Free PHP URL shortener script that kicks ass

$shortenedurl = file_get_contents('http://yourdomain.com/shorten.php?longurl=' . urlencode('http://' . $_SERVER['HTTP_HOST']  . '/' . $_SERVER['REQUEST_URI']));

<?php
/*
 * First authored by Brian Cray
 * License: http://creativecommons.org/licenses/by/3.0/
 * Contact the author at http://briancray.com/
 */

ini_set('display_errors', 0);

$url_to_shorten = get_magic_quotes_gpc() ? stripslashes(trim($_REQUEST['longurl'])) : trim($_REQUEST['longurl']);

if(!empty($url_to_shorten) && preg_match('|^https?://|', $url_to_shorten))
{
    require('config.php');

    // check if the client IP is allowed to shorten
    if($_SERVER['REMOTE_ADDR'] != LIMIT_TO_IP)
    {
        die('You are not allowed to shorten URLs with this service.');
    }
    
    // check if the URL is valid
    if(CHECK_URL)
    {
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url_to_shorten);
        curl_setopt($ch,  CURLOPT_RETURNTRANSFER, TRUE);
        $response = curl_exec($ch);
        curl_close($handle);
        if(curl_getinfo($ch, CURLINFO_HTTP_CODE) == '404')
        {
            die('Not a valid URL');
        }
    }
    
    // check if the URL has already been shortened
    $already_shortened = mysql_result(mysql_query('SELECT id FROM ' . DB_TABLE. ' WHERE long_url="' . mysql_real_escape_string($url_to_shorten) . '"'), 0, 0);
    if(!empty($already_shortened))
    {
        // URL has already been shortened
        $shortened_url = getShortenedURLFromID($already_shortened);
    }
    else
    {
        // URL not in database, insert
        mysql_query('LOCK TABLES ' . DB_TABLE . ' WRITE;');
        mysql_query('INSERT INTO ' . DB_TABLE . ' (long_url, created, creator) VALUES ("' . mysql_real_escape_string($url_to_shorten) . '", "' . time() . '", "' . mysql_real_escape_string($_SERVER['REMOTE_ADDR']) . '")');
        $shortened_url = getShortenedURLFromID(mysql_insert_id());
        mysql_query('UNLOCK TABLES');
    }
    echo BASE_HREF . $shortened_url;
}

function getShortenedURLFromID ($integer, $base = ALLOWED_CHARS)
{
    $length = strlen($base);
    while($integer > $length - 1)
    {
        $out = $base[fmod($integer, $length)] . $out;
        $integer = floor( $integer / $length );
    }
    return $base[$integer] . $out;
}

<?php
/*
 * First authored by Brian Cray
 * License: http://creativecommons.org/licenses/by/3.0/
 * Contact the author at http://briancray.com/
 */

ini_set('display_errors', 0);

if(!preg_match('|^[0-9a-zA-Z]{1,6}$|', $_GET['url']))
{
    die('That is not a valid short url');
}

require('config.php');

$shortened_id = getIDFromShortenedURL($_GET['url']);

if(CACHE)
{
    $long_url = file_get_contents(CACHE_DIR . $shortened_id);
    if(empty($long_url) || !preg_match('|^https?://|', $long_url))
    {
        $long_url = mysql_result(mysql_query('SELECT long_url FROM ' . DB_TABLE . ' WHERE id="' . mysql_real_escape_string($shortened_id) . '"'), 0, 0);
        @mkdir(CACHE_DIR, 0777);
        $handle = fopen(CACHE_DIR . $shortened_id, 'w+');
        fwrite($handle, $long_url);
        fclose($handle);
    }
}
else
{
    $long_url = mysql_result(mysql_query('SELECT long_url FROM ' . DB_TABLE . ' WHERE id="' . mysql_real_escape_string($shortened_id) . '"'), 0, 0);
}

if(TRACK)
{
    mysql_query('UPDATE ' . DB_TABLE . ' SET referrals=referrals+1 WHERE id="' . mysql_real_escape_string($shortened_id) . '"');
}

header('HTTP/1.1 301 Moved Permanently');
header('Location: ' .  $long_url);
exit;

function getIDFromShortenedURL ($string, $base = ALLOWED_CHARS)
{
    $length = strlen($base);
    $size = strlen($string) - 1;
    $string = str_split($string);
    $out = strpos($base, array_pop($string));
    foreach($string as $i => $char)
    {
        $out += strpos($base, $char) * pow($length, $size - $i);
    }
    return $out;
}

<?php
/*
 * First authored by Brian Cray
 * License: http://creativecommons.org/licenses/by/3.0/
 * Contact the author at http://briancray.com/
 */

// db options
define('DB_NAME', 'your db name');
define('DB_USER', 'your db usernae');
define('DB_PASSWORD', 'your db password');
define('DB_HOST', 'localhost');
define('DB_TABLE', 'shortenedurls');

// connect to database
mysql_connect(DB_HOST, DB_USER, DB_PASSWORD);
mysql_select_db(DB_NAME);

// base location of script (include trailing slash)
define('BASE_HREF', 'http://' . $_SERVER['HTTP_HOST'] . '/');

// change to limit short url creation to a single IP
define('LIMIT_TO_IP', $_SERVER['REMOTE_ADDR']);

// change to TRUE to start tracking referrals
define('TRACK', FALSE);

// check if URL exists first
define('CHECK_URL', FALSE);

// change the shortened URL allowed characters
define('ALLOWED_CHARS', '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');

// do you want to cache?
define('CACHE', TRUE);

// if so, where will the cache files be stored? (include trailing slash)
define('CACHE_DIR', dirname(__FILE__) . '/cache/');

DirectoryIndex index.php

# remove the next 3 lines if you see a 500 server error
php_flag register_globals off
php_flag magic_quotes_gpc off
php_value display_errors 0

FileETag none
ServerSignature Off

Options All -Indexes

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^shorten/(.*)$ shorten.php?longurl=$1 [L]
RewriteRule ^([0-9a-zA-Z]{1,6})$ redirect.php?url=$1 [L]
</IfModule>