RewriteCond backrefrence to another RewriteCond causing 500 - apache

Question

I have setup a *.mydomain.com subdomain in cpanel (cpanel, no shell access)
Going to anything.mydomain.com gets me to the same directory which I mounted for *.mydomain.com
So when I go to test.mydomain.com with the following in .htaccess,
What works properly is:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^(.+)\.(.+?\..+?)$ [NC]
RewriteCond %{REQUEST_URI} !^/test/(.+)?$
RewriteRule ^(.*) /%1/$1
What doesn't work and gives a 500 Error is this (Just replaced the test with %1):
RewriteEngine on
RewriteCond %{HTTP_HOST} ^(.+)\.(.+?\..+?)$ [NC]
RewriteCond %{REQUEST_URI} !^/%1/(.+)?$
RewriteRule ^(.*) /%1/$1
What I want to do is allow dynamic setup of subdomains if a subdirectory with it's name exists. The rewriting is done gracefully when I hardcode the subdomain name test in the .htaccess and not when I use a backrefrence %1 for it.

Answer 1

You can't use a % variable or a backreference as part of the regular expression in a RewriteCond. You can create a string usimg a backreference and a # regex backreference:
RewriteCond %1:%{REQUEST_URI} !^([^:]+):/\1/(.+)?$
So you create a string made up of the subdomain of the host match, a colon, then the URI, match against the subdomain in your regex, and reference it using \1.
Additionally, you may need to add another %{HTTP_HOST} match right after because the %1 backreference might have gotten reset because you can't backreference a non match.