Let's Talk About SAX - Perl

Converted your little black book into XML, and don't know what to do next? This article gets you started on the path to being an XML guru, demonstrating how to use Perl's SAX parser to parse and convert your XML into Web-friendly HTML.

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By: icarus, (c) Melonfire

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January 15, 2002

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TOOLS YOU CAN USE

The first of these approaches is SAX, the Simple API for XML. A SAX parser works by traversing an XML document and calling specific functions as it encounters different types of tags. For example, I might call a specific function to process a starting tag, another function to process an ending tag, and a third function to process the data between them.

The parser's responsibility is simply to parse the document; the functions it calls are responsible for processing the tags found. Once the tag is processed, the parser moves on to the next element in the document, and the process repeats itself.

Perl comes with a SAX parser based on the expat library created by James Clark; it's implemented as a Perl package named XML::Parser, and currently maintained by Clark Cooper. If you don't already have it, you should download and install it before proceeding further; you can get a copy from CPAN (http://www.cpan.org/).

I'll begin by putting together a simple XML file:

<?xml version="1.0"?>
<library>
<book>
<title>Dreamcatcher</title>
<author>Stephen King</author>
<genre>Horror</genre>
<pages>899</pages>
<price>23.99</price>
<rating>5</rating>
</book>
<book>
<title>Mystic River</title>
<author>Dennis Lehane</author>
<genre>Thriller</genre>
<pages>390</pages>
<price>17.49</price>
<rating>4</rating>
</book>
<book>
<title>The Lord Of The Rings</title>
<author>J. R. R. Tolkien</author>
<genre>Fantasy</genre>
<pages>3489</pages>
<price>10.99</price>
<rating>5</rating>
</book>
</library>

Once my data is in XML-compliant format, I need to decide what I'd like the final output to look like.

Let's say I want it to look like this:

As you can see, this is a simple table containing columns for the book title, author, price and rating. (I'm not using all the information in the XML file). The title of the book is printed in italics, while the numerical rating is converted into something more readable.

Next, I'll write some Perl code to take care of this for me.

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