.htaccess redirect - automatically add www. if no subdomain exists

I need any www. added automatically to my domain ONLY IF a subdomain is not already there. I do want subdomains to bypass this redirect.

How can I do this?

Solution 1:

To automatically add a www to your domain name when there isn't a subdomain, add this to the htaccess file in your document root:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^[^.]+\.[^.]+$
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [L,R=301]