Redirect with HTTP_HOST redirects to sub subdomain

Question

The settings

I have the following .htaccess rule

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

This works great to redirect any subdomain that is not valid (www or de) to the www subdomain.

I have seen solution, but they only depend on single domain sites.

I have multiple domains:

http://www.example.com
http://www.example.net
http://de.example.com

which all serve their own brand of site.

Now I have the .htaccess rule that is mentioned above and it works beautifully if someone types in http://example.com it redirects to http://www.example.com.

The problem

If someone types in http://test.example.com, it redirects to http://www.test.example.com and if someone types in http://test.example.net, it redirects to http://www.test.example.net.

The question

How can I make it so that it redirects http://test.example.com to http://www.example.com? And http://test.example.net to http://www.example.net.

I need an domain insensitve solution because more domains will be added in the future.

Solution

To redirect using the sub-domain as a parameter:

# HTTP 301 Redirect test.*.net -> www.*.net
RewriteCond %{HTTP_HOST} ^test.([^.]+).net$ [NC]
RewriteRule (.*) http://www.%1.net/$1 [R=301,L)

# HTTP 301 Redirect test.*.com -> www.*.com
RewriteCond %{HTTP_HOST} ^test.([^.]+).com$ [NC]
RewriteRule (.*) http://www.%1.com/$1 [R=301,L)

If you also want to redirect when there's no subdomain (e.g. http://example.com) to the main website using the www. subdomain (http://www.example.com):

# HTTP 301 Redirect *.net -> www.*.net
RewriteCond %{HTTP_HOST} ^([^.]+).net$ [NC]
RewriteRule (.*) http://www.%1.net/$1 [R=301,L)

# HTTP 301 Redirect *.net -> www.*.net
RewriteCond %{HTTP_HOST} ^([^.]+).com$ [NC]
RewriteRule (.*) http://www.%1.com/$1 [R=301,L)

If you're trying to achieve a lot with your .htaccess files you may find it helps to test your conditions and how they affect URL rewriting on the htaccess Made-With-Love website.

In case this is where you struggled, it is always worth remembering that in .htaccess, parameters prefixed with percent symbols (e.g. %1) reference values from the last matched RewriteCond expression, normally values that have been marked as being of interest by being surrounded in brackets (), and parameters prefixed with dollar symbols (e.g. $1) reference values in the RewriteRule expression, normally values that are automatically assigned by Apache and relating to the URL.