mod_rewrite is redirecting instedad of rewriting - url

Question

I must be missing something obvious, but I can't make it work
I want to have nice urls with subdomains, but instead of some directories I want to read the subdomain's content from the file:
RewriteEngine On
RewriteBase /
Options +FollowSymlinks
RewriteCond %{HTTP_HOST} ^subdomain.example.com
RewriteRule (.*) http://example.com/subdomain.php
These rules works, but if I enter subdomain.example.com I am redirected to example.com/subdomain.php - but I do not want this, I just want internally rewrite the url...
Thank you very much! I tried [QSA, L], do not work.

Answer 1

If you replace this:
RewriteRule (.*) http://example.com/subdomain.php
With this, I suspect it will work as you are expecting:
RewriteRule (.*) subdomain.php
There is no need to rewrite the domain unless you actually want to redirect to another domain, you only need to rewrite the request to point to the appropriate file. Indeed as you discovered rewriting the domain will cause a redirect. Normally RewriteRule matches all of the request after the domain, so just the path and query.

Answer 2

Rather than use mod rewrite for this, if you have access to the DNS controls of your domain, you could set a catchall subdomain with a wildcard (either '%' or '*') that directs to the same local directory. There, you could have a PHP script which all requests are directed to using:
Options +FollowSymlinks
RewriteEngine on
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+)$ /index.php?p=$1 [L]
and this would run all the requests into that PHP file. There you can have something that checks the $_SERVER variables for the requested domain, and a checker to see the subdomain. There it could use something such as a file_get_contents() subroutine to forward the relevant data to the client, and have 404 or 403 header responses if a request is made that may be valid, but not to that subdomain.
hope that makes sense...