참조: O'Reilly Apache Cookbook Jan. 2008 pdf

Rewriting a Hostname to a Directory

You want requests for

http://bogus.example.com/

to be turned into requests for

http://example.com/bogus/

To do this transparently, without a redirect:

RewriteEngine On
RewriteCond "%{HTTP_HOST}" "^([^.]+)\.example\.com$"
RewriteRule "(.*)" "/%1$1" [PT]

Apache2 module enable:
$ sudo a2enmod rewrite