I would like to add a function to PHP so I can use it in any script that runs on my server. Is it possible to register a function like if it was native from PHP? Does PHP has some kind of configuration file where I can register new global / native functions?
There is no intentions to use it in production, I'm just curious on how to achieve this.
You could use a "Global include" (defined in php.ini)
Read this (php.net manual)
You can write extensions in C or C++, in particular write or use library bindings with SWIG or FFI. But that's a bit effort, and only advisable if you meant compiled "native" functions.
The lazy option to add new core functions to PHP via config is the auto_prepend_file= php.ini setting. That allows to register a script that gets executed before everything else. (I use that for fixing magic quotes on some servers, or always having phpquery available for CLI testing.)
There is a full chapter in the manual http://www.php.net/manual/en/internals2.php devoted to writing extensions to php, with examples.
The easiest way is to write them in PHP and include them before your scripts is executed using
auto_prepend_file = /path/to/file.php
http://php.net/manual/en/ini.core.php
else you need to learn C and write a extension
