g1smd - 2:16 pm on Apr 3, 2011 (gmt 0)
User's don't "receive content from a different URL".
Users request a URL and the server fetches a file to serve that content. URLs and files are not at all the same thing. Understanding this is the key to understanding what rewriting actually does.
Usually the file inside the server is the same file as suggested by the path part of the URL.
With a rewrite, the file is a different file to that suggested by the path part of the URL, the RewriteRule being the thing that does the "translation".
RewriteRule ^index\.php /Forums/portal.php [L]
In the above example, user requests the URL example.com/index.php and the server fetches the file at /Forums/portal.php instead of the file at /index.php.
The index.php part of the rule matches the literal
GET /index.php HTTP/1.1 request sent by the browser.
If you request www.example.com/ only, then that URL request will not be matched by that rule and it will not return the file you wanted.
A modified rule could do it
RewriteRule ^$ /Forums/portal.php [L]
Now it will return the portal page if you ask for example.com/ without a path.
However, in this case, if you are talking merely about the root URL and no other URLs within your site, there is a simpler way to achieve what you want: