How do you find the factorial of a number in a Bash script?

Question

In shell scripting how to find factorial of a number?

Answer 1

#!/bin/bash
counter=$1 #first argument
factorial=1
while [ $counter -gt 0 ] #while counter > 0
do
   factorial=$(( $factorial * $counter ))
   counter=$(( $counter - 1 ))
done
echo $factorial

Answer 2

I almost completely agree with Vitalii Fedorenko, I would just like paxdiablo suggests use bc, here's the code from Vitalii Fedorenko but modified to use bc.

#!/bin/bash
counter=$1
output=1
while [ $counter -gt 1 ] #while counter > 1 (x*1=x)
do
        output=$(echo "$output * $counter" | bc)
        counter=$(($counter - 1))
done
#remove newlines and '\' from output
output=$(echo "$output" | tr -d '\' | tr -d '\n')
echo "$output"
exit

This method is better because bc allows you to use strings, instead of integers, making it possible for you to calculate much bigger numbers.

I apologize if I haven't used tr correctly, I am not very familiar with it.

Answer 3

Please use this script to find factorial in Bash,

#!/bin/bash

num=$1
fact=1
for((i=1; i<=$num; i++))
do
        let fact=fact*i
done

echo "Factorial is $fact"

Answer 4

You can use:

seq -s "*" 1 10 | sed 's/*$//g' |bc

on a mac

Answer 5

echo 500 | dc -e '?[q]sQ[d1=Qd1-lFx*]dsFxp'

Answer 6

There are a number of instructive examples on Rosetta Code.

Here's one I found particularly useful:

function factorial {
  typeset n=$1
  (( n < 2 )) && echo 1 && return
  echo $(( n * $(factorial $((n-1))) ))
}