PHP & MySQL® Web Development All-in-One Desk Reference for Dummies®

1.1. How PHP Works

The PHP software works with the Web server. The Web server is the software that delivers Web pages to the world. When you type a URL into your Web browser's address bar, you're sending a message to the Web server at that URL, asking it to send you an HTML file. The Web server responds by sending the requested file. Your browser reads the HTML file and displays the Web page. You also request a file from the Web server when you click a link in a Web page. In addition, the Web server processes a file when you click a Web page button that submits a form.

NOTE

How the Web server processes PHP files When a browser is pointed to a regular HTML file with an .html or .htm extension, the Web server sends the file, as is, to the browser. The browser processes the file and displays the Web page described by the HTML tags in the file. When a browser is pointed to a PHP file (with a .php extension), the Web server looks for PHP sections in the file and processes them instead of just sending them as is to the browser. The Web server processes the PHP file as follows: The Web server starts scanning the file in HTML mode. It assumes the statements are HTML and sends them to the browser without any processing. The Web server continues in HTML mode until it encounters a PHP opening tag (<?php). When it encounters a PHP opening tag, the Web server switches to PHP mode. This is sometimes called escaping from HTML. The Web server then assumes that all statements are PHP statements ...