Generic .htaccess www.redirect

Question

There are plenty of examples here of how to redirect example.com to www.example.com, but I'm looking for a generic version, so the same htacess code would also work to redirect example.net to www.example.net and example.org to www.example.org. I'm sure this exists (indeed, I have a vague memory I've done it before, somewhere), but I'm fairly unfamiliar with htaccess regex.

I need a way to match the condition HTTP_HOST does not begin with www..

Answer 1

#Enable RewriteEngine
RewriteEngine On

# For a way to check HTTP_HOST not beginning with www:    
RewriteCond %{HTTP_HOST} !^www [nc]

# As ! don't set backreferences we use this to match the hostname we need
RewriteCond %{HTTP_HOST} ^(.*)$ [nc]

# For the Redirect itself:
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]

Answer 2

Look at this question on stackoverflow.

http://stackoverflow.com/questions/234723/generic-htaccess-redirect-www-to-non-www