htaccess redirect from several subdomains by removing the dot

Question

I have a set of sub-subdomains that I need to redirect in .htaccess. I'm not good at REGEX, and have failed to understand other posts I've read well enough to apply it to this situation.

My sites are laid out like this:

quark.subdomain.site.com
yy.subdomain.site.com
bit.subdomain.site.com
etc

Where the sub-subdomain can be anything, but the subdomain is always the same.

I need to redirect them to:

quarksubdomain.site.com
yysubdomain.site.com
bitsubdomain.site.com
etc

So basically, I just need to remove the dot.

I was able to get this far, using the answer from this question: .htaccess 301 redirect one subdomain to another, for multiple TLDs

But this is doing each sub-subdomain individually:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^quark.subdomain\.(.+)$ [NC]
RewriteRule ^ https://quarksubdomain.%1 [L,R=301]

RewriteCond %{HTTP_HOST} ^yy.subdomain\.(.+)$ [NC]
RewriteRule ^ https://yysubdomain.%1 [L,R=301]

But I have 30 or so of these sub-subdomains, so I'd like something more efficient.

1) Is there a wildcard method I can use to just remove the dot from any sub-subdomain of subdomain?

2) I am failing to pass any part of the address that comes after the domain.com/ . I am using CakePHP, so REQUEST_URI does not work, because it gives me address information that Cake hides. What is the best way to do this without using REQUEST_URI?

Bonus points for a link that explains the REGEX special characters for beginners. I would like to correct my ignorance.

Answer 1

You don't need to get the Request URI from the condition, you can get if from the rewrite rule, and optimise what you keep from the cond:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^(.+)\.subdomain\.site\.com$ [NC]
RewriteRule (.+) https://%1subdomain.site.com$1 [L,R=301]

Bonus point... I don't know, https://regexone.com/ maybe?

Answer 2

After some trial and error, I was finally successful with the following:

RewriteCond %{HTTP_HOST} ^(.+)\.subdomain\.(.*)$ [NC]
RewriteRule ^(.*)$ https://%subdomain.%2/$1 [QSA,L,R=301]

It correctly gets any prefix and appends it to the subdomain name, and also passes the locations following the .com/ correctly. I also made it domain insensitive, so it works natively on my development domain also.

I can't give myself any bonus points though, because I still can't explain why it has to be exactly this way to pass the specific page address.