What is Packages in Perl?

In this article, we will learn Packages in Perl,This free Perl tutorial for complete beginners will help you learn Perl from scratch.

Packages in Perl

Perl | Modules

Perl | Decision Making (if, if-else, Nested–if, if-elsif ladder, unless, unless-else, unless-elsif)

A Perl package is a collection of code which resides in its own namespace. Perl module is a package defined in a file having the same name as that of the package and having extension .pm. Two different modules may contain a variable or a function of the same name. Any variable which is not contained in any package belongs to the main package. Therefore, all the variables being used, belong to the ‘main’ package. With the declaration of additional packages, it is maintained that variables in different packages do not interfere with each other.

Declaration of a Perl Module

Example : Calculator.pm

package Calculator; 
  
# Defining sub-routine for Addition 
sub addition 
{ 
    # Initializing Variables a & b 
    $a = $_[0]; 
    $b = $_[1]; 
      
    # Performing the operation 
    $a = $a + $b; 
      
    # Function to print the Sum 
    print "\n***Addition is $a"; 
} 
  
# Defining sub-routine for Subtraction 
sub subtraction 
{ 
    # Initializing Variables a & b 
    $a = $_[0]; 
    $b = $_[1]; 
      
    # Performing the operation 
    $a = $a - $b; 
      
    # Function to print the difference 
    print "\n***Subtraction 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.

Using a Perl Module

Examples: Test.pl

#!/usr/bin/perl 
  
# Using the Package 'Calculator' 
use Calculator; 
  
print "Enter two numbers to add"; 
  
# Defining values to the variables 
$a = 10; 
$b = 20; 
  
# Subroutine call 
Calculator::addition($a, $b); 
  
print "\nEnter two numbers to subtract"; 
  
# Defining values to the variables 
$a = 30; 
$b = 10; 
  
# Subroutine call 
Calculator::subtraction($a, $b); 

Output:

Accessing a Package from a different directory

Examples: Test_out_package.pl outside Calculator directory

#!/usr/bin/perl 
  
use GFG::Calculator; # Directory_name::module_name 
  
print "Enter two numbers to add"; 
  
# Defining values to the variables 
$a = 10; 
$b = 20; 
  
# Subroutine call 
Calculator::addition($a, $b); 
  
print "\nEnter two numbers to subtract"; 
  
# Defining values to the variables 
$a = 30; 
$b = 10; 
  
# Subroutine call 
Calculator::subtraction($a, $b); 

Output:

Using Variables from modules

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 = "ABC"; 
  
# Subroutine call 
Message::Hello(); 

Output:

Begin and End Block

Examples: begineg.pl

#!/usr/bin/perl 
  
# Predefined BEGIN block 
BEGIN 
{ 
    print "In the begin block\n"; 
} 
  
# Predefined END block 
END 
{ 
    print "In the end block\n"; 
} 
  
print "Hello Perl;\n"; 

Output:

In the begin block
Hello Perl;
In the end block

Tags:

#Perl

Perl | Modules

Perl | Decision Making (if, if-else, Nested–if, if-elsif ladder, unless, unless-else, unless-elsif)