Simple PHP script to get the user IP and writes it to the file.

visitorsip.php

<?php
//get tht ip from the user
$ip=$_SERVER['REMOTE_ADDR'];
//open or create the file
$arquivo = fopen($filename, "a");
if ($arquivo == false) {
  die('Error message creating or opening the file.');}
//write to the file the IP from the user
if (!fwrite($arquivo, $ip."\n")) die('Error updating the file.');{
	echo 'Sucess.';
	fclose($arquivo);
}
?>