Rewrite any sub-domain and all files to a single directory - .htaccess

Question

When a user goes to any subdomain of my website, for example test.domain.com or even sdjfhdihdfig.domain.com, I want the page of http://www.domain.com/directory to be shown (this directory will be the same regardless of the subdomain the user goes to).
If the user heads over to any page of any subdomain (for example, test.domain.com/apage.html), I want the page of http://www.domain.com/directory/[PAGE] to be shown (in this case the page www.domain.com/directory/apage.html would be shown, but of course this would change depending on what came after the subdomain).
I found something that seems to solve this problem, however, it redirects the user rather than keeping the subdomain as it is in the URL bar. If I went to test.domain.com/test, I want this URL to stay as it is, but the page located at www.domain.com/directory/test should be served instead.
Does anyone have any ideas about how I could do this with htaccess? Thanks in advance.

Answer 1

Try adding this to the .htaccess file in your web document root folder (often public_html or htdocs):
Options +FollowSymLinks -MultiViews
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(?!www)[^.]+\.domain\.com [NC]
RewriteRule ^(.*)$ http://www.domain.com/directory/$1 [R,L]
Once you are satisfied that the redirect works, you can change the R to R=301 to make it permanent.
This assumes that mod_rewrite is both installed and activated for .htaccess files.
If you are not sure, to check if mod_rewrite is even installed, look at the list of installed modules in the output of phpinfo();
By default, mod_rewrite is not enabled for .htaccess files. If you are managing your own server, open httpd.conf
and make sure that the webroot directory block contains one of these lines: AllowOverride FileInfo or AllowOverride All

Answer 2

I managed to figure out the solution to my problem eventually.
This is my .htaccess document:
Options +FollowSymLinks
Options -MultiViews
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{HTTP_HOST} ^(?!www\.)?(.+)$
RewriteRule ^$ s/$1/ [L]
When someone goes to example.domain.com, the page at http://www.domain.com/s/ is displayed. When they go to a page like example.domain.com/s/page.html, the page at http://www.domain.com/s/page.html is displayed instead.
If the user goes to www.domain.com, this is not treated as a subdomain and instead my main website homepage is displayed.
I've set up a quick script so if someone decides to go to example.domain.com/page.html, instead of showing the page from www.domain.com/page.html, they are redirected to a 404 page on my server. The script (PHP) for how to do this is below:
if(substr($_SERVER['HTTP_HOST'], 0, 4) != 'www.' AND substr($_SERVER['REQUEST_URI'], 0, 3) != '/s/' AND $_SERVER['REQUEST_URI'] != '' AND $_SERVER['REQUEST_URI'] != '/') {
header("Location: http://www.domain.com/404.php");
}
I got the htaccess file from htaccess get domain name from %{HTTP_HOST} into variable, minus the www and just adapted it a little bit.
I hope this helps someone in the future!