You can use XML::LibXML::XPathContext to register the namespace as follows: 
use strict;
use warnings;

use XML::LibXML;
use XML::LibXML::XPathContext;

# load the XML doc
my $p = XML::LibXML->new;
my $xml_file = do { local $/; <DATA> };
my $dom = $p->parse_string( $xml_file );

# register the namespace
my $xc = XML::LibXML::XPathContext->new( $dom );
$xc->registerNs('ns', 'http://www.w3.org/2005/Atom');

# select using XPath
my @nodes = $xc->findnodes( '/ns:feed/ns:entry');
print $_->toString for @nodes;

__DATA__
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:os="http://a9.com/-/sp
+ec/opensearch/1.1/">
<os:totalResults>233</os:totalResults>
<os:startIndex>1</os:startIndex>
<os:itemsPerPage>233</os:itemsPerPage>
<os:Query role="request" searchTerms="test" startPage=""/>
        <entry>
                <id>34</id>
                <channel>1</channel>

                <title>Decision making: Marmite</title>               
+ <description>A meeting of the 'business group', which is the committ
+ee set up to steer the development of the new Squeezy Marmite bottle.
+ They discuss the qualities of the new bottle and agree to test i
t with consumers.</description>
                <author></author>
                <size>36145156</size>
                <date>2007-09-07</date>
                <uri>assets/asset10000/aaiiaaaaaaafnknn.mpg</uri>

                <keylearningstage></keylearningstage>
                <keywords></keywords>
                <source>C4L Secondary Service</source>
        </entry>
</feed>

[download]

In reply to Re^2: XML::LibXML's findnodes is beahving weirdly by un-chomp
in thread XML::LibXML's findnodes is beahving weirdly by nabeel

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