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Chapter 1. Perl and XML

Perl is a mature but eccentric programming language that is tailor-made for text manipulation. XML is a fiery young upstart of a text-based markup language used for web content, document processing, web services, or any situation in which you need to structure information flexibly. This book is the story of the first few years of their sometimes rocky (but ultimately happy) romance.

1.1. Why Use Perl with XML?

First and foremost, Perl is ideal for crunching text. It has filehandles, "here" docs, string manipulation, and regular expressions built into its syntax. Anyone who has ever written code to manipulate strings in a low-level language like C and then tried to do the same thing in Perl has no trouble telling you which environment is easier for text processing. XML is text at its core, so Perl is uniquely well suited to work with it.

Furthermore, starting with Version 5.6, Perl has been getting friendly with Unicode-flavored character encodings, especially UTF-8, which is important for XML processing. You'll read more about character encoding in Chapter 3, "XML Basics: Reading and Writing".

Second, the Comprehensive Perl Archive Network (CPAN) is a multimirrored heap of modules free for the taking. You could say that it takes a village to make a program; anyone who undertakes a programming project in Perl should check the public warehouse of packaged solutions and building blocks to save time and effort. Why write your own parser when CPAN has plenty of parsers to download, all tested and chock full of configurability? CPAN is wild and woolly, with contributions from many people and not much supervision. The good news is that when a new technology emerges, a module supporting it pops up on CPAN in short order. This feature complements XML nicely, since it's always changing and adding new accessory technologies.

Early on, modules sprouted up around XML like mushrooms after a rain. Each module brought with it a unique interface and style that was innovative and Perlish, but not interchangeable. Recently, there has been a trend toward creating a universal interface so modules can be interchangeable. If you don't like this SAX parser, you can plug in another one with no extra work. Thus, the CPAN community does work together and strive for internal coherence.

Third, Perl's flexible, object-oriented programming capabilities are very useful for dealing with XML. An XML document is a hierarchical structure made of a single basic atomic unit, the XML element, that can hold other elements as its children. Thus, the elements that make up a document can be represented by one class of objects that all have the same, simple interface. Furthermore, XML markup encapsulates content the way objects encapsulate code and data, so the two complement each other nicely. You'll also see that objects are useful for modularizing XML processors. These objects include parser objects, parser factories that serve up parser objects, and parsers that return objects. It all adds up to clean, portable code.

Fourth, the link between Perl and the Web is important. Java and JavaScript get all the glamour, but any web monkey knows that Perl lurks at the back end of most servers. Many web-munging libraries in Perl are easily adapted to XML. The developers who have worked in Perl for years building web sites are now turning their nimble fingers to the XML realm.

Ultimately, you'll choose the programming language that best suits your needs. Perl is ideal for working with XML, but you shouldn't just take our word for it. Give it a try.



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