Learning Perl Objects, References, and Modules

Chapter 12. Using Modules

A module is a building block for your program: a set of related subroutines and variables packaged so it can be reused. This chapter looks at the basics of modules: how to bring in modules that others have written, and how to write modules of your own.

Sample Function-Oriented Interface: File::Basename

To understand what happens with use, look at one of the many modules included with a normal Perl distribution: File::Basename. This module parses file specifications into useful pieces in a mostly portable manner. The default usage:

use File::Basename;

introduces three subroutines, fileparse, basename, and dirname,^[60] into the current package: typically, main in the main part of your program. From this point forward, within this package, you can say: ^[61]

my $basename = basename($some_full_path);
my $dirname = dirname($some_full_path);

as if you had written the basename and dirname subroutines yourself, or (nearly) as if they were built-in Perl functions.^[62]

However, suppose you already had a dirname subroutine? You’ve now overwritten it with the definition provided by File::Basename! If you had turned on warnings, you’d see a message stating that, but otherwise, Perl really doesn’t care.

Selecting What to Import

Fortunately, you can tell the use operation to limit its actions. Do this by specifying a list of subroutine names following the module name, called the import list:

use File::Basename ("fileparse", "basename");

Now define the two given ...