The Bridge Between User and Server

Nearly every website you use needs to collect information from you. Whether you're using a search engine, logging into an account, or leaving a comment, you are interacting with an HTML Form. Forms are the primary way to send data from the user's browser (client-side) to the server (server-side), and PHP is excellent at processing this data.

The HTML Form Element

An HTML form is defined with the <form> tag. The two most important attributes of this tag are:

  • action: This specifies the path to the PHP file that will process the form data.
  • method: This specifies the HTTP method to be used. The two most common methods are GET and POST.
<form action="welcome.php" method="post">
    Name: <input type="text" name="username">
    <button type="submit">Submit</button>
</form>

GET vs. POST

Choosing the right method is important for functionality and security.

GET Method

When you submit a form with the GET method, the data is sent as URL parameters. You will see it in the browser's address bar.

http://example.com/search.php?query=php+tutorials

  • Visibility: All data is visible in the URL.
  • Limitations: There is a limit to the amount of data you can send (about 2000 characters).
  • Best for: Non-sensitive data, like search queries or page numbers. Should never be used for passwords or personal information.

POST Method

When you submit a form with the POST method, the data is sent in the body of the HTTP request. It is not visible in the URL.

  • Visibility: Data is hidden from the address bar.
  • Limitations: No limit on the amount of data you can send.
  • Best for: Sensitive information like logins, contact forms, and any data that modifies the database.

Processing Form Data in PHP

PHP makes it easy to access the data sent from a form using special built-in arrays called superglobals:

  • $_GET: An associative array containing data sent via the GET method.
  • $_POST: An associative array containing data sent via the POST method.

Example: A Simple Welcome Form

Let's create two files. Save the first as form.html and the second as welcome.php in your htdocs/php-course folder.

form.html:

<!DOCTYPE html>
<html>
<body>
<form action="welcome.php" method="post">
  Name: <input type="text" name="name"><br>
  Email: <input type="email" name="email"><br>
  <button type="submit">Submit</button>
</form>
</body>
</html>

welcome.php:

<?php
    // Use htmlspecialchars() to prevent security issues like XSS
    $name = htmlspecialchars($_POST["name"]);
    $email = htmlspecialchars($_POST["email"]);

    echo "Welcome, " . $name . "!<br>";
    echo "Your email address is: " . $email;
?>

Now, open http://localhost/php-course/form.html in your browser, fill out the form, and click submit. The welcome.php script will process your input and display a personalized greeting. You've just built your first interactive web feature!