Say you want to use .htaccess URL rewriting to make sure that example.com always redirects to www.example.com (or vice-versa). Or something more complicated that depends on the host name.
You want to test it before you upload to your production server, but your staging server has a different URL (obviously).
An easy trick is to use curl, manually setting the Host: header to simulate access through different URLs. For example, assume your test server is at IP address 1.2.3.4 and you want to make sure that example.com redirects to www.example.com. Type this:
curl --head --header "Host: example.com" http://1.2.3.4/
The –head option fetches only the headers. The –header option spoofs the Host: header with the value that would have been sent by a browser accessing your production site.
If your .htaccess is correct, you should get output like this:
HTTP/1.1 301 Moved Permanently Date: Wed, 02 Feb 2011 18:47:54 GMT Server: Apache/2.2.14 Location: http://www.example.com/
If the HTTP code on the first line is 301 and you have a Location field with the expected URL, it worked!
If you see “HTTP/1.1 200 OK” then the server just served up a regular page. If you see “HTTP/1.1 500 Internal Server Error” then something went horribly wrong.
Armed with this knowledge, a clever person could write a script to automate these tests, confirming that all the redirects work as expected before deploying the site.