How PHP works

PHP is an embedded scripting language when used in Web pages. This means that PHP code is embedded in HTML code. You use HTML tags to enclose the PHP language that you embed in your HTML file — the same way that you would use other HTML tags. You create and edit Web pages containing PHP the same way that you create and edit regular HTML pages. 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, 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 the Web server to send you a file 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.
When PHP is installed, the Web server is configured to expect certain file extensions to contain PHP language statements. Often the extension is .php or .phtml, but any extension can be used. When the Web server gets a request for a file with the designated extension, it sends the HTML statements as-is, but PHP statements are processed by the PHP software before they’re sent to the requester.
When PHP language statements are processed, only the output is sent by the Web server to the Web browser. The PHP language statements are not included in the output sent to the browser, so the PHP code is secure and transparent to the user. For instance, in this simple PHP statement:

Hello World”; ?>

is the closing tag. echo is a PHP instruction that tells PHP to output the upcoming text. The PHP software processes the PHP statement and outputs this:

Hello World

which is a regular HTML statement. This HTML statement is delivered to the user’s browser. The browser interprets the statement as HTML code and displays a Web page with one paragraph — Hello World. The PHP statement is not delivered to the browser, so the user never sees any PHP statements. PHP and the Web server must work closely together. PHP is not integrated with all Web servers but does work with many of the popular Web servers. PHP is developed as a project of the Apache Software Foundation — thus, it works best with Apache. PHP also works with Microsoft IIS/PWS, iPlanet (formerly Netscape Enterprise Server), and others. Although PHP works with several Web servers, it works best with Apache. If you can select or influence the selection of the Web server used in your organization, select Apache. By itself, Apache is a good choice. It is free, open source, stable, and popular. It currently powers more than 60 percent of all Web sites, according to the Web server survey at www.netcraft.com. It runs on Windows, Linux, Mac OS, and most flavors of Unix.

Advantages of PHP

The popularity of PHP is growing rapidly because of its many advantages:

• It’s fast. Because it is embedded in HTML code, the response time is short.
• It’s inexpensive — free, in fact. PHP is proof that free lunches do exist and that you can get more than you paid for.
• It’s easy to use. PHP contains many special features and functions needed to create dynamic Web pages. The PHP language is designed to be included easily in an HTML file.
• It can run on many operating systems. It runs on a variety of operating systems — Windows, Linux, Mac OS, and most varieties of Unix.
• Technical support is widely available. A large base of users provides free support through e-mail discussion lists.
• It’s secure. The user does not see the PHP code.
• It’s designed to support databases. PHP includes functionality designed to interact with specific databases. It relieves you of the need to know the technical details required to communicate with a database.
• It’s customizable. The open source license allows programmers to modify the PHP software, adding or modifying features as needed to fit their own specific environments.

PHP, a Data Mover

PHP, a scripting language designed specifically for use on the Web, is your tool for creating dynamic Web pages. Rich in features that make Web design and programming easier, PHP is in use on more than 20 million domains (according to the Netcraft survey at www.php.net/usage.php). Its popularity continues to grow, so it must be fulfilling its function pretty well. PHP stands for PHP: HyperText Preprocessor. In its early development by a guy named Rasmus Lerdorf, it was called Personal Home Page tools. When it developed into a full-blown language, the name was changed to be more in line with its expanded functionality.
The PHP language’s syntax is similar to the syntax of C, so if you have experience with C, you’ll be comfortable with PHP. PHP is actually simpler than C because it doesn’t use some of the more difficult concepts of C. PHP also doesn’t include the low-level programming capabilities of C because PHP is designed to program Web sites and doesn’t require those capabilities. PHP is particularly strong in its ability to interact with databases. PHP supports pretty much every database you’ve ever heard of (and some you haven’t). PHP handles connecting to the database and communicating with it. You don’t need to know the technical details for connecting to a database or for exchanging messages with it. You tell PHP the name of the database and where it is, and PHP handles the details. It connects to the database, passes your instructions to the database, and returns the database response to you. Technical support is available for PHP. You can join one of several e-mail discussion lists offered on the PHP Web site (www.php.net), including a list for databases and PHP. In addition, a Web interface to the discussion lists is available at news.php.net, where you can browse or search the messages.