Mastering Linux Shell Scripting - Second Edition

Recursive functions

A recursive function is a function that calls itself from inside itself. This function is very useful when you need to call the function to do something again from inside of it. The most famous example for that is calculating factorials.

To calculate the factorial of 4, you multiply the number by the descending numbers. You can do it like this:

4! = 4*3*2*1

The ! sign means factorial.

Let's write a recursive function that calculates the factorial of any given number:

#!/bin/bash calc_factorial() { if [ $1 -eq 1 ] then echo 1 else local var=$(( $1 - 1 )) local res=$(calc_factorial $var) echo $(( $res * $1 )) fi } read -p "Enter a number: " val factorial=$(calc_factorial $val) echo "The factorial of $val is: $factorial" ...