Perl Module Basics

This is similar to the system used by Java where class names are preceded by the 

reversed domain name of their creators. For example, Java classes written by Sun 

have names beginning with  com.sun . The intent is the same that module 

names never accidentally conflict, but the Perl system is considerably simpler 

and results in shorter names. Of course, if you'd like to create a module called 

Com::Acme::AutomaticDogCatcher module, you can.

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How Perl Finds Modules

Let's take a brief detour into Perl mechanics. You need to know how Perl finds 

modules before you can start writing your own. When Perl encounters a use statement 

during compilation, it turns the module name into a filename as described earlier in 

this chapter. For example, Scalar::List::Utils becomes Scalar/List/Utils.pm. Next, 

Perl uses the global array @INC

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 to find a list of candidate directories to look for 

Scalar/List/Utils.pm. When Perl finds a module file, it is immediately compiled. 

You can find out what your Perl's default @INC is with this command:

perl  e  print join("\n", @INC) . "\n"; 

One way to use modules is to put your modules into one of the listed direc 

tories usually one with site_perl in the name. This is what happens when you 

install a module from CPAN. Another way to use modules is to modify @INC before 

Perl starts looking for modules to include a different directory where you store 

your modules. An easy way to do that is through the use lib statement shown 

earlier. A use lib statement prepends a directory onto @INC at compile time.

For example, if you have a private modules directory in your home directory

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called modules, you could start your programs with the following:

use lib  /home/sam/modules ;

You can see the effect of this command on @INC by printing out after a use lib:

use lib  /home/sam/modules ;

print join("\n", @INC) . "\n";

8. The name @INC refers to its use as an  include  path, although using a module is rarely 

referred to as  including  the module.

9. This is a UNIX specific example since Windows (and other single user operating systems) 

don't provide a  home directory.  However, use lib works just as well on Windows as it does 

on UNIX, so the techniques should be easily adaptable.

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