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PHP

(Redirected from PHP programming language)
For the "PHP" Cold-war history project, see Parallel History Project.

PHP (a recursive acronym for "PHP: Hypertext Preprocessor") is a widely-used open-source programming language primarily for server-side applications and developing dynamic web content. Famous examples of PHP applications include phpBB and MediaWiki, the software behind Wikipedia. The PHP model can be seen as an alternative to Microsoft's ASP/VBScript/JScript system, Macromedia's ColdFusion system, Sun Microsystems' JSP/Java system, and to the CGI/Perl system.

PHP logo
PHP logo

PHP's ease of use and similarity with the most common structured programming languages – most notably C and Perl (and from version 5, Java) – allows most experienced programmers to start developing complex applications with a minimal learning curve. It also enables experienced developers to get involved with dynamic web content applications without having to learn a whole new set of functions and practices.

One of the more attractive parts of PHP is that it is more than just a scripting language. Thanks to its modular design, PHP is also used to develop GUI applications (using PHP-GTK), and can be used from the command line just like Perl or Python.

PHP allows easy interaction with a large number of relational database systems, such as Oracle, DB2, MySQL, and PostgreSQL, while maintaining a simple and straightforward syntax. PHP runs on most major operating systems, including UNIX, Linux, Windows, and Mac OS X, and can interact with many major web servers. The official PHP website contains extensive documentation. The Linux, Apache, MySQL, PHP (LAMP) architecture has become very popular in the Web industry as a way of deploying inexpensive, reliable, scalable, secure web applications. (The 'P' in LAMP can also stand for Perl or Python.)

PHP is the result of the collective efforts of many contributors. It is licensed under a BSD-style license, the PHP license. PHP, from version 4, has been powered by the Zend engine.

Contents
1 History
2 Popularity
3 Code example
4 PHP's libraries
5 Object-oriented programming
6 Caching and optimization
7 Criticism of PHP
8 Support
9 Software built with PHP
10 External links

10.1 PHP homepage
10.2 Advocacy
10.3 Frameworks
10.4 Integrated development environments and debuggers

10.4.1 IDEs
10.4.2 Debuggers (all have profiling features)

10.5 Security
10.6 Tutorials and articles

History

PHP was originally designed as a small set of Perl scripts, followed by a rewritten set of CGI binaries written in C by Rasmus Lerdorf in 1994 to display his résumé and collect some data, such as how many hits it was generating. Others first used "Personal Home Page Tools" in 1995, when Lerdorf had combined it with his own Form Interpreter to create PHP/FI. Zeev Suraski and Andi Gutmans , two Israeli developers of the Technion - Israel Institute of Technology, rewrote the parser in 1997 and formed the base of PHP 3. They also changed the name to its current recursive form. After months in beta, the development team officially released PHP/FI 2 in November 1997. Public testing of PHP 3 began immediately and the official launch came in June 1998. Suraski and Gutmans then started a new rewrite of PHP's core, producing the Zend engine in 1999 (a page at www.zend.com [1] states that PHP 3 was powered by Zend Engine 0.5). In May 2000, PHP 4, powered by the Zend Engine 1.0, was released. On July 13, 2004, PHP 5 was released, powered by Zend Engine II (formerly known as Zend Engine 2).

Popularity

PHP is currently one of the most popular server-side scripting systems on the Web. It has been widely adopted since the release of version 4, which was the first version powered by the powerful Zend Engine.

One major part of PHP which has helped it become popular is that it is a very loose language; in particular, it is dynamically typed. That is, the rules aren't as strict with variables—they don't have to be declared and they can hold any type of object. Further, unlike many other languages (like C++ and Java), arrays are able to hold objects of varying types, including other arrays. All of this "looseness" makes it very easy to do many things.

According to Netcraft's April 2002 survey, PHP is now the most deployed server-side scripting language, running on around 9 of the 37 million domains in their survey. This is confirmed by PHP's own figures, which show PHP usage (measured on a per-domain basis) growing at around 5% per month. In May 2003, almost 13 million domains were using PHP, based on the same source.[2]

Due to PHP's popularity, a new breed of programmer has emerged – one who is only familiar with PHP, which in turn forced open the door toward a command line interface for PHP, along with support for GUI library such as GTK+ and text mode libraries like ncurses and newt. This is a major step for PHP, because it represents its beginning adoption as a genuine programming language (i.e. running autonomously on a stand-alone machine, as opposed to its original purpose of serving web pages to client machines from a server).

