Programming Tutorials

Different versions of PHP - History and evolution of PHP

By: Andi, Stig and Derick in PHP Tutorials on 2015-11-21  

It was eight years ago, when Rasmus Lerdorf first started developing PHP/FI. He could not have imagined that his creation would eventually lead to the development of PHP as we know it today, which is being used by millions of people. The first version of "PHP/FI," called Personal Homepage Tools/Form Interpreter, was a collection of Perl scripts in 1995. One of the basic features was a Perl-like language for handling form submissions, but it lacked many common useful language features, such as for loops.

A rewrite came with PHP/FI 2 in 1997, but at that time the development was almost solely handled by Rasmus. After its release in November of that year, Andi Gutmans and Zeev Suraski bumped into PHP/FI while looking for a language to develop an e-commerce solution as a university project. They discovered that PHP/FI was not quite as powerful as it seemed, and its language was lacking many common features. One of the most interesting aspects included the way while loops were implemented. The hand-crafted lexical scanner would go through the script and when it hit the while keyword it would remember its position in the file. At the end of the loop, the file pointer sought back to the saved position, and the whole loop was reread and re-executed.

Zeev and Andi decided to completely rewrite the scripting language. They then teamed up with Rasmus to release PHP 3, and along also came a new name: PHP: Hypertext Preprocessor, to emphasize that PHP was a different product and not only suitable for personal use. Zeev and Andi had also designed and implemented a new extension API. This new API made it possible to easily support additional extensions for performing tasks such as accessing databases, spell checkers and other technologies, which attracted many developers who were not part of the "core" group to join and contribute to the PHP project. At the time of PHP 3's release in June 1998, the estimated PHP installed base consisted of about 50,000 domains. PHP 3 sparked the beginning of PHP's real breakthrough, and was the first version to have an installed base of more than one million domains.

In late 1998, Zeev and Andi looked back at their work in PHP 3 and felt they could have written the scripting language even better, so they started yet another rewrite. While PHP 3 still continuously parsed the scripts while executing them, PHP 4 came with a new paradigm of "compile first, execute later." The compilation step does not compile PHP scripts into machine code; it instead compiles them into byte code, which is then executed by the Zend Engine (Zend stands for Zeev & Andi), the new heart of PHP 4. Because of this new way of executing scripts, the performance of PHP 4 was much better than that of PHP 3, with only a small amount of backward compatibility breakage.

Among other improvements was an improved extension API for better run-time performance, a web server abstraction layer allowing PHP 4 to run on most popular web servers, and lots more. PHP 4 was officially released on May 22, 2002, and today its installed base has surpassed 15 million domains. In PHP 3, the minor version number (the middle digit) was never used, and all versions were numbered as 3.0.x. This changed in PHP 4, and the minor version number was used to denote important changes in the language. The first important change came in PHP 4.1.0, which introduced superglobals such as $_GET and $_POST .

 Superglobals can be accessed from within functions without  having to use the global keyword. This feature was added in order to allow the register_globals INI option to be turned off. register_globals is a feature in PHP which automatically converts input variables like "?foo=bar" in http://php.net/?foo=bar to a PHP variable called $foo. Because many people do not check input variables properly, many applications had security holes, which made it quite easy to circumvent security and  authentication code.

With the new superglobals in place, on April 22, 2002, PHP 4.2.0 was released with the register_globals turned off by default. PHP 4.3.0, the last significant PHP 4 version, was released on December 27, 2002. This version introduced the Command Line Interface (CLI), a revamped file and network I/O layer (called streams), and a bundled GD library. Although most of those additions have no real effect on end users, the major version was bumped due to the major changes in PHP's core.

Soon after, the demand for more common object-oriented features increased immensely, and Andi came up with the idea of rewriting the objected-oriented part of the Zend Engine. Zeev and Andi wrote the "Zend Engine II: Feature Overview and Design" document and jumpstarted heated discussions about PHP's future. Although the basic language has stayed the same, many features were added, dropped, and changed by the time PHP 5 matured.

For example, namespaces and multiple inheritance, which were mentioned in the original document, never made it into PHP 5. Multiple inheritance was dropped in favor of interfaces, and namespaces were dropped completely. You can find a full list of new features in Chapter, "What Is New in PHP 5?" PHP 5 is expected to maintain and even increase PHP"s leadership in the web development market. Not only does it revolutionizes PHP"s objectoriented support but it also contains many new features which make it the ultimate web development platform.

The rewritten XML functionality in  PHP 5 puts it on par with other web technologies in some areas and overtakes them in others, especially due to the new SimpleXML extension which makes it ridiculously easy to manipulate XML documents. In addition, the new SOAP, MySQLi, and variety of other extensions are significant milestones in PHP's support for additional technologies.

PHP 6

PHP has received criticism due to lacking native Unicode support at the core language level, instead only supporting byte strings. In 2005, a project headed by Andrei Zmievski was initiated to bring native Unicode support throughout PHP, by embedding the International Components for Unicode (ICU) library, and representing text strings as UTF-16 internally.

In March 2010, the project in its current form was officially abandoned, and a PHP 5.4 release was prepared containing most remaining non-Unicode features from PHP 6, such as traits and closure re-binding.

PHP 7

During 2014 and 2015, a new major PHP version was developed, which was numbered PHP 7. The numbering of this version involved some debate. While the PHP 6 Unicode experiment had never been released, several articles and book titles referenced the PHP 6 name, which might have caused confusion if a new release were to reuse the name. After a vote, the name PHP 7 was chosen. The foundation of PHP 7 is a PHP branch that was originally dubbed PHP next generation (phpng). It was authored by Dmitry Stogov, Xinchen Hui and Nikita Popov, and aimed to optimize PHP performance by refactoring the Zend Engine to use more compact data structures with improved cache locality while retaining near-complete language compatibility.

Major versions of PHP are allowed to break backward-compatibility of code and therefore PHP 7 presented an opportunity for other improvements beyond phpng that require backward-compatibility breaks, including wider use of exceptions, reworking variable syntax to be more consistent and complete,[47] and the deprecation or removal of various legacy features.