Perl Subroutine Tutorial and examples

The subroutine is also called a function that takes inputs executes a sequence of a code block of statements and returns the output.

Subroutines are used and created when multiple code statements want to repeatedly execute in different places.

It helps code reusability and clean separation of code in logic and features.

In this tutorial, Learn

subroutine definition
subroutine return type
subroutine parameters

How to create and define subroutines in Perl

a subroutine can be created with the keyword sub, followed by the name of the subroutine and the body enclosed in {}.

The subroutine contains the following syntax.

sub subroutine_name{
    //body contains code block;
}

subroutine_name: Name of the Subroutine. the body is a Perl code statement that executes in sequential order the subroutine body is enclosed in {}

Once the above code is defined, The subroutine is called with the below syntax. Subroutine Invocation syntax:

subroutine_name(arguments);

subroutine_name: Subroutine name executed arguments: parameters to the subroutine.

Here is a simple function definition.

## Check number is positive or not
sub negative
{
    # Get the given number
    $number = $_[0];

    if($number<0){
    return 1;
    }
    else{
        return 0
    }
}

## Calling subroutine
print( negative(-12));

Output:

Subroutine parameters

subroutine parameters are stored in a Perl special variable @_ as an array. Perl subroutines accept any number of parameters.

printParameters(1, 2, 3, 4, 5, 6);
printParameters(1..3);
printParameters(2,13,5,8,7);
printParameters("a".."z");
sub printParameters {
 $args = @_ ;
 print("Arguments Count: $args\n");
}

Output:

Arguments Count: 6
Arguments Count: 3
Arguments Count: 5
Arguments Count: 26

You can also assign an array into scalar variables as given In the below example, subroutine arguments are assigned to individual variables, ($first, $secibd) = @_ ; called scalar assignment

add(2, 3);
sub add {
($first, $secibd) = @_ ;
 print("$first: $second\n");
}

Perl Subroutine examples types

Subroutine without arguments and return type:

This example contains a subroutine with no arguments and no return type

sub getMsg{
    print "hello";
}

getMsg();
getMsg;

Functions without arguments and has return type:

This example shows a subroutine without arguments and returns a type. return keyword used to return the control to the calling subroutine.

sub getMsg{
    return "hello";
}

print(getMsg());
print( getMsg);

subroutine with arguments and without return type: This example shows a subroutine with arguments and without return type. arguments are stored in Perl special variable $_ as an array. array values can be retrieved using an index.

## add numbers
sub add
{
    # Get Given numbers
    local $number1 = $_[0];
    local $number2 = $_[1];
   print "$number1 +$number2";

}
add(1,3);

Subroutine with arguments and return type: The below subroutine contains arguments and returns the result to the caller subroutine

## add numbers
sub add
{
    # Get the Given number
    local $number1 = $_[0];
    local $number2 = $_[1];
    my $result=$number1 +$number2;
    return $result;
}
print(add(1,3));

Nesting Subroutines

subroutines called inside another subroutine called nested subroutine. printCount() subroutine declared and called inside the same function.

printCount();
sub printCount{
 print("$index\n");
 $index++;
 if($index<5){
     printCount();
 }
}

How to declare a private function

functions are declared without a name and assigned to a Perl variable, also called subroutine expression.

calling these function using $getMessage->( $self ) syntax.

private functions per example

my $getMessage = sub {
    return  'hello world';
 };

print($getMessage->( $self ))

Subroutine Advantages

The Subroutine has advantages in Perl.

Code declared once and used and executed in multiple places, allows reusability
Code separation into feature and logic wise and enhances code
Unit testing is easy as you need to test functions only
Development and productivity is improved
Helps functions to debug and fix issues

Perl - Subroutine