Calculate Factorial of a Number

Time to practice your Bash scripting.

Exercise

In this Bash practice exercise, write a shell script that accepts a non-negative number and shows its factorial as output.

💡Hint: Factorial is calculated in this fashion:

N! = N x (N-1) x (N-2) x (N-3) x ... x 3 x 2 1 

Remember that the factorial of 0 is 1. And you cannot have a factorial of negative numbers.

Test data

If you input 5, you should get the following (5 x 4 x 3 x 2 x 1):

120

If you input 7, you should get the following:

5040

Solution 1: Factorial bash script using recursive function

Here's a sample bash scripting for getting factorial of a given number using only a for loop.

I have added the option step for checking that non-negative numbers are not enetered.

#!/bin/bash

read -p "Enter a non-negative number: " num

if [ $num -lt 0 ]; then
	echo "You entered a negative number"
	exit
fi

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

echo "$num! is: $fact"

Solution 2: Factorial script using factorial in bash

Here's a bash shell script that uses the concept of recursion and function:

#!/bin/bash

read -p "Enter a non-negative number: " num

if [ $num -lt 0 ]; then
	echo "You entered a negative number"
	exit
fi

factorial () {
	if [ $1 -le 1 ]; then
		echo 1
	else
	last=$(factorial $(( $1 -1)))
		echo $(( $1 * last ))
	fi
}

echo -n "$num! is: "
factorial $num

📖 Concepts to revise

The solutions discussed here use some terms, commands and concepts and if you are not familiar with them, you should learn more about them.

• read command
• arithmetic operation in bash
• if else in bash
• for loop in bash
• functions in bash

📚 Further reading

If you are new to bash scripting, we have a streamlined tutorial series on Bash that you can use to learn it from scratch or use it to brush up the basics of bash shell scripting.

Bash Scripting Tutorial Series for Beginners [Free]

Get started with Bash Shell script learning with practical examples. Also test your learning with practice exercises.

Linux HandbookAbhishek Prakash