How to deal with get data

The get data URL is 1.php? Direct echo & nbsp; $ a in the ax webpage; when Can x be output? when is the output blank? just tested? & nbsp; directly output x on the local machine, put it on the server is empty, don't know what God's law ------ solution ------------------ php has a configuration item register_globals, let $ a receive the value of $ _ GET [... the error message returned when get is missing.
The URL is 1.php? A = x


Directly on the webpage
Echo $;

When can I output x? When can I output null?

In the test just now, x is output directly on the machine, and x is left blank on the server.
------ Solution --------------------
Php has a configuration item register_globals that allows $ a to receive the value of $ _ GET ['A']... because the vulnerability is too large, it has been disabled by default for a long time.