Perl | Modules

A module in Perl is a collection of related subroutines and variables that perform a set of programming tasks. Perl Modules are reusable. Various Perl modules are available on the Comprehensive Perl Archive Network (CPAN). These modules cover a wide range of categories such as network, CGI, XML processing, databases interfacing, etc.

Creating a Perl Module

A modules name must be same as to the name of the Package and should end with .pm extension.

Example : Calculator.pm

package Calculator;

# Defining sub-routine for Multiplication
sub multiplication
{
    # Initializing Variables a & b
    $a = $_[0];
    $b = $_[1];

    # Performing the operation
    $a = $a * $b;

    # Function to print the Sum
    print "\n***Multiplication is $a";
}

# Defining sub-routine for Division
sub division
{
    # Initializing Variables a & b
    $a = $_[0];
    $b = $_[1];

    # Performing the operation
    $a = $a / $b;

    # Function to print the answer
    print "\n***Division is $a";
}
1;

Here, the name of the file is “Calculator.pm” stored in the directory Calculator. Notice that 1; is written at the end of the code to return a true value to the interpreter. Perl accepts anything which is true instead of 1

Importing and using a Perl Module
To import this calculator module, we use require or use functions. To access a function or a variable from a module, :: is used. Here is an example demonstrating the same:

Examples: Test.pl

#!/usr/bin/perl

# Using the Package 'Calculator'
use Calculator;

print "Enter two numbers to multiply";

# Defining values to the variables
$a = 5;
$b = 10;

# Subroutine call
Calculator::multiplication($a, $b);

print "\nEnter two numbers to divide";

# Defining values to the variables
$a = 45;
$b = 5;

# Subroutine call
Calculator::division($a, $b);

Output:

Using Variables from modules

Variables from different packages can be used by declaring them before using. Following example demonstrates this
Examples: Message.pm

#!/usr/bin/perl

package Message;

# Variable Creation
$username;

# Defining subroutine
sub Hello
{
  print "Hello $username\n";
}
1;

Perl file to access the module is as below
Examples: variable.pl

#!/usr/bin/perl

# Using Message.pm package
use Message;

# Defining value to variable
$Message::username = "Geeks";

# Subroutine call
Message::Hello();

Output:

Using Pre-defined Modules
Perl provides various pre-defined modules which can be used in the Perl programs anytime.
Such as: ‘strict’, ‘warnings’, etc.

Example:

#!/usr/bin/perl

use strict;
use warnings;

print" Hello This program uses Pre-defined Modules";

Output:

Hello This program uses Pre-defined Modules