PHP file protection from direct access

Question

I was reading some WordPress PHP code on GitHub, and I found that the author (a senior WordPress developer) put this line of code at the top of each file:

defined('ABSPATH') or die("Cannot access pages directly.");

How does this protect the file from direct access? Could a hacker determine the ABSPATH constant and then download the file?

Also, why is direct access dangerous?

Answer 1

This constant is probably set in the main WordPress PHP file, so if it is not set, you will not get access to the main page.

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Answer 2

defined('ABSPATH') or die("Cannot access pages directly.");   

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