Please provide the exact code needed to rewrite the pages from one
domain to another.  Currently we are hosting one web site and have
another domain name mirrored to the hosted one.  We believe this is
affecting our ranking in Google.  We have an unix-based server and the
mod_rewrite is enabled.

Example would be:

http://firstdomain.com/first_category/index.html

---> Redirects to:

http://otherdomain.com/first_category/index.html

The files, file structure, etc. are exactly the same.  In essence we
are just rewriting one domain to another.

Assuming that you are running Apache webserver with mod_rewrite
module; try adding these lines in your firstdomain.com virtualhost
configuration:

 RewriteEngine On
 RewriteRule ^/first_category/index.html
http://otherdomain.com/first_category/index.html [R]

Note: Make sure your rewrite rule is in single line with no line break.

Thanks. This works just fine!