How to generate a 404 error for all search engines?

Question

Search Engine Optimization

How to issue a 404 error for all search engines on a certain file, but not for users?
How is it technically implemented?

Answer 1

1) check useragent
2) return 404
list of agents:
www.useragentstring.com/pages/Crawlerlist
see googlebot, bingbot, yandex, baidu, Mail.Ru Bot

Answer 2

You need robots.txt . Settings may vary for different search engines, so go ahead and read the documentation for the ones you need.