htaccess rewrite / remove parent dir - .htaccess

Question

there's been similar posts about this but I can't quite seem to find what I need.
I want my .htacess to rewrite "up one level".
The Url would be somethign like
http://www.site.com/variable_dir/
or
http://www.site.com/variable_dir/sub_dir
I need that to basically rewrite the request to
http://www.site.com/
or
http://www.site.com/sub_dir
I DO want the URL to still show the original
http://www.site.com/variable_dir/
or
http://www.site.com/variable_dir/sub_dir
I currently have
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php [L]
This redirects to where I want, but this changes the URL to
http://www.site.com/
or
http://www.site.com/sub_dir
which I don't want.
I know it's simple but I just can't seem to get there.

Answer 1

The rule below woule rewrite http://www.site.com/variable_dir/ to http://www.site.com/ and http://www.site.com/variable_dir/sub_dir to http://www.site.com/sub_dir
RewriteEngine on
RewriteBase /
#for a request to /variable_dir
RewriteCond %{REQUEST_URI} ^/variable_dir/(.+)$
#rewrite it to directory without variable_dir
RewriteRule . /%1 [L]
Edit:
If the directory is not literally variable_dir, the rule above will not work. However, if you have a short list of directories, you could enumerate them as below.
RewriteEngine on
RewriteBase /
#only apply if this directory does not exist
RewriteCond %{REQUEST_FILENAME} !-d
#for any direcory enumerated here
RewriteCond %{REQUEST_URI} ^/(variable_dir|dir2|dir3|etc)/(.+)$
#rewrite it to directory without variable_dir
RewriteRule . /%2 [L]
If not, then ideally the directories would all have something in common so you could limit what the rule affects. If you want a completely variable dir, nothing in common, I don't recommend it, but you can try
RewriteEngine on
RewriteBase /
#only apply if this directory does not exist
RewriteCond %{REQUEST_FILENAME} !-d
#skip any top level directory
RewriteCond %{REQUEST_URI} ^/[^/]+/(.+)$
#rewrite it to directory without variable_dir
RewriteRule . /%1 [L]
Edit:
Finally if the trailing slash is optional, as in the example in your comment, change the RewriteCond and rule above to be
#skip any top level directory, optional trailing slash
RewriteCond %{REQUEST_URI} ^/[^/]+(/(.+))?$
#rewrite it to directory without variable_dir
RewriteRule . /%2 [L]