Regex parse subdomain and redirect - regex

Question

I have been trying to figure this out for nearly 2 hours now and can't get it working so I hope some of you can help me out. Please note I pretty new to PHP and regex.
Ok so I am trying to setup a redirect that will redirect to certain pages based on text in the subdomain. I have wildcards setup for my subdomains and any subdomain URL now redirects to this php file containing the code below.
So if someone comes to anytexthere.domain.com they arrive at domain.com/redirect.php
This php file will be used to send them to the correct relevant URL.
To do this I am going to use subdomains such as anythinghere-1.domain.com and then have my code check what appears in the subdomain after - and before the .domain. If it equals in this case 1 go to whatever URL matches it and so on.
Code so far:
<?php
$host = $_SERVER['SERVER_NAME'];
preg_replace('(?<=-).*?(?=\.)', $host, $matches);
$url = $matches;
switch ($url)
{
case "1":
header("Location: http://www.website.com/page-here/");
break;
case "test":
header("Location: http://www.website.com/this-is-a-test/");
break;
case "another":
header("Location: http://www.website.com/another-page-here/");
break;
default:
header("Location: http://www.website.com");
break;
}
?>
As you can see I have cases there that use text e.g "another" instead of numbers because I will need it to work if I choose to use text or numbers after the - in the subdomain.
This code as it is now is giving me the following errors:
Warning: preg_replace() [function.preg-replace]: Unknown modifier '.' in thelocationhere on line 4
and
Warning: Cannot modify header information - headers already sent by (output started at thelocationhere:4) in thelocationagain on line 22
I believe the second error above has something to do with the default case.
I really appreciate any help with this. I have spent a lot of time searching all over for snippets of code and testing them but I haven't got it to work on my own.
Thanks,
Peter

Answer 1

You have a small mistake - you used preg_replace instead of preg_match. also, you need to pad your regular expression with /. so it should be:
preg_match('/(?<=-).*?(?=\.)/', $host, $matches);
By the way, you didn't mention how you are making everyone who try and access *.domain.com to reach domain.com/redirect.php., but I'm assuming you are using htaccess and the RewriteEngine. You could just directly type it in the RewriteRule.
The "Headers already sent" means some output was sent to the browser. Did you save your file as UTF-8 without BOM? or maybe you've printed something to the browser prior to the redirect?
There could also be some stray spaces at the beginning of the file....