#!/usr/bin/perl

use strict;
use warnings;

use XML::LibXML;

my $xml = <<_XML;
<doc>
  <a>
    <b>
      <c d="foo"/>
    </b>
  </a>
</doc>
_XML


my $parser = XML::LibXML->new();
my $doc    = $parser->parse_string( $xml );
my $val    = $doc->findvalue( '/doc/a/b/c/@d' );

print $val, "\n";