Question

How to configure PHP to emit warning when I try to read value of unset variable?

It is frequently happens when I rename variable in one place, I obtain weird result because I forgot to rename it in other place.

Answer 1

Set error reporting to all and you will get info about any undefined variables too, for example, put this on top of your script:

ini_set('display_errors', true);
error_reporting(E_ALL);