Perl Module Basics

Modules

Modular programming requires two facilities in a programming language 

encapsulation and interfaces. Packages provide encapsulation by furnishing 

separate namespaces for subroutines and variables. Modules are Perl's facility for 

providing packages with interfaces. In actuality, Perl's support for interfaces are a 

set of conventions around the use of packages and module filenaming. There is no 

module keyword

6

 and no extra syntax to learn.

You tell Perl your module s name in two ways first, by naming the module file. 

The filename corresponds to the module name by replacing the :: marks with file 

system separators and appending a .pm extension to the end. For example, here are 

some module names and their associated filenames on UNIX and Windows systems:

Table 2 1. Examples of Module Names Converted to Filenames on UNIX and 

Windows systems

Module Name

UNIX Filename

Windows Filename

CGI

CGI.pm

CGI.pm

HTML::Template

HTML/Template.pm

HTML\Template.pm

Scalar::List::Utils

Scalar/List/Utils.pm

Scalar\List\Utils.pm

Secondly, at the top of your module file you declare the name in a package line:

package Hello;

sub greet {

   my $name = shift;

   print "Hello, $name!\n";

}

1;

TIP Perl modules must end by with a true statement. This tells Perl 

that your module compiled successfully. Leaving off the true statement 

will result in a compilation error.

6. At least not yet! Early Perl 6 designs include mention of a new keyword for modules and 

classes separate from normal packages.

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