Get clients IP address in PHP

clientIPAddress.php

<?php
/**
 * Retuns client's IP address
 * @return string
 * @since 6/16/11 12:11 PM
 */
function getClientIPAddress() {
    if (getenv("HTTP_CLIENT_IP")) {
        $ip = getenv("HTTP_CLIENT_IP");
    } else {
        if (getenv("HTTP_X_FORWARDED_FOR")) {
            $ip = getenv("HTTP_X_FORWARDED_FOR");
        } else {
            if (getenv("REMOTE_ADDR")) {
                $ip = getenv("REMOTE_ADDR");
            } else {
                $ip = "UNKNOWN";
            }
        }
    }

    return $ip;
}