htaccess: redirigir un subdominio a una carpeta concreta

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(.*)\.midominio.com
RewriteRule ^(.*)$ http://midominio.com/$1 [L,NC,QSA]

RewriteEngine on
RewriteCond %{HTTP_HOST} !^www\.midominio\.com
RewriteCond %{HTTP_HOST} ^(.*)\.midominio\.com
RewriteCond %{REQUEST_URI} !^/([a-zA-Z0-9-z\-]+)
RewriteRule ^(.*)$ /%1/$1 [L]