PHP Academy · Lesson

Variable Scope: Local and Global

Understand how PHP isolates function scope and how to use the global keyword.

Variable Scope: Local and Global is a free PHP Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the PHP Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Variable Scope in PHP

In PHP every variable has a scope — the region of code where it is accessible.

Variables created outside functions are in global scope
Variables created inside functions are in local scope
PHP does NOT have block scope (unlike C or JavaScript)

Local Scope

Variables inside a function are local — they disappear when the function returns:

<?php
function compute(): void {
    $result = 42;  // local variable
    echo $result;  // 42
}

compute();
echo $result ?? 'undefined';  // undefined — $result is gone

Global Variables Are NOT Auto-Visible

Unlike many languages, PHP functions cannot see global variables by default — you must explicitly import them:

<?php
$message = 'Hello';

function printMessage(): void {
    echo $message ?? 'not visible';  // 'not visible'
    // $message from global scope is not accessible here
}

The global Keyword

Use global $varName inside a function to access a global variable:

<?php
$counter = 0;

function increment(): void {
    global $counter;
    $counter++;
}

increment();
increment();
echo $counter;  // 2

$GLOBALS Superglobal

$GLOBALS is an array that holds all global variables — accessible anywhere without the global keyword:

<?php
$total = 100;

function addTax(): void {
    $GLOBALS['total'] *= 1.18;  // 18% tax
}

addTax();
echo $total;  // 118

Why Avoid global

Overusing global creates hidden dependencies — functions become hard to test and debug. Prefer passing values as arguments:

<?php
// Bad
$db = new PDO(/* ... */);
function getUsers(): array {
    global $db;
    return $db->query('SELECT * FROM users')->fetchAll();
}

// Good
function getUsers(PDO $db): array {
    return $db->query('SELECT * FROM users')->fetchAll();
}

Static Variables

A static variable retains its value between function calls but is still local to the function:

<?php
function callCount(): int {
    static $count = 0;
    return ++$count;
}

echo callCount();  // 1
echo callCount();  // 2
echo callCount();  // 3

Closures and Variable Capture

Closures (anonymous functions) can capture outer variables with use:

<?php
$prefix = 'Mr';

$greet = function(string $name) use ($prefix): string {
    return "$prefix. $name";
};

echo $greet('Smith');  // Mr. Smith

Capture by Reference

Capture by reference with use (&$var) so the closure can modify the outer variable:

<?php
$total = 0;

$add = function(int $n) use (&$total): void {
    $total += $n;
};

$add(10);
$add(5);
echo $total;  // 15

Arrow Functions

PHP 7.4 arrow functions (fn =>) automatically capture outer scope by value — no use needed:

<?php
$multiplier = 3;
$nums = [1, 2, 3, 4];

$result = array_map(fn($n) => $n * $multiplier, $nums);

print_r($result);  // [3, 6, 9, 12]

Nested Functions

PHP allows defining a function inside another, but the inner function becomes globally accessible after the outer is called:

<?php
function outer(): void {
    function inner(): void {
        echo 'inner called';
    }
}

// inner(); // Fatal: undefined before outer() is called
outer();
inner(); // works now

Quick Check

What does a static variable inside a PHP function do?

Recap: Variable Scope

Key scope rules in PHP:

Functions have their own local scope
Global variables must be imported with global
Use $GLOBALS['name'] as an alternative
static variables persist across calls within a function
Closures capture outer vars with use
Arrow functions auto-capture by value

Frequently asked questions

Is the “Variable Scope: Local and Global” lesson free?

Yes — the full text of “Variable Scope: Local and Global” is free to read here on the web, and the PHP Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the PHP Academy course, upgrade to CoddyKit PRO.

What will I learn in “Variable Scope: Local and Global”?

Understand how PHP isolates function scope and how to use the global keyword. You practise PHP Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start PHP Academy?

No prior experience is required. PHP Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Variable Scope: Local and Global” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this PHP Academy lesson?

Yes. Every PHP Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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