How to correctly check and prevent the file from executing during a direct call?

Question

1C-Bitrix

Let's say I put function files in the libs folder and include them in several pages. But how to check that the access to these files was direct (for example, site.ru/libs/functions.php) and prohibit their execution outside the connection in other files?

Answer 1

Well, the usual way is to define a variable of type $access = true in index, and check in the included file:
if (!isset($access) || !$access) exit();

Answer 2

Deny access to the libs folder (if access is needed only from within).
You need to throw .htaccess into libs:
deny from all