use XML::Parser;

$parser = new XML::Parser(Handlers => {Start => \&start_handler, Char  => \&char_handler});
          
$parser->parsefile("yourXML.xml");
  
$customer = 0;
$data_ok = 0;

sub start_handler
{
    $data_ok = 0;

    if ($_[1] eq "tagName"){
        $customer++;
    }

    if ($customer == 2){
        if($_[1] eq "tagName2"){
            $data_ok++;
        }
    }
}

sub char_handler
{
    if(($_[1] =~ /[^ \n\t\r]/g) && $data_ok){
        print "First name: $_[1]\n";
    }
}