PHP Overview

What is PHP?

PHP (PHP: Hypertext Preprocessor) is a server-side scripting language designed specifically for web development. Created by Rasmus Lerdorf in 1995, it was originally a set of CGI scripts called "Personal Home Page" tools.

PHP's defining characteristic: it's designed to be embedded directly in HTML. This makes it a templating language as much as a programming language.

<!DOCTYPE html>
<html>
<body>
    <h1>Welcome</h1>
    <p>The time is: <?php echo date('H:i:s'); ?></p>
    <p>You are visitor #<?php echo $visitorCount; ?></p>
</body>
</html>

The server processes the <?php ... ?> blocks, replacing them with their output. The browser receives pure HTML.

How PHP Executes

PHP typically runs as an Apache module (mod_php) or via PHP-FPM (FastCGI Process Manager). Either way, the web server hands off .php files to the PHP interpreter.

PHP request flow with mod_php: Browser sends GET /index.php to Apache which contains an embedded PHP interpreter. The interpreter reads the file, parses PHP code, executes the logic, and generates HTML output that is returned to the browser.

Key point: Each PHP request starts fresh. Variables don't persist between requests (that's what sessions and databases are for).

Why PHP?

Despite jokes about its inconsistencies, PHP powers a remarkable portion of the web:

~77% of websites with a known server-side language use PHP
WordPress (43% of all websites) is built on PHP
Wikipedia, Facebook (originally), and countless others
Mature ecosystem: Composer packages, Laravel/Symfony frameworks
Easy deployment: Just upload .php files

For learning server-side concepts, PHP is excellent because:

The connection between URL and file is clear (/cart.php → cart.php)
Superglobals make request data obvious ($_GET, $_POST)
Sessions work out of the box (session_start())
No build step - just save and refresh

PHP Syntax Essentials

Variables and Output

<?php
// Variables start with $
$name = "Alice";
$count = 42;
$prices = [9.99, 14.99, 29.99];  // Array

// Output
echo "Hello, $name!";           // Prints: Hello, Alice!
echo "Count: " . $count;        // Concatenation with .
?>

Control Structures

<?php
// Conditionals
if ($age >= 18) {
    echo "Adult";
} elseif ($age >= 13) {
    echo "Teen";
} else {
    echo "Child";
}

// Loops
foreach ($items as $item) {
    echo "<li>$item</li>";
}
?>

Superglobals

PHP provides special arrays that are always available:

Superglobal	Contains	Example
`$_GET`	URL query parameters	`$_GET['id']` from `?id=42`
`$_POST`	Form data (POST method)	`$_POST['username']`
`$_SESSION`	Session data	`$_SESSION['user_id']`
`$_COOKIE`	Cookie values	`$_COOKIE['theme']`
`$_SERVER`	Server/request info	`$_SERVER['REQUEST_METHOD']`

Quick Reference: Common Operations

// Read form input safely
$username = $_POST['username'] ?? '';
$username = htmlspecialchars($username, ENT_QUOTES, 'UTF-8');

// Check request method
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    // Handle form submission
}

// Start a session
session_start();
$_SESSION['user_id'] = 42;

// Set a cookie (1 hour expiry)
setcookie('theme', 'dark', time() + 3600, '/');

// Redirect
header('Location: /dashboard.php');
exit;

// Return JSON
header('Content-Type: application/json');
echo json_encode(['status' => 'ok']);

Ready to Learn PHP?

Work through our hands-on tutorial with live demos.

Start the PHP Tutorial →

PHP in the Ecosystem

While this course focuses on PHP fundamentals, modern PHP development often involves:

Composer: Package manager (like npm for Node.js)
Frameworks: Laravel, Symfony, Slim for structured applications
ORMs: Eloquent, Doctrine for database abstraction
Testing: PHPUnit for automated tests
PHP 8+: Modern features like named arguments, attributes, JIT

The fundamentals you learn here apply regardless of framework choice.