How to block all possible search bots?

Question

PHP

There is a task to block access to indexing by all possible search engines and their spiders/bots.
I want to do it the right way.
I'm currently thinking about something like this:

$ua = $_SERVER['HTTP_USER_AGENT'];
if(mb_strpos($ua, "bot") || mb_strpos($ua, "crawler") || mb_strpos($ua, "spider")){
header("Location: some.url");
}
else{
...
Содержимое страницы
...
}

But I'm not sure that this is correct or that all possible options are taken into account.

Answer 1

what's the point? normal search engines react to a ban in robots.txt, and abnormal ones can have any UA.