Recursion in Perl

• Last Updated : 27 Jun, 2021

Recursion is a mechanism when a function calls itself again and again till the required condition is met. When the function call statement is written inside the same function then such a function is referred to as a recursive function.
The argument passed to a function is retrieved from the default array @_ whereas each value can be accessed by \$_, \$_ and so on.
Example 1: The example below finds factorial of a number.

Factorial of any number n is (n)*(n-1)*(n-2)*....*1.
e.g.:
4! = 4*3*2*1 = 24
3! = 3*2*1 = 6
2! = 2*1 = 2
1! = 1
0! = 0

Perl

 #!/usr/bin/perl # Perl Program to calculate Factorialsub fact{     # Retrieving the first argument# passed with function callingmy \$x = \$_; # checking if that value is 0 or 1if (\$x == 0 || \$x == 1){    return 1;} # Recursively calling function with the next value# which is one less than current oneelse{    return \$x * fact(\$x - 1);}} # Driver Code\$a = 5; # Function call and printing result after returnprint "Factorial of a number \$a is ", fact(\$a);

Here is how the program works :
Step 1- When the value of scalar a is 0 or 1, the function will return 1 because the value of both 0! and 1! is 1.
Step 2- When the value of scalar a is 2 then fac(x-1) makes a call to fac(1) and this function returns 1.
So, it is 2*factorial(1) = 2*1 = 2.So, it will return 2.
Step 3- Similarly when higher values are passed to function at every call argument value decreases by 1 and computes till the value reaches 1.
Example 2: Example below computes the Fibonacci series till a given number.

Perl

 #!/usr/bin/perl # Perl Program to print Fibonacci seriessub fib{    # Retrieving values from the parameter    my \$x = shift;    my \$y = shift;         # Number till which the series is to be printed    my \$n = shift;         # Check for the end value    if (\$y > \$n)    {        return 1;    }         # Printing the number    print " \$y";     # Recursive Function Call    fib(\$y, \$x + \$y, \$n);    } # Driver Code # Number till which series is to be printed\$a = 5; # First two elements of the series\$c = 0;\$d = 1; print "\$c"; # Function call with required parametersfib(\$c, \$d, \$a);

Here is how the program works :
Step 1- Function fib() is called with 3 parameters starting values which will be 0 and 1 while \$n is a number till which a series is to be printed
Step 2- These values are transferred in the form of an array whose values are retrieved with the use of shift.
Step 3- At each call first two values are retrieved using shift and these values are stored in scalars x and y. Now these two values are added to get the next value in the series. This step continues till the value reaches the ending value provided by the user

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