How can robots show the original page, and redirect users to another address?

Question

PHP

It is necessary that after the visitor enters the page, the server sends him through a redirect to another address (how to do this is clear). But search robots show the original page without 301 responses so that the page does not drop out of the search.

Answer 1

Look at the user-agent header and, depending on what you see, redirect or not. But:
1. Search engines don't really like it when different things are given to bots and real people.
2. Many user agent crawlers cheat.
In general, this can be done without PHP, using a single web server.

Answer 2

Did you mean "so that the entire site is guaranteed to fly out of the search"?
Yes, it's a reliable way.

Answer 3

and how to get banned anyway) you can’t do this, and Google and Yandex have people - assessors, they periodically check the issuance with pens.