#!/usr/bin/perl

use strict;
use warnings;
use LWP;
use Data::Dumper;

my $browser = LWP::UserAgent->new();
my $site = $browser->get('http://de.wikibooks.org');
my $code = $site->decoded_content();

use XML::LibXML;
my $dom = XML::LibXML->load_xml(string => $code);
foreach my $node ($dom->findnodes('//link[@rel="canonical"]/@href')) {
    print $node->to_literal(), " # canonical LibXML\n";
}

use XML::XPath;
my $xp = XML::XPath->new(xml => $code);
foreach my $node ($xp->findnodes('//link[@rel="canonical"]')) {
    print $node->getAttribute('href'), " # canonical XPath\n";
}