#!C:/Perl

use XML::Parser;
use XML::Parser::Expat;
use XML::Twig;

my $t = XML::Twig->new( 
   twig_roots => { 
   '/invoice/header/accountnumber' => \&print_elt_text 
   } );
   
$t->parsefile('MyHugeXML.xml');

sub print_elt_text { 
     my( $t, $elt ) = @_;
     print $elt->text;
     $t->purge;
   }