How to specify the path to the home directory in HTACCESS in one variable?

Question

htaccess

Hello. I am new to PHP. I wrote a php script, placed the file in the main directory on the hosting and I want it to be processed every time a person visits any page of my site.
To do this, I wrote the following in HTACCESS:

php_value auto_prepend_file /home/блаблабла/public_html/antiddos.php

The question is: is there any way to shorten the given string "/home/blablabla/public_html/" by replacing it with a single variable. Tried to do something similar:

php_value auto_prepend_file https://%{SERVER_NAME}/antiddos.php

But the site is down. What to do?