How mod_rewrite can add subdomain?

Question

RewriteEngine On
RewriteRule ^/ai?$ /Market/publish.jsp [QSA,L,PT]
RewriteRule ^/ar?$ /Market/MailDispatch [QSA,L,PT]
RewriteCond %{HTTP_HOST}   !^web\.example\.com [NC]
RewriteCond %{HTTP_HOST}   !^$
RewriteRule ^/(.*)         http://web.example.com/$1 [L,R]
#How skip www\. to web\. for this 1 ? 
#RewriteRule ^/vi/?([0-9]+)\.htm$ /Market/vi.do?id=$1 [PT,L]                    
RewriteRule ^/li /Market/list.do [QSA,PT,L]
RewriteRule ^/vi/locations.jsp /Market/locations.jsp [PT,L]
ErrorDocument 404 /notfound.html

Nearly undoable(?) I try http://example.com/vi/{N}.htm should redirect to http://web.example.com/vi/{N}.htm where N is dynamic ID.

Seen http://stackoverflow.com/questions/2229385/mod-rewrite-with-subdomain-and-url-pattern There is no clear way to make eg http://example.com/vi/1096.htm pass up to next version http://web.example.com/vi/1096.htm where number is dynamic. I tried

Answer 1

A rule with the following scheme should do it:

RewriteCond %{HTTP_HOST} ^example\.com$
RewriteRule ^/vi/\d+\.htm$ http://web.example.com%{REQUEST_URI} [L,R=301]

It’s important to put this rule in front of those rules that do an internal redirect. Otherwise an already internally rewritten URL could be rewritten externally.

If you want to use this rule in a .htaccess file, remove the leading slash from the pattern in RewriteRule.