How to clear previously echoed items in PHP

Question

In php, is there any way to clear/remove all previously echoed or printed items?

For example:

Answer 1

If a hacker let's say has access to your PHP file, he will also be able to remove the statement clearing the output buffer.

If you are doing this because you are letting your users upload PHP scripts, let me tell you that this is an extremely bad idea.

In both cases, doing what you are asking for adds 0 security.