<?php

  $file = 'dynip.txt';
  $current_ip = $_SERVER['REMOTE_ADDR'] ."\n";
  $saved_ip = file_get_contents($file);

  if (isset($_GET["update"])) {
    if ($current_ip != $saved_ip) {
      file_put_contents($file, $current_ip);
    }
  } else {
    echo $saved_ip;
  }

?>