Apache config or .htaccess, ban on entering the site via a direct link?

Question

Apache HTTP Server

Hello, please tell me how to implement such a scheme. It is
necessary that when you enter the site.ru site (entering the site address into the browser line), a page for example 404 is displayed, but if you enter the site from a search engine, the main page of the site is displayed.
I've seen this on several projects.

Answer 1

SetEnvIfNoCase User-Agent .*google.* search_robot
SetEnvIfNoCase User-Agent .*yahoo.* search_robot
SetEnvIfNoCase User-Agent .*bot.* search_robot
SetEnvIfNoCase User-Agent .*ask.* search_robot

Order Deny,Allow
Deny from All
Allow from env=search_robot

searched on google in a few seconds

Answer 2

RewriteEngine on 
RewriteCond %{HTTP_REFERER} ^$ 
RewriteRule^- [F,L]