"
fi
return $Factorial 2>/dev/null
}

# Bash function returns integer value only.
# But maximum integer value that bash can handle is 
# 9223372036854775807.
# An operation that takes a variable outside these limits 
# will give an erroneous result. That's why I redirected 
# stderror output to /dev/null

# Main program starts here.
if [ $# -ne 1 ]
then
    echo "Invalid Arguments"
    echo "Usage: ./fact2.sh  Number "
    exit 1
fi
factorial $1
echo "Factorial of $1 is $Factorial"

Output:
[root@localhost shell]# ./fact1
Enter a number
8 
factorial of 8 is 40320
[root@localhost shell]# ./fact1
Enter a number
23
factorial of 23 is 25852016738884976640000

[root@localhost shell]# ./fact2 
Invalid Arguments
Usage: ./fact2.sh  Number 
[root@localhost shell]# ./fact2 7
Factorial of 7 is 5040
[root@localhost shell]# ./fact2 33
Factorial of 33 is 8683317618811886495518194401280000000