PHP

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Template:About Template:Good article Template:Infobox programming language

PHP is a server-side scripting language designed for web development but also used as a general-purpose programming language. Template:As of, PHP was installed on more than 240 million websites (39% of those sampled) and 2.1 million web servers.<ref>Template:Cite web</ref> Originally created by Rasmus Lerdorf in 1994,<ref name="History of PHP">Template:Cite web</ref> the reference implementation of PHP (powered by the Zend Engine) is now produced by The PHP Group.<ref name="about PHP">Template:Cite web</ref> While PHP originally stood for Personal Home Page,<ref name="History of PHP" /> it now stands for PHP: Hypertext Preprocessor, which is a recursive backronym.<ref>PHP Manual: Preface, www.php.net</ref>

PHP code can be simply mixed with HTML code, or it can be used in combination with various templating engines and web frameworks. PHP code is usually processed by a PHP interpreter, which is usually implemented as a web server's native module or a Common Gateway Interface (CGI) executable. After the PHP code is interpreted and executed, the web server sends resulting output to its client, usually in form of a part of the generated web pageTemplate:Snd for example, PHP code can generate a web page's HTML code, an image, or some other data. PHP has also evolved to include a command-line interface (CLI) capability and can be used in standalone graphical applications.<ref>Template:Cite web</ref>

The canonical PHP interpreter, powered by the Zend Engine, is free software released under the PHP License. PHP has been widely ported and can be deployed on most web servers on almost every operating system and platform, free of charge.<ref name="foundations" />

Despite its popularity, no written specification or standard exists for the PHP language; instead, the canonical PHP interpreter serves as a de facto standard. However, work on creating a formal specification has started in 2014.<ref>Template:Cite web</ref>

History

Template:Multiple image

PHP development began in 1994 when Rasmus Lerdorf wrote a series of Common Gateway Interface (CGI) binaries