[root@dw01 xml]# ls
last.xml  test.pl
[root@dw01 xml]# more last.xml
<?xml version="1.0" encoding="iso-8859-1" ?>
<?meta name="GENERATOR" content="XML::Smart/1.6.9 Perl/5.008008 [linux]" ?>
<global_status>
  <status name="Uptime" value="4630" value_var="-861958"/>
</global_status>
[root@dw01 xml]# more test.pl
#! /usr/bin/perl
use XML::Smart;
#get last status
my $xml_last_status = XML::Smart->new('last.xml');
my $last_status_data = $xml_last_status->{global_status}->{status}[0];
my $last_value = $last_status_data->{value};
my $now_value = 5360;
my $value_var = $now_value - $last_value;
print "last_value: $last_value, now_value: $now_value, value_var: $value_var\n";
[root@dw01 xml]# ./test.pl
last_value: 4630, now_value: 5360, value_var: -730
[root@dw01 xml]#