Function to stop PHP script from executing?

I'm trying to find a function that will allow me to totally stop executing a PHP script when it's called, without returning a value. I know about die(), exit(), etc, but those all return values. Thanks.

I dont understand what you mean.
Why call the script if you dont want it to run?
Under what circumstances to you want it to run or not run?

I don't want to send an extra packet from the server to the computer if i don't need to.

Wouldn't that mess with logging ?

I'm combining it with AJAX. The person viewing the webpage sends data to the PHP page. Then I want the PHP to do what it needs to, then completely stop so I don't need to send back a useless packet.

Instead of:

Client |>>>>>>>>>>>>>>>>>>>>>>>>>>>>>| Server
|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|

It's:

Client |>>>>>>>>>>>>>>>>>>>>>>>>>>>>>| Server

How do you know the server did what it needs to do if there's no response ?