logo codesdope

Modules and Packages in Perl


A Perl package is a collection of code and a Perl module is a package defined in a file with the same name as that of the package name and having the .pm extension. A package lives in its own namespace. It means that two different modules may contain a function or a variable of the same name.

Declaring a Perl module


We use package to define a package in a module. A module name is same as that of the package name and has .pm extension. A module returns a true value to the Perl interpreter. This is explained after the following example. Let's declare a Perl module.

#File name is p.pm

use strict;
use warnings;

#Declaring package p
package p;

sub Hello{
  print "Hello\n";
}

1;

Here, the name of the file is "p.pm" and the name of the package is p. Notice that 1; is written at the end of the code. This will return a true value to the interpreter as mentioned above. We can write anything which is true in Perl instead of 1.

Using a Perl module


To use a module, we use require or use functions. We use :: to access a function or a variable from a module. Let’s look at this using an example:

#p.pm is defined in parent directory
#Filename have .pl extension

use strict;
use warnings;

#using package p
use p;

#Function Hello of p
p::Hello();
Output
Hello

Modules in different directory


If a module is present in some sub-directory, then also we use :: to tell the path of the module. For example, if a module 'b' is present in a sub-directory 'a', then we use use a::b; to load the module b. Let's see an example to understand this:

#p.pm is defined in directory ab which
#is in parent directory

use strict;
use warnings;

#using package p
use ab::p;

#Function Hello of p
p::Hello();
Output
Hello

Using variable from modules


We can also use variables from different packages. But we need to declare them first before using them. We do this by use vars qw($scalar @array %hash) and we can also use our ($scalar @array %hash) with Perl v5.6.0 or higher versions. Let's use it in an example:

#This is p.pm

use strict;
use warnings;

package b;

our ($var_name);

sub Hello{
  print "Hello $var_name\n";
}

1;
#p.pm is in parent directory

use strict;
use warnings;

#using package p
use p;

#using var_name from p
$p::var_name = "Sam";
#Function Hello of p
p::Hello();
Output
Hello Sam

BEGIN and END


BEGIN and END is used when we want to run some piece of code at the beginning and some at the end. The codes written within BEGIN{...} are executed at the beginning of the script and codes written within END{...} are executed at the end of the script. Let's see an example of this.

use strict;
use warnings;

BEGIN{
  print "Starting...\n";
}
END{
  print "END OF PROGRAM\n";
}

print "Hello World;\n";
Output
Starting...
Hello World;
END OF PROGRAM

Export and import of functions


We can make any function defined in a package for direct use by using Exporter. We just have to write:

use Exporter;

use vars qw(@ISA @EXPORT);

@ISA=qw(Exporter);

@EXPORT=(function1, function2);

We have used Exporter module and then @EXPORT array to export the functions. Let's see an example:

#p.pm

package p;

use strict;
use warnings;

use Exporter;

use vars qw(@ISA @EXPORT);

@ISA=qw(Exporter);

@EXPORT=("Hello");

sub Hello{
  print "Hello\n";
}
use strict;
use warnings;

use p;
Hello();
Output
Starting...
Hello World;
END OF PROGRAM

As you can see that here we have directly used the function 'Hello'.


Download Our App.
BlogsDope App
Get it on Google Play
Doubt? Ask question
Close

Welcome.please sign up.

Close

Welcome.please login.