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

Question

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

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]

Comments

[kdjernigan]

Thank you. This seems to work. Can you explain why the previous one didn't work in your opinion? I noticed it working; however, then noticed that my subdomain didnt work. Not sure if this was related or not or just propagation issues. I would love to learn more about what each line means of the 2 answers. Thanks!

[Jon Lin]

@kdjernigan the www was never added to the redirect, and the first condition matches a subdomain.

[Kevin Beal]

This doesn't appear to work unless it's at the top of my .htaccess file... which is fine. Just strange.

[jezmck]

Does this solution assume a TLD with only one dot? i.e. it won't work for .co.uk?

[umefarooq]

its checking only one dot in TLD to make it work with .co.uk you need to check two dots here is my quick solution RewriteCond %{HTTP_HOST} ^[^.]+\.[^.]+\.[^.]+$ just change this condition rest remain same

[LWC]

TLD assumption aside, how does it know the difference between www and a subdomain? Don't they look the same to the regex?

[Jon Lin]

@LWC the regex is only checking the domain and TLD, it won't know the difference between a "www" or any other subdomain. Thus if there is a subdomain, or a "www", the condition fails and the rule is skipped.

[Admin]

does not work on apache 2.4 - it results in: www.sub.domain.com