This Apache Config takes the subdomain part of a url if available (except www) and tries to find files in the document root with subdomain appended if the file cannot be found their i tries a second directory, in thies case the top level doc root

subdomain_rewrite

RewriteEngine on
RewriteLogLevel 2
RewriteLog /var/www/sites/camino_surf/logs/rewrite.log

RewriteCond %{HTTP_HOST} !www.caminosurf.com$ [NC]
RewriteCond %{HTTP_HOST} ^(www.)?([a-z0-9-]+).caminosurf.com [NC]

#   first try to find it in branch dir based on subdomain
#   ...and if found stop and be happy:
RewriteCond         /var/www/sites/camino_surf/public/%{REQUEST_FILENAME}  -f
RewriteRule  ^(.+)  /var/www/sites/camino_surf/public/%2/$1 [L]

#   second try to find it in toplevel public content
#   ...and if found stop and be happy:
RewriteCond         /var/www/sites/camino_surf/public/%{REQUEST_FILENAME}  -f
RewriteRule  ^(.+)  /var/www/sites/camino_surf/public/$1  [L]

#   else go on for other Alias or ScriptAlias directives,
#   etc.
RewriteRule   ^(.+)  -  [PT]