perl - Extracting data from an XML document that uses namespaces

Question

I have some XML files where I want to use some information from them. I have written a code that reads those files and then looks for some conditions.

The problem is that these XML file begins with

   <SquishReport version="2.1" xmlns="http://www.froglogic.com/XML2">

and Perl could not read them (at least in my code!). But When I am appending these lines in the first line of XML file

   <?xml version="1.0" encoding="UTF-8"?>
   <?xml-stylesheet type="text/xsl"?>

works very well.

Some lines from my XML file test.xml:

<SquishReport version="2.1" xmlns="http://www.froglogic.com/XML2">
   <test name="TEST">
      <prolog time="2015-10-01T03:45:22+02:00"/>
      <test name="tst_start_app">
          <prolog time="2015-02-01T03:45:23+02:00"/>
          <message line="38" type="LOG" file="C:squishestsources.py" time="2015-02-01T03:45:23+02:00">
              <description>
                <![CDATA[>>  >>  >> start: init (global) - testcase C:squishestst_start_app]]></description>
          </message>
       </test>
   </test>
</SquishReport>

and the Perl code for reading the XML file is:

use strict;
use warnings;
use feature 'say';
use XML::LibXML;

# Parse the XML
my $xml = XML::LibXML->load_xml(location => 'test.xml');

# Iterate the entries
for my $entry ($xml->findnodes('/SquishReport/test/test')) {
    my $key = $entry->findvalue('@name');
    say "$key";
}

Answer 1

The root node of that document is an element which has name SquishReport in the http://www.froglogic.com/XML2 namespace. Concisely, we can say the root node is a

{http://www.froglogic.com/XML2}SquishReport

When one uses SquishReport (as opposed to prefix:SquishReport) in an XPath, that tries to match an element which has name SquishReport in the null namespace. Concisely, we can say it attempts to match a

{}SquishReport

To specify the namespace, one uses prefixes defined in a context, as follows:

use strict;
use warnings;
use feature qw( say );

use XML::LibXML               qw( );
use XML::LibXML::XPathContext qw( );

my $xpc = XML::LibXML::XPathContext->new();
$xpc->registerNs(sr => 'http://www.froglogic.com/XML2');

my $doc = XML::LibXML->load_xml( location => 'test.xml' );
for my $entry ($xpc->findnodes('/sr:SquishReport/sr:test/sr:test', $doc)) {
    my $key = $entry->findvalue('@name');
    say $key;
}

Note: The prefix used in the XPath have no relation to the prefixes used in the XML document (if any). You are expected to know the namespace in which resides the elements for which you are searching, but not the prefixes used by a given document.