PHP is a general-purpose scripting language that is especially suited to server-side web development, in which case PHP generally runs on a web server. Any PHP code in a requested file is executed by the PHP runtime, usually to create dynamic web page content or dynamic images used on websites or elsewhere.[150] It can also be used for command-line scripting and client-sidegraphical user interface (GUI) applications. PHP can be deployed on most web servers, many operating systems and platforms, and can be used with many relational database management systems (RDBMS). Most web hosting providers support PHP for use by their clients. It is available free of charge, and the PHP Group provides the complete source code for users to build, customize and extend for their own use.[7]
PHP acts primarily as a filter,[151] taking input from a file or stream containing text and/or PHP instructions and outputting another stream of data. Most commonly the output will be HTML, although it could be JSON, XML or binary data such as image or audio formats. Since PHP 4, the PHP parsercompiles input to produce bytecode for processing by the Zend Engine, giving improved performance over its interpreter predecessor.[152]
Originally designed to create dynamic web pages, PHP now focuses mainly on server-side scripting,[153] and it is similar to other server-side scripting languages that provide dynamic content from a web server to a client, such as Microsoft's ASP.NET, Sun Microsystems' JavaServer Pages,[154] and mod_perl. PHP has also attracted the development of many software frameworks that provide building blocks and a design structure to promote rapid application development (RAD). Some of these include PRADO, CakePHP, Symfony, CodeIgniter, Laravel, Yii Framework, Phalcon and Zend Framework, offering features similar to other web frameworks.
The LAMP architecture has become popular in the web industry as a way of deploying web applications.[155] PHP is commonly used as the P in this bundle alongside Linux, Apache and MySQL, although the P may also refer to Python, Perl, or some mix of the three. Similar packages, WAMP and MAMP, are also available for Windows and OS X, with the first letter standing for the respective operating system. Although both PHP and Apache are provided as part of the Mac OS X base install, users of these packages seek a simpler installation mechanism that can be more easily kept up to date.
As of April 2007, over 20 million Internet domains had web services hosted on servers with PHP installed and mod_phpwas recorded as the most popular Apache HTTP Server module.[156] As of May 2017, PHP was used as the server-side programming language on 83% of 10 million most popular websites.[157]Web content management systemswritten in PHP include MediaWiki,[158]Joomla,[159] eZ Publish, eZ Platform, SilverStripe,[160] WordPress,[161]Drupal,[162] and Moodle.[163] Websites written in PHP, in back-end and/or user-facing portion, include Facebook,[164]Digg,[165] Tumblr,[166] Dailymotion,[167]and Slack.[168]
For specific and more advanced usage scenarios, PHP offers a well defined and documented way for writing custom extensions in C or C++.[169][170][171][172][173][174][175] Besides extending the language itself in form of additional libraries, extensions are providing a way for improving execution speed where it is critical and there is room for improvements by using a true compiled language.[176][177] PHP also offers well defined ways for embedding itself into other software projects. That way PHP can be easily used as an internal scripting language for another project, also providing tight interfacing with the project's specific internal data structures.[178]
PHP received mixed reviews due to lacking support for multithreading at the core language level,[179] though using threads is made possible by the "pthreads" PECL extension.[180][181]
As of January 2013, PHP was used in more than 240 million websites (39% of those sampled) and was installed on 2.1 million web servers.[182]
