📄 PHP Form Handling – Capture and Process User Input Securely

Learn how to build and manage HTML forms using PHP to collect, validate, and process user data safely and efficiently.

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🧲 Introduction – Why PHP Form Handling Matters

Forms are the backbone of user interaction on the web. Whether it’s user registration, login, feedback submission, or e-commerce checkout, forms allow data to flow from the browser to the server. PHP excels at handling this form data with precision, flexibility, and security.

🎯 In this guide, you’ll learn:

• How to create HTML forms that interact with PHP scripts
• How PHP receives and processes form data
• How to implement form validation and sanitation
• Security practices for preventing common vulnerabilities

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📄 PHP Form Handling

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

➡️ PHP reads the form inputs using $_POST or $_GET.
➡️ Always validate form data before using it.

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🔗 Handling Form Submission in PHP

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST['username'];
    echo "Hello, " . htmlspecialchars($username);
}

➡️ Use $_SERVER['REQUEST_METHOD'] to check for form submission.
➡️ Sanitize inputs with htmlspecialchars() to prevent XSS.

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🛡️ Validating Required Fields

if (empty($_POST["username"])) {
    echo "Username is required.";
}

➡️ Use empty() to ensure required fields aren’t skipped.
➡️ Display helpful messages for incomplete submissions.

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🧼 Sanitizing User Input

$username = trim($_POST["username"]);
$username = htmlspecialchars($username);

✅ Always:

• Remove whitespace (trim)
• Escape HTML (htmlspecialchars)
• Strip unwanted characters or tags (strip_tags if needed)

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🧪 Detecting the Form Method

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    // Handle the POST data
}

✅ Use conditionals to separate GET and POST behaviors.

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📤 Redirecting After Submission (PRG Pattern)

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

➡️ Prevents form resubmission when users refresh the page.

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✅ Complete Form Handling Workflow

1. User fills out an HTML form
2. Form submits to PHP script using POST or GET
3. PHP script checks request type
4. Input is validated and sanitized
5. Action is performed (e.g., save to DB)
6. User is redirected or shown a message

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📌 Summary – Recap & Next Steps

PHP form handling is at the heart of interactive and secure web applications. From simple input collection to full authentication flows, mastering forms enables you to build real-world web features.

🔍 Key Takeaways:

• Forms use POST or GET to send user data to PHP
• Validate and sanitize input to prevent security flaws
• Use $_POST, $_GET, and $_SERVER['REQUEST_METHOD']
• Use PRG pattern to prevent duplicate submissions

⚙️ Real-World Use Cases:
Login forms, feedback submission, contact pages, newsletter signup, surveys

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❓ Frequently Asked Questions (FAQs)

❓ How does PHP know a form was submitted?
✅ It checks $_SERVER['REQUEST_METHOD'] for POST or GET.

❓ Can I handle multiple form fields in one PHP file?
✅ Yes. Access them via $_POST['fieldname'] for each input.

❓ What is the difference between POST and GET?
✅ GET sends data in the URL, POST sends it securely in the request body.

❓ How can I retain form values after failed validation?
✅ Store the values in variables and repopulate the form using value="<?= htmlspecialchars($input) ?>".

❓ How do I prevent users from submitting malicious code?
✅ Sanitize input using htmlspecialchars() and validate with filter_var().

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