URL shortener

.htaccess

RewriteEngine On
RewriteRule ^(\w{5})$ /index.php?key=$1

index.php

<?php

header('Content-Type: text/plain');

// Add url
if (isset($_GET['add'])) {
    $db = dba_open("/tmp/shortener.db", "c", "db4");
    if (!$db) trigger_error("dba_open failed", E_USER_ERROR);

    $key = substr(base_convert(md5($_GET['add']), 10, 36), 0, 5);
    dba_insert($key, $_GET['add'], $db);
    dba_close($db);

    echo "http://{$_SERVER['HTTP_HOST']}/$key";
    exit();
}

// Get url
$db = dba_open("/tmp/shortener.db", "r", "db4");
if (!$db) trigger_error("dba_open failed", E_USER_ERROR);

if (isset($_GET['key']) && dba_exists($_GET['key'], $db)) {
    $url = dba_fetch($_GET['key'], $db);
}
dba_close($db);

if (!isset($url)) {
    header("HTTP/1.0 404 Not Found");
    echo "Not found $_GET[key]";
    exit();
}

header("Location: $url");
echo $url;