Rewrite wildcard subdomain and wildcard domain

Question

For a webserver where a bunch of domain names are hosted, we'd like te implement a redirect where any subdomain on any domain is redirect to its www. equivalent.

sub1.domain1.com -> www.domain1.com
sub2.domain5.com -> www.domain5.com
anothersub.moredomains.com -> www.moredomains.com
etc

I haven't been able to find a rewrite rule covering both wildcard subdomain and domain.

Any help is greatly appreciated!

Answer 1

If the domains always have two components (x.tld) then it's pretty easy. If you have to take into account things like x.co.uk then you'll need either a bigger rule or an actual list of the domains.

Not tested, but something like this might work.

# enable mod_rewrite
RewriteEngine On
# if the host is prefixed with www, don't match.
RewriteCond %{HTTP_HOST} !^www\.    
# match the last two components of the hostname (see below for a bette regex)
RewriteCond %{HTTP_HOST} (.+?)\.(.+?)$
# rewrite to the hostname from the match above (%1 and %2) plus the current url ($1).
RewriteRule /(.*) http://www.%1.%2/$1 [L,R=301]

Add

LogLevel alert rewrite:trace

and you can grep for 'rewrite:' in your error log for debugging information.

The (.+?) conditions might be more accurate as "anything but a dot" ([^\.]+), but I don't remember the exact syntax in whatever regex engine Apache uses, so the above version is simpler for you to have something working.