PHP originally stood for “Personal Home Page” as it was created in 1994 by Rasmus Lerdorf to  rack the visitors to his online résumé. As its usefulness and capabilities grew (and as it started  eing used in more professional situations), it came to mean “PHP: Hypertext Preprocessor.” According to the official PHP Web site, found at www.php.net . PHP is a “widely-used  eneral-purpose scripting language that is especially suited for Web development and can be  mbedded into HTML.” It’s a long but descriptive definition, whose meaning I’ll explain. Starting at  he end of that statement, to say that PHP can be embedded into HTML means that you can take    tandard HTML page, drop in some PHP wherever you need it, and end up with a dynamic result.  his attribute makes PHP very approachable for anyone that’s done even a little bit of HTML work.

PHP is a scripting language, as opposed to a programming language: PHP was designed to write Web scripts, not standalone applications (although, with some extra effort, you can now create applications in PHP). PHP scripts run only after an event occurs—for example, when a user submits a form or goes to a URL.I should add to this definition that PHP is a server-side, cross-platform technology, both descriptions being important. Server-side refers to the fact that everything PHP does occurs on the server. A Web server application, like Apache or Microsoft’s IIS (Internet Information Services), is required and all PHP scripts must be accessed through a URL (http://-something). Its cross-platform nature means that PHP runs on most operating systems, including Windows, Unix (and its many variants), and Macintosh. More important, the PHP scripts  ritten on one server will normally work on another with little or no modification. At the time the book was written, PHP was at version 5.2.4, with version 4.4.7 still being maintained. Support for version 4 is being
dropped, though, and it’s recommended that everyone use at least version 5 of PHP. If you’re still using version 4, you really should upgrade. If that’s not in your plans, then please grab the second edition of this book instead. If you’re using PHP 5, either the second or this edition of the book will work for you. In this edition, I will make
it clear which features and functions are PHP 6–specific.

What’s new in PHP 6

Because of the planned extinction of PHP 4, many users and Web hosting companies will likely make a quick transition from PHP 4 to PHP 5 to PHP 6. To discuss what’s new in PHP 6, I’ll start with the even bigger differences between PHP 4 and 5.

PHP 5, like PHP 4 before it, is a major new development of this popular programming language. The most critical changes in PHP 5 involve object-oriented programming (OOP). the biggest change in PHP 5 is the addition of the Improved MySQL Extension, which is used to communicate with MySQL. The Improved MySQL Extension offers many benefits over the older MySQL extension and will be used exclusively.

The big change in PHP 6 is support for Unicode, which is to say that PHP can now handle characters in every language in the world. This is huge, and it’s also one of the reasons it’s taken a while to release PHP 6.  What this means in terms of programming is covered in Chapter 14, “Making Universal Sites.” The information in that chapter is also used in Chapter 15, “Example—Message Board.” Beyond Unicode support, PHP 6 cleans up a lot of garbage that was left in PHP 5 even though the recommendation was not to use such things. The two biggest removals are the “Magic Quotes” and “register globals” features.

How PHP works

As previously stated, PHP is a server-side language. This means that the code you write in PHP sits on a host computer called a server.  The server sends Web pages to the requesting visitors (you, the client, with your Web browser).