.htaccess - alias domain root to subfolder - .htaccess

Question

I've got an install of concrete5 living in my site root - the problem is that the C5 file structure is pretty varied, and it's getting mixed in with my subdirs and subdomains. I can't tell what's my code and what's C5, I hate it.
My solution is to move everything to a /_concrete/ folder - but since my domain has to point to the root, I can't use the files here.
Enter .htaccess: I need to write a script to redirect any instance of www.domain.com (ignore subdomains) to www.domain.com/_concrete/ - but not a transparent 301, just an alias. To clarify: www.domain.com/page/ and www.domain.com/_concrete/page/ should display the same thing. www.domain.com/page/ should NOT change it's URL to www.domain.com/_concrete/page/.
I've adapted this from a similar script I use elsewhere:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ /_concrete/$1 [L,QSA]
But this only causes a server error. I hope I'm close - can anyone point me in the right direction?

Answer 1

You're telling the server to check if the value is not a filename, but you're not having it ignore the _concrete directory itself (which would also match your script and create a loop).
This might get you closer to what you're trying to do.
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !^_concrete
RewriteRule ^(.*)$ _concrete/$1 [L,QSA]
Additionally you might want to have it ignore directories that exist as well. At which point _concrete would no longer be matched because it exists.
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ _concrete/$1 [L,QSA]