Module 1: Introduction to PHP

What is PHP?

In this Introduction to PHP, we will explore one of the most popular programming languages on the web.PHP (which stands for Hypertext Preprocessor) is one of the most popular server-side scripting languages in the world. It is specifically designed for web development to create dynamic and interactive websites.

Unlike HTML, which can only show static content (content that stays the same), PHP allows a website to be dynamic—meaning the page can change based on user interaction, time of day, or database information. you can always check the official PHP documentation.

• Full Form: PHP: Hypertext Preprocessor
• Type: Server-Side Scripting (It runs on the web server, not on your browser).
• File Extension: All PHP files must end with .php.

Why Use PHP for Web Development?

Developers choose PHP because it powers over 75% of the web (including Facebook and WordPress).

• Dynamic Content: It generates fresh content automatically (e.g., displaying “Welcome, John” after a user logs in).
• Database Connectivity: It easily connects to databases like MySQL to store and retrieve user data.
• Enhanced Security: The backend logic is hidden. Users only receive the final HTML output, keeping your source code secure.

How PHP Works (The Request Lifecycle)

It is crucial for beginners to understand that PHP does not run in the browser. It follows a 3-step lifecycle:

1. The Request: A user types a URL (e.g., index.php) into their browser.
2. Server Processing: The web server (like Apache or Nginx) receives the request and executes the PHP script.
3. The Response: The server sends the result back to the browser as pure HTML. The user never sees the original PHP code.

PHP Syntax & “Hello World” Example

Every PHP script is enclosed within special start and end tags. This tells the server to start interpreting the code.

• Opening Tag: <?php
• Closing Tag: ?>

Code Example: Your First Script

PHP

<?php
  // This is a single-line comment
  echo "Hello, World!"; 
?>

Code Breakdown:

; (Semicolon): The terminator. Every PHP statement must end with a semicolon, or the code will produce an error.

<?php ... ?>: These tags act as a container for your code.

echo: A language construct used to output data to the screen.

"Hello, World!": The text string you want to display.

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