I know that
xxxx is a number between 1-9000. How to brute force the range?
It isn't clear what you want to achieve by bruteforcing that range. That being said, the iteration process can be achieved with cURL alone.
curl -s "http://example.com/[1-9000].php"
Have a look at DirBuster. "DirBuster is a multi threaded java application designed to brute force directories and files names on web/application servers." It is pretty simple to set up a repeating attack like you describe.
The DirBuster tool is still available and comes with the kali distros, but the project's home page now says it's now been deprecated in favor of a newer tool, ZAP. ZAP looks like it has a lot more features; but I've never used it or figured out how to make it attack in the way you're asking.