🌍 PHP Web Concepts – The Foundation of Dynamic PHP Web Applications

Understand the building blocks of PHP web development including HTTP methods, superglobals, client-server communication, and form workflows.

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🧲 Introduction – Why Web Concepts Matter in PHP

Before diving into PHP logic, it’s essential to understand how the web works under the hood. PHP doesn’t operate in isolation — it’s tightly integrated with HTTP protocols, browsers, servers, and user interactions.

🎯 In this guide, you’ll learn:

• The PHP client-server interaction model
• How PHP handles user data using GET/POST
• The role of superglobals in accessing request data
• Session and cookie handling in modern web flows

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🌐 The Client-Server Communication Model

Web applications follow a client-server model where:

1. A user (client) sends a request via a browser.
2. The server executes PHP scripts.
3. PHP generates HTML or JSON responses.
4. The response is sent back to the browser for display.

📎 PHP runs on the server and acts as the processing layer between browser requests and application logic.

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🔗 HTTP Request Methods – GET & POST

PHP handles incoming data using HTTP methods:

// Example usage
$username = $_GET['user'];  // From query string
$email = $_POST['email'];   // From submitted form

• ✅ $_GET — Data sent via the URL (query parameters).
• ✅ $_POST — Data sent in the HTTP request body (more secure and private).

🧠 Use GET for short queries and POST for sensitive or large data.

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📝 HTML Forms and PHP Interaction

Forms allow users to send data to your PHP scripts:

<form method="post" action="register.php">
  <input name="username" required>
  <input type="submit">
</form>

In PHP, access submitted data via:

$username = $_POST['username'];

➡️ PHP receives and processes user input using $_GET or $_POST depending on the form method.

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📦 PHP Superglobals Overview

Superglobals are built-in global arrays accessible from anywhere in your PHP scripts.

Superglobal	Purpose
$_GET	URL query parameters
$_POST	Form submission data
$_REQUEST	Combined GET, POST, and COOKIE data
$_FILES	Uploaded file data
$_COOKIE	Access cookies from the client
$_SESSION	Store user data on the server between pages
$_SERVER	Information about headers, paths, and script

🔒 Use $_POST or $_GET explicitly — avoid relying on $_REQUEST for security clarity.

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🔁 PHP Form Workflow Lifecycle

A typical form workflow includes:

1. Form creation using HTML.
2. PHP receives form input using $_POST or $_GET.
3. PHP sanitizes and validates the input.
4. If successful, the form is processed (e.g., data stored).
5. Apply Post-Redirect-Get (PRG) pattern to avoid re-submission.

Example PRG:

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
  // process input
  header("Location: thank-you.php");
  exit;
}

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🧼 Input Sanitization and Validation

Sanitize and validate all user input before using it:

$name = htmlspecialchars(trim($_POST["name"]));
$email = filter_var($_POST["email"], FILTER_VALIDATE_EMAIL);

✅ Use:

• htmlspecialchars() — escape HTML special characters
• filter_var() — validate/clean emails, URLs, integers, etc.

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⚙️ PHP Sessions for Persistent State

session_start();
$_SESSION['username'] = 'JohnDoe';

• Sessions persist user data across page loads
• Data is stored on the server
• Ideal for login states and user preferences

✅ Always call session_start() at the top of your script.

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🍪 PHP Cookies – Store on Client Side

setcookie("user", "JohnDoe", time() + 3600); // 1 hour expiry

• Cookies are stored in the user’s browser
• Used for remembering login info or preferences

Read cookies:

echo $_COOKIE["user"];

📌 Cookies are less secure than sessions — don’t store sensitive data.

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🔐 PHP Request Handling Best Practices

• ✅ Use POST for forms and sensitive data
• ✅ Sanitize every input
• ✅ Escape output to prevent XSS
• ✅ Avoid exposing raw superglobals to output
• ✅ Use HTTPS for encrypted communication

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📌 Summary – Recap & Next Steps

PHP Web Concepts provide the core infrastructure for processing requests, collecting form data, and maintaining user state. Mastery of these concepts ensures clean, secure, and efficient application flow.

🔍 Key Takeaways:

• PHP operates on a request-response cycle
• Superglobals enable access to HTTP and server data
• Forms use GET or POST to send data
• Sessions and cookies enable persistent user experience

⚙️ Real-World Use Cases:
Login systems, form submissions, shopping carts, preference management, contact forms

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❓ Frequently Asked Questions (FAQs)

❓ What is the difference between GET and POST in PHP?
✅ GET appends data to the URL (visible); POST sends data securely in the request body.

❓ Should I use $_REQUEST in modern applications?
❌ No. Use $_GET and $_POST explicitly for clarity and security.

❓ How do I store user data between page requests?
✅ Use $_SESSION to retain data server-side across pages.

❓ Are PHP sessions secure?
✅ Yes, if configured properly. Use HTTPS, regenerate session IDs, and validate session data.

❓ When should I use cookies instead of sessions?
✅ Use cookies for non-sensitive persistent data like “Remember Me” features.

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