Chapter 2

This chapter will explain Perl's support for modular programming and delve into 

modular programming's funny looking cousin, object oriented programming. You 

may want to skip this chapter if you have experience programming modules in Perl.

Using Modules

Using modules in Perl is extremely easy. Simply place a use statement at the top of 

your program specifying the name of the module. For example, here's a program 

that lists all the files over 1 megabyte in size below the current directory, using the 

File::Find module that comes with Perl:

#!/usr/bin/perl

use File::Find;

find(sub { print "$_\n" if  s $_ > 1_024_000; }, ".");

The File::Find module provides the find() function that traverses directories. 

For every file it finds, it calls the subroutine you pass as the first argument. The 

name of the current file is made available in the $_ variable. In the preceding 

example the subroutine examines the size of the file using  s and prints its name if 

the size is over a megabyte.

You could, of course, write this program without using File::Find. However, it 

would certainly be much longer than the two lines required to do the job with 

File::Find. File::Find, like many modules, makes your life easier by providing you 

with functionality that you can use without having to write it yourself. Like most 

modules, File::Find provides documentation in POD format (covered in detail in 

Chapter 3). You can read this documentation using perldoc:

1

$ perldoc File::Find

File::Find provides its functionality through the find() function. This function 

is exported. Exporting means that the module provides access to a symbol,

2

 in this 

case the find() subroutine, in the namespace where the module is used. I'll cover 

exporting in more depth later in this chapter.

1.  UNIX users may also be able to use man to read module documentation. This is generally 

faster than using perldoc.

2.  Symbol  is a fancy word for named things in Perl. Variables, subroutines, and file handles 

are all  symbols. 

22