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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.

TABLE OF CONTENTS:
  1. Using Perl with XML (part 1)
  2. Getting Down To Business
  3. Let's Talk About SAX
  4. Breaking It Down
  5. Call Me Back
  6. Random Walk
  7. What's For Dinner?
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 20
January 15, 2002

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In addition to elements and CDATA, Perl also allows you to set up handlers for other types of XML structures, most notably PIs, entities and notations (if you don't know what these are, you might want to skip this section and jump straight into another, more complex example on the next page). As demonstrated in the previous example, handlers for these structures are set up by specifying appropriate callback functions via a call to the setHandlers() object method.

Here's a quick list of the types of events that the parser can handle, together with a list of their key names (as expected by the setHandlers() method) and a list of the arguments that the corresponding callback function will receive.

Key Arguments Event to callback ------------------------------------------------------------------------ Final parser handle Document parsing completed Start parser handle, Start tag found element name, attributes End parser handle, End tag found element name Char parser handle, CDATA found CDATA Proc parser handle, PI found PI target, PI data Comment parser handle, Comment found comment Unparsed parser handle, entity, Unparsed entity found base, system ID, public ID, notation Notation parser handle, notation, Notation found base, system ID, public ID XMLDecl parser handle, XML declaration found version, encoding, standalone ExternEnt parser handle, base, External entity found system ID, public ID Default parser handle, data Default handler
As an example, consider the following example, which uses a simple XML document,

<?xml version="1.0"?> <random> <?perl print rand(); ?> </random>
in combination with this Perl script to demonstrate how to handle processing instructions (PIs):

#!/usr/bin/perl # include package use XML::Parser; # initialize parser $xp = new XML::Parser(); # set PI handler $xp->setHandlers(Proc => \&pih); # output some HTML print "Content-Type: text/html\n\n"; print "<html><head></head><body>And the winning number is: "; $xp->parsefile("pi.xml"); print "</body></html>"; # this is called whenever a PI is encountered sub pih() { # extract data my ($parser, $target, $data) = @_; # if Perl command if (lc($target) == "perl") { # execute it eval($data); } } # end
In this case, the setHandlers() method knows that it has to call the subroutine pih() when it encounters a processing instruction in the XML data; this user-defined pih() function is automatically passed the PI target and the actual command to be executed. Assuming the command is a Perl command - as indicated by the target name - the function passes it on to eval() for execution.

 
 
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