Code example

Here is an example that prints out the lyrics for the song 99 Bottles of Beer:

<?php
 /*
 * This is a comment. Other ways of commenting are // and # symbols.
 * This /* kind of comment does not need stars (*) in the beginning
 * of each line but including them is a common practice. // and # comments
 * only comment the text that are after them in the same line and have no
 * special ending character.
 */

/*
 * First we define a new function called "plural".
 * It will return an "s" if the argument passed to it was any other
 * than number 1.
 */
 function plural($number) {
   return ($number != 1 ? "s" : "");
   // The ternary operation above is a conditional structure similar to if-else: (condition ? true : false)
}

// We define a variable called $l to contain an HTML line break
// as well as a carriage return and line feed:
 $l = "<br />\r\n";

 for ($i = 99; $i > 0; $i--) {
    print "$i bottle" . plural($i) . " of beer on the wall,$l";
    // We don't actually need a new print for each line. Let's see:
    print "$i bottle" . plural($i) . " of beer.$l
           Take one down, pass it around,$l" .
           ($i - 1 != 0 ? $i - 1 : "no more") .
           " bottle" . plural($i - 1) . " of beer on the wall.$l$l";

    /*
    * PHP allows you to put strings on multiple lines, as long as
    * it eventually finds a semicolon (;) to terminate it.
    * A period (.) joins (concatenates) strings together.
    * Variables, the $-symbol things, are parsed (interpolated)
    * inside double quotation marks ("), but wouldn't be parsed
    * inside single quotation marks ('). Functions, such as
    * plural(), are not parsed inside any quotation marks.
    */
 }

print "Go to the store,$l buy some more,$l 99 bottles of beer on the wall!";

 ?>

PHP's libraries

PHP, unlike ASP, has some of the largest free and open-source libraries included with the core build. PHP is a fundamentally Internet-aware system and as such, there are modules built in for accessing FTP servers, all manners of database servers, embedded SQL libraries like embedded MySQL and SQLite, LDAP servers and much more. In addition to this, many familiar C functions such as the printf family are all available in the standard PHP build.

PHP has a wide variety of extensions such as support for the Windows API, process management on UNIX-like operating systems, cURL, and the ZIP/gzip/bzip2/rar/lzf compression formats. Some of the more unusual features are PDF generation, on-the-fly Macromedia Flash generation, integration with Internet relay chat and much more. Some additional extensions are available via the PHP Extension Community Library (PECL).

This is the present list of all officially documented libraries:

(Source: PHP.net manual)

Object-oriented programming

Up until version 3, PHP had no object-oriented features. In version 3 basic object functionality was added. The same semantics were implemented in PHP 4 as well as pass-by-reference and return-by-reference for objects but the implementation still lacked the powerful and useful features of other object-oriented languages like C++ and Java.

In version 5, which was released in July 2004, PHP's object-oriented functionality has been very much enhanced and is more robust and complete. Here is a summary of some of the changes in PHP 5 (powered by Zend Engine II):

  • New Object Model — PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or pass as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).
  • Private and Protected Members — PHP 5 introduces private and protected member variable s, they allow you to define the visibility of class properties.
  • Private and Protected Methods — Private and protected methods are also introduced.
  • Abstract Classes and Methods — PHP 5 also introduces abstract classes and methods. An abstract method only declares the method's signature and does not provide an implementation. A class that contains abstract methods needs to be declared abstract.
  • Interfaces — A class may implement an arbitrary list of interfaces.
  • Object Cloning — If the developer asks to create a copy of an object by using the reserved word clone, the Zend engine will check if a __clone() method has been defined or not. If not, it will call a default __clone() which will copy all of the object's properties. If a __clone() method is defined, then it will be responsible to set the necessary properties in the created object. For convenience, the engine will supply a function that imports all of the properties from the source object, so that they can start with a by-value replica of the source object, and only override properties that need to be changed.
  • Unified Constructors — PHP 5 introduces a standard way of declaring constructor methods by calling them by the name __construct().
  • Destructors — PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as Java: When the last reference to an object is destroyed, the object's destructor (a class method named __destruct() that receives no parameters) is called before the object is freed from memory.
  • Exceptions — PHP 4 had no exception handling. PHP 5 introduces a exception model similar to that of other programming languages.

More additions and examples of the additions mentioned above are available on this page.

