Programming Perl, 4th Edition

Loading Modules

Modules come in two flavors: traditional and object-oriented. Traditional modules define subroutines and variables for the caller to import and use. Object-oriented modules function as class definitions and are accessed through method calls, described in Chapter 12. Some modules do both.

Perl modules are typically included in your program by saying:

use MODULE;

This is equivalent to:

BEGIN {
  require MODULE;
  MODULE–>import();
}

This happens during the compile phase, so any code in the module runs during the compile phase. This usually isn’t a problem since most code in modules lives in subroutines or methods. Some modules may load additional modules, XS code, and other code components. Since Perl handles a use when it runs into it, any modifications to @INC need to happen before the use. You probably want the lib pragma (see Chapter 29), which you also load with use.

If you want to load the module during the run phase, perhaps delaying its inclusion until you run a subroutine that needs it, you can use require:

require MODULE;

MODULE must be a package name that translates to the module’s file. The use translates :: to / and then appends a .pm to the end. It looks for that name in @INC. If your module is named Animal::Mammal::HoneyBadger, this will look for Animal/Mammal/HoneyBadger.pm. Once loaded, the path where Perl found the file shows up in %INC. Perl loads a file once. Before it tries to load a file, it looks in %INC to see whether it is already loaded. If so, it can ...