Subdomain redirection to folder without changing URL

Question

I have a primary domain which is pointed to primary folder like below

http://www.primary.com -> /var/www/html/primary

I need to make the below working without changing the URL to http://www.primary.com/sub

http://sub.primary.com -> /var/www/html/sub

Answer 1

RewriteEngine on
RewriteCond %{HTTP_HOST} ^(.*)\.primary\.com$ [NC]
RewriteRule !^(.*)\.primary\.com /%1%{REQUEST_URI}  [NC,NE,L]