Caching and optimization

Performance of PHP can, at times, be problematic since every time a script is executed, it and all files it uses are being compiled into byte-code, which is later executed by the Zend Engine. A number of PHP cache systems exist to speed up PHP processing by keeping the byte-code in RAM or on hard disk. Some examples include:

Criticism of PHP

PHP is widely used and widely admired for the tasks it performs. Like any language, however, it has its detractors. Some of the more common criticisms of PHP are as follows:

  • The syntax is alleged to be inelegant.
    • Built-in function names have no standard form, with some employing underscores (strip_tags) while others do not (stripslashes).
    • Within sections of the built-in function selection there is little or no consistency regarding argument order (examples: order of subject array and other data for array handling functions, order of needle and haystack in various search functions).
  • Some functions have inconsistent output. Statements like This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE, such as 0 or "". can be found in the documentation [3]. This is related to PHP's dynamic typing.
  • In some areas the selection of built-in functions is notably incomplete (supplying intersection and union functions, but no full difference function, for example).
  • The number of built-in functions is said to be too numerous, with many functions performing the same actions, but with just slightly different data, results, etc. This is said to make it difficult to program in the language without the frequent consultation of a reference work.
    • There are over 3,000 functions, sharing the same global namespace.
  • Some default settings and features are said to be confusing and the cause of frequent errors.
    • There is a "magic-quotes" feature that inserts backslashes into user-input strings. The feature was introduced to reduce code written by beginners from being dangerous, (such as in SQL injection attacks), but some criticize it as a frequent cause of improperly displayed text.
  • Error messages are said to be confusing; however, this is a common criticism alleged against many, if not all, programming languages.

Criticism of PHP also includes those general criticisms ascribed to other scripting programming languages and dynamically typed languages.

Support

Although the PHP development team does not provide programming help directly, there are many excellent help resources available for the novice PHP programmer. Worth mentioning are the PHP mailing lists (also available on PHP.net's news server), the Usenet group comp.lang.php, and the IRC channels #php and #phphelp on EFNet, IRCNet, DALnet and other networks. There is also a PHP user group registry. Other IRC channels include #php and #phpfreaks on freenode and also #phpcafe on irc.invisionize.com. Additionally, online forum communities have sprung up around PHP support, such as Devshed and PHPBuilder.

Software built with PHP

The following is list of notable software developed using PHP that's not already noted above: CMSformE, Drupal, Gallery Project, Invision Power Board, Moodle, PhpLDAPadmin, phpMyAdmin, PHP-Nuke, PostNuke, phpPgAdmin, PhpWiki, Pmachine, PmWiki, PostNuke, PunBB, Smarty, Typo3, UBB.threads, vBulletin, WordPress, Xaraya, XOOPS.

External links

 Our sister project, Wikibooks, provides an electronic book on PHP.


PHP homepage

Advocacy

Frameworks

  • Achievo ATK - Achievo ATK is an open source framework that allows a programmer to focus on business logic rather than HTML coding.
  • Ampoliros - Advanced distributed PHP web applications platform, featuring an XML-RPC and SOAP interface.
  • Copix Framework - Developer-oriented PHP framework offering a 5-layer architecture (site & documentation in French).
  • CreaLabs MerlinWork - Fully OO PHP framework for building stateful web applications.
  • DotPHP - Framework that wants to be like ASP.NET.
  • Eocene - Simple OO web development framework for PHP and ASP.NET.
  • Fusebox for PHP
  • LogiCreate - PHP web application server and framework.
  • Mojavi Project - Open-source MVC (Model-view-controller) framework for PHP.
  • PEAR - Open-source framework and distribution system for reusable PHP components.
  • phpHtmlLib - Set of PHP classes and library functions to help facilitate building, debugging, and rendering of XML, HTML, XHTML, WAP/WML Documents, and SVG (Scalable Vector Graphics) images as well as complex html 'widgets'.
  • php.MVC - Open source framework for PHP web applications that implements the MVC design pattern.
  • Phrame - Web development platform that encourages application architectures based on the "Model2" approach.
  • Plankton Web Application Framework - Integrated collection of classes that provide the building blocks and underlying architecture for an entire PHP web application.
  • Roadsend SiteManager - Open source web application framework for PHP Developers that includes a framework for code modules and layout templates, database connectivity, SmartForms, sessions, and other tools.
  • Web Application Component Toolkit - Modular patterns based framework for creating high performance web applications.
  • Yawp - Yet Another Web Programming foundation for PHP applications.

Integrated development environments and debuggers

IDEs

Debuggers (all have profiling features)

Security

Tutorials and articles


Last updated: 10-24-2004 05:10:45