A short one in the original spirit of this notepad, ie “I really don’t want to lose this ever again” :
header("HTTP/1.1 301 Moved Permanently");
For some reason I’ve always had a hard time setting this kind of headers in PHP. Now that I have the solution it just seems so trivial… 301 (permanent) redirects are an important thing to have when you’re changing the structure of your site’s URLs, this way search engines should be able to transfer your former URLs to your new ones. If you just do a 302 (temporary) redirect, they (most likely) won’t, or at least you might lose more pagerank than you should.
And here’s a more complete script if you want to redirect all your URLs to rewritten URLs instead of just a single same page:
$host = $_SERVER['HTTP_HOST'];
$uri = $_SERVER["REQUEST_URI"];
header('HTTP/1.1 301 Moved Permanently');
Source (contains examples in other programming languages, notably in Perl and using only mod_rewrite): http://www.somacon.com/p145.php