#!/usr/bin/perl

use strict;
use warnings;
use XML::Twig;
use Data::Dumper;


my $xml =  qq|<?xml version="1.0" encoding="ISO-8859-1"?>
<CustDetails>
<CustName>Unix</CustName>
<CustomerId>999</CustomerId>
<Age>28</Age>
</CustDetails>
|;

my $t= XML::Twig->new( twig_handlers => 
                           { 'CustDetails/CustomerId' => sub { $_->print } }
                       )
                  ->parsefile($xml);
warn Dumper $t;