google.php

<?php
$q = $_GET['q'];

$googStump = "https://www.google.com/search?q=";
$gooogle = $googStump.rawurlencode($q);

// custom keys
$keys = [
    'hn' => 'https://news.ycombinator.com/',
];

if (isset($keys[$q])) {
    $url = $keys[$q];
    // custom key
}elseif (substr($q, 0, 2)==='g ') {
    // force google (in case you're googling for something which is also a custom key)
    $url = $googStump.rawurlencode(substr($q, 2));
}else{
    // default to google
    $url = $gooogle;
}

header("Location: $url");