The first part of this book is a thorough discussion of PHP as a programming language. You will be introduced to common concepts of computer science and how they are implemented in PHP. No prior programming experience beyond the use of simple mark-up languages is necessary. That is, you must be familiar with HTML. These chapters focus on building a foundation of understanding rather than on how to solve specific problems. If you have experience programming in a similar language, such as C or Perl, you may choose to read
Chapter 1 and skim the rest, saving it as a reference. In most situations, PHP treats syntax much as these two languages do.
Chapter 1 is an introduction to PHP—how it began and what it looks like. It may be sufficient for experienced programmers, since it moves quickly through PHP's key features. If you are less experienced, I encourage you to treat this chapter as a first look. Don't worry too much about exactly how the examples work. I explain the concepts in depth in later chapters.
Chapter 2 introduces the concepts of variables, operators, and expressions. These are the building blocks of a PHP script. Essentially, a computer stores and manipulates data. Variables let you name values; operators and expressions let you manipulate them.
Chapter 3 examines the ways PHP allows you to control program execution. This includes conditional branches and loops.
Chapter 4 deals with functions, how they are called and how to define them. Functions are packages of code that you can call upon repeatedly.
Chapter 5 is about arrays—collections of values that are identified by either numbers or names. Arrays are a very powerful way to store information and retrieve it efficiently.
Chapter 6 is about classes, presenting an object-oriented approach to grouping functions and data. Although not strictly an object-oriented language, PHP supports many features found in OO languages such as Java.
Chapter 7 deals with how PHP sends and receives data. Files, network connections, and other means of communication are covered.
1.1 The Origins of PHP
Wonderful things come from singular inspiration. PHP began life as a simple way to track visitors to Rasmus Lerdorf's resume. It also could embed SQL queries in Web pages. But as often happens on the Web, admirers quickly asked for their own copies. As a proponent of the Internet's ethic of sharing, and as a generally agreeable person, Rasmus unleashed upon an unsuspecting Web his Personal Home Page Tools version 1.0.
"Unleashed upon himself" may be more accurate. PHP became very popular. A consequence was a flood of suggestions. PHP 1.0 filtered input, replacing simple commands for HTML. As its popularity grew, people wondered if it couldn't do more. Loops, conditionals, rich data structures—all the conveniences of modern structured programming seemed like a next logical step. Rasmus studied language parsers, read about YACC and GNU Bison, and created PHP 2, otherwise known as PHP/FI.
PHP/FI allowed developers to embed structured code inside HTML tags. PHP scripts could parse data submitted by HTML forms, communicate with databases, and make complex calculations on the fly. And it was very fast because the freely available source code compiled into the Apache Web server. A PHP script executed as part of the Web server process and required no forking, often a criticism of Common Gateway Interface (CGI) scripts.
PHP was a legitimate development solution and began to be used for commercial Web sites. In 1996, Clear Ink created the SuperCuts site (
www.supercuts.com) and used PHP to create a custom experience for the Web surfer. The PHP Web site tracks the popularity of PHP by measuring how many different Web sites use the PHP module. When writing the second edition of this text, it seemed really exciting that PHP had grown from 100,000 sites to 350,000 sites during 1999. The most recent data show more than 10 million domains using PHP!
In 1997, a pair of Israeli students named Andi Gutmans and Zeev Suraski attempted to use it for building an online shopping cart, considered cutting-edge enough to be a university project. Shortly after they started, they stumbled upon various bugs in PHP that made them look under the hood at the source code. To their surprise, they noticed that PHP's implementation broke most of the principles of language design, which made it prone to unexpected behavior and bugs. Always looking for good excuses not to study for exams, they started creating a new implementation. In part, the task was a test of their programming abilities, in part a recreation. A few months later, they had rewritten PHP from scratch, making it a real, consistent, and robust language for the first time. Having spent so much time on the project, they asked the course teacher, Dr. Michael Rodeh, for academic credit in an attempt to avoid unnecessary exams. Being the manager of the IBM Research Lab in Haifa and well aware of the overwhelming number of different languages to choose from, he agreed—with the stipulation that they cooperate with the existing developers of PHP/FI instead of starting their own language.
When Andi and Zeev emailed Rasmus with the news about their rewrite, they wondered if he would accept this new work, as it essentially meant discarding his implementation. Rasmus did accept it, and a new body was formed—the PHP Core Team, known today as the PHP Group. Along with Andi, Rasmus, and Zeev, three other developers—Stig Bakken, Shane Caraveo, and Jim Winstead—were accepted to the Core Team. A community of developers started growing around PHP.
After seven months of development, alpha and beta testing, PHP version 3.0 was officially released on June 6, 1998, and started bending the curve of PHP's growth to unprecedented angles. PHP's functionality was growing on a daily basis, and PHP applications were popping up everywhere. Following the release, Open Source projects written in PHP flourished. Projects like Phorum tackled long-time Internet tasks such as hosting online discussion. The PHPLib project provided a framework for handling user sessions that inspired new code in PHP. FreeTrade, a project I led, offered a toolkit for building e-commerce sites.
Writing about PHP increased as well. More than 20 articles appeared on high-traffic sites such as
webmonkey.com and
techweb.com. Sites dedicated to supporting PHP developers were launched. The first two books about PHP were published in May 1999. Egon Schmid, Christian Cartus, and Richard Blume wrote a book in German called
PHP: Dynamische Webauftritte professionell realisieren. Prentice Hall published the first edition of my book,
Core PHP Programming. Since then, countless books about PHP fill bookstore shelves.
Given this background, there were no reasons not to be happy with the way PHP was back then. Perhaps the internal knowledge of what was going on under the hood and the feeling familiar to every developer—"I could have done it much better"—were the reasons that Andi and Zeev were some of the very few people who felt unhappy with PHP 3. As if out of habit, they withdrew from the PHP community and attempted to design a new approach towards executing PHP scripts.
A few months later, on January 4, 1999, Zeev and Andi announced a new framework that promised to increase dramatically the performance of PHP scripts. They dubbed the new framework the Zend Engine. Early tests showed script execution times dropping by a factor of 100. In addition, new features for compiling scripts into binary, debugging, optimization, and profiling were planned. This announcement officially ended the PHP 3.1 project, which was supposed to bring better Windows support to PHP 3 but failed to gain momentum, and officially started the planning of PHP 4.
Work on the Zend Engine and PHP 4 continued in parallel with bug fixes and enhancements to PHP 3. During 1999, eight incremental versions were released, and on December 29, 1999, PHP version 3.0.13 was announced. A PHP beta based on the Zend Engine became publicly available in July 19, 1999, and was followed by an intense development period of various components, some of which were brand new, such as built-in session handling, output buffering, and a Web server abstraction layer. The release of PHP 4 on May 22, 2000, marked another important milestone on PHP's journey to becoming the most popular Web development platform on earth. The number of people working on various levels of PHP has grown immensely, and new projects, most notably PEAR, gained momentum and started pushing PHP to new heights of popularity.
The PHP community drives the development of new features. Many programmers find inspiration in object-oriented programming. PHP 3 introduced objects as syntactic sugar. That is, while the syntax used for objects was different, the underlying implementation varied little from arrays. It attracted many object-oriented advocates, but the limited implementation left them desiring more. PHP 5 addresses these needs with a strong, rebuilt object system.
