#!/usr/bin/perl

use strict;
use warnings;
use XML::Twig;

 my $twig= XML::Twig->new(
                             TwigHandlers => {
                                "eSearchResult/IdList/Id" => \&id_Tag
                                             }
                         );

   $twig->parsefile("bla.xml") or die "cannot parse : $!";

sub id_Tag {
    my($t, $idTag)= @_;
    print $idTag->text(), "\n";
    # Release memory of processed tree up to here
    $t->purge();
}