How to include a file automatically in PHP?

I would like to have a "site.php" file (similar to Python) that is automatically included on every invocation, e.g. command-line execution or HTTP request. This file contains several important replacement functions which need to be available to both existing applications and new.

(I.e. I need to inclu开发者_StackOverflowde this file without modifying any files related to the applications in use.)

Is this possible? And if so, how?

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In php.ini set

auto_prepend_file="/path/to/site.php"

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EDITED - Read the initial post a bit too hastily, apologize.

In php.ini, instead..

auto_prepend_file="/path/to/site.php"