Variable Scope

Scope determines where in your script a variable can be accessed.

Syntaxglobal $variable;

The scope of a variable is the part of the script where it can be referenced.

A variable declared outside a function has global scope and cannot be used inside a function by default.
A variable declared inside a function has local scope.

To use a global variable inside a function, use the global keyword.

Example

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Keeping a function's temporary variables from leaking into the rest of the program.
Reading a global configuration value inside a function via the global keyword.
Preventing accidental overwrites of same-named variables in different functions.

Variables declared inside a function are invisible outside it.

<?php
function greet() {
    $msg = "Hi";
    echo $msg;
}
greet();
// echo $msg; // Error: $msg only exists inside greet()

global pulls an outer-scope variable into the function.

<?php
$appName = "SoundsCode";
function banner() {
    global $appName;
    echo "Welcome to $appName";
}
banner();

$GLOBALS holds every global by name — an alternative to the global keyword.

<?php
$count = 5;
function show() {
    echo $GLOBALS['count'];
}
show();