htaccess redirect pages to specific subdomain

Question

Lets say I have a page at: foobar.com/application.php

I want any reference to foobar.com/application.php to redirect as www.foobar.com/application.php. I only want that rule to apply to the application.php page.

xyz.foobar.com/page1.php would not redirect. xyz.foobar.com/application.php would redirect to www.foobar.com/application.php.

(any subdomain except www).foorbar.com/application.php would redirect to www.

How can I form a htaccess rule that says when the application.php page is accessed to check the subdomain and if it's not www., then make it www.?

Examples for application.php page

1. www.foobar.com/application.php would NOT redirect since it is www
2. abc.foobar.com/application.php would redirect to www.
3. xyz.foobar.com/application.php would redirect to www.
4. whatever.foobar.com/application.php would redirect to www.
5. anything.foobar.com/application.php would redirect to www.
6. (anything here EXCEPT www) .foobar.com/application.php would redirect to www.

Answer 1

RewriteEngine On
RewriteCond %{HTTP_HOST} ^xyz.foobar.com$ [NC]
RewriteCond %{THE_REQUEST} /application\.php [NC]
RewriteRule ^(.*)$ http://www.foobar.com/$1 [NC,R,L]