#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use XML::LibXML;

my $dom = 'XML::LibXML'->load_xml(location => shift);
my $xpc = 'XML::LibXML::XPathContext'->new($dom);
my $rpt = 1;
$xpc->registerNs("ns$rpt", 'http://www.url.com/path/for/rpt');

my $nsdevices = "//ns$rpt:device";
my @devices = $xpc->findnodes($nsdevices);
say $_->getAttribute('timestamp') for @devices;