PHP Overview

Server-Side Scripting for the Web

"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."

CSE 135 — Full Overview | Review Questions

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Section 1What is PHP?

A server-side language designed to be embedded in HTML.

History & The Embedded Model

Created by Rasmus Lerdorf in 1995 as "Personal Home Page" tools. PHP (PHP: Hypertext Preprocessor) is designed to be embedded directly in HTML.

<!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 <?php ?> blocks, replacing them with output. The browser receives pure HTML — it never sees PHP code. This makes PHP a templating language as much as a programming language.

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Section 2How PHP Executes

The mod_php request flow and the per-request model.

mod_php Request Flow

Request Flow with mod_php: ┌─────────┐ ┌───────────────────────────────────────┐ │ Browser │ │ Apache + mod_php │ │ │ GET /index.php │ ┌─────────────────────────────────┐ │ │ │ ──────────────────▶│ │ PHP Interpreter │ │ │ │ │ │ │ │ │ │ │ │ 1. Read index.php │ │ │ │ │ │ 2. Parse PHP code │ │ │ │ │ │ 3. Execute (run logic) │ │ │ │ │ │ 4. Generate HTML output │ │ │ │ HTML response │ │ │ │ │ │ ◀──────────────────│ └─────────────────────────────────┘ │ └─────────┘ └───────────────────────────────────────┘

PHP runs inside Apache as a module. Apache receives the request, hands the .php file to the PHP interpreter, and returns the generated HTML.

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Per-Request Execution

Each PHP request starts fresh. Variables don't persist between requests. When the response is sent, everything is destroyed. That's what sessions and databases are for.

PHP (per-request)

Process starts on each request
Variables created
Logic executes
HTML generated
Process ends — everything gone

Node.js (persistent)

Process starts once
Variables persist in memory
app.listen(3000)
Handles many requests
Runs until you stop it

This is the fundamental architectural difference. PHP runs inside a web server and processes one request at a time. Node.js IS the server and runs continuously.

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Section 3Why PHP?

Market dominance and learning advantages.

Market Share & Learning Benefits

Market Dominance

~77% of websites with a known server-side language use PHP
WordPress (43% of all websites) is built on PHP
Wikipedia, Facebook (originally) use PHP
Mature ecosystem: Composer, Laravel, Symfony

Why Learn PHP?

URL-to-file mapping: /cart.php → cart.php
Superglobals: $_GET, $_POST make request data obvious
Built-in sessions: session_start() just works
No build step: Save and refresh

Easy deployment: just upload .php files. No npm install, no process managers, no build steps. This makes the connection between code and result immediate and clear.

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Section 4PHP Syntax Essentials

Variables, control structures, superglobals, and common operations.

Variables & Control Structures

Variables & Output

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

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

Control Structures

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

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

Variables start with $, strings use . for concatenation, and double-quoted strings interpolate variables directly.

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Superglobals & Quick Reference

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']`

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

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

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

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

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Section 5PHP in the Ecosystem

Composer, frameworks, ORMs, testing, and PHP 8+.

Modern PHP Development

Composer: Package manager (like npm for Node.js) — manages dependencies via composer.json
Frameworks: Laravel, Symfony, Slim for structured, MVC-based applications
ORMs: Eloquent (Laravel), Doctrine (Symfony) for database abstraction
Testing: PHPUnit for automated unit and integration tests
PHP 8+: Named arguments, attributes, union types, fibers, JIT compilation

The fundamentals apply regardless of framework choice. Understanding how PHP processes requests, reads superglobals, and generates output is the foundation that every framework builds upon.

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SummaryKey Takeaways

5 concepts of PHP server-side development in one table.

PHP Overview at a Glance

Concept	Key Takeaway
What is PHP?	A server-side language embedded in HTML. The server processes `<?php ?>` blocks and the browser receives pure HTML.
Execution Model	PHP runs inside Apache (mod_php). Each request starts fresh — variables don't persist. Sessions and databases handle state.
Why PHP?	~77% market share, WordPress, simple deployment. URL-to-file mapping and superglobals make concepts transparent.
Syntax Essentials	`$` variables, superglobals (`$_GET`, `$_POST`, `$_SESSION`), and built-in functions for sessions, cookies, and JSON.
Ecosystem	Composer, Laravel/Symfony, Eloquent/Doctrine, PHPUnit, PHP 8+. Fundamentals apply regardless of framework.

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