global key word in a function

 
<?php
$a = 7;
function test() {
  global $a;
  $a = 20;
}
test();
echo "\$a = $a\n";
?>

1.	Create function from string
2.	Declaring a Simple Function
3.	Function printing text on a Web Page
4.	Declaring a Function
5.	A Simple User Function
6.	A Function Requiring Two Arguments
7.	A Function to Build Query Strings
8.	A function that calculates sales tax
9.	Accessing a Global Variable from Within a Function
10.	Build and then call a function
11.	Call the function
12.	Create a User Function
13.	Defining functions before or after calling them
14.	Creating and calling a function that accepts arguments
15.	Define constant in a function
16.	nesting functions
17.	Variables Defined Outside Functions Are Inaccessible from Within a Function by Default
18.	Using nested functions

global key word in a function : Definition « Functions « PHP