.htaccess rewrite subdomain to directory and keep subdomain in url

I need to rewrite a subdomain to a subdirectory using .htaccess but keep the subdomain in the url like this:

Visited url in browser: sub1.domain.com

Served url: sub.domain.com/sub1/

I tried the following

RewriteCond %{HTTP_HOST} ^subdomain.domain.com
RewriteRule ^(.*)$ http://subdomain.domain.com/subdomain/$1 [L,NC,QSA]

but this leads to an endless loop. I know that it would be easier to do this by php but is there any solution for this with using .htaccess?

Answer

You can use this rule in document root:

RewriteCond %{HTTP_HOST} ^subdomain.domain.com$ [NC]
RewriteRule ^((?!sub1/).*)$ /sub1/$1 [L,NC]

Explanation:

• NC: Ignore case
• L: Last rule
• RewriteCond %{HTTP_HOST} line makes sure that rule only executes for subdomain
• (?!sub1/) is negative lookahead expression that means of request is not starting with /sub1/
• RewriteRule ^((?!sub1/).*)$ /sub1/$1 [L,NC] rewrites current path to /sub1/<uri>

References:

• Apache mod_rewrite Introduction
• Apache mod_rewrite Technical Details