Get current directory name in htaccess and prevent redirection

I have this .htaccess file:

Options +FollowSymLinks
DirectorySlash On
RewriteEngine On

# Remove trailing slash for non directories
RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule ^(.*)/$ /mydir%1/$1 [R,L=303]

# Make direct files accessible
RewriteCond %{REQUEST_FILENAME} !-f

RewriteCond […]

See original post by invalid@example.com (omidgfx)