Processing Text with Perl Modules - Page 11

The Power of CPAN

The Comprehensive Perl Archive Network is a group of servers around the world that provide access to the Perl source code and hundred of Perl modules that have been contributed by volunteers. CPAN is one of the things I imagine other language authors wish they had for their respective languages (like Java) but don't. Fortunately for us, pre-built modules that bundle up the code and logic for performing many common tasks are freely available for the taking. See the list of resources on the last page of this article for a list of resources.

Installing Modules

Part of what makes CPAN powerful is the fact that Perl supports it directly with the CPAN.pm module, which has been distributed with the Perl source code for several years now. The module is capable of searching for, downloading, and installing modules directly from CPAN. It will even handle module dependencies where the module you're trying to install requires other modules from CPAN before it can be installed.

On most operating systems, you can install a CPAN module by typing:

perl -MCPAN -e 'install HTML::Parser'

where HTML::Parser is the name of the module you wish to install. This will automatically find, download, compile, and install the module onto your system.

If you are using Activestate Perl and the module you are installing is available in Activestate's repository, you can type: ppm install GD

PPM is a command-line utility that is only available if you are using Activestate Perl. Note that not all Perl modules from CPAN are available to PPM. So if you're running Activestate Perl on a win32 platform, you will also need to have Visual C++ and nmake installed on your system to load modules from CPAN that are not available to PPM.

Making Text HTML Safe

I'm sure most of you have had at least one occasion where you needed to effectively cut and paste a text file into an HTML file. If that text file contained any reserved characters like & or <, you probably had to convert them to HTML-safe entities such as < for < by hand. Or maybe you haven't fixed the text and you now have an invalid HTML document out there on your Web site.

Well, if you find yourself doing this hand tuning on a regular basis or if you're routinely posting text into HTML files without checking to see if it's HTML safe, stop; because CPAN has a module called HTML::Entities which does all of the work for you.

The module contains a function appropriately named encode_entities() that automatically encodes all HTML reserved characters. So for example, if you have a string of text that's contained in a variable named $text that needs to be HTML encoded, you would first add the statement: use HTML::Entities to the top of your script and then type:

encode_entities($text);

somewhere in the main body of your source code. So if $text contained the string "Fred & Barney's Bowling Academy", it would be converted into "Fred & Barney's Bowling Academy".

We could also build a simple script that converts an entire file such that we can execute the following on the command-line:

html_encode.pl < sample.txt > newtext.txt

Or in plain english, we direct a text file called sample.txt to the script as input and write the resulting encoded text to newtext.txt. The source of the script would look like the following:

#!/usr/bin/perl -w
use strict;
use HTML::Entities;

while (<>) {
    encode_entities($_);
    print;
}

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Weaving Magic With Regular Expressions
Encrypting Text with RC4 - Page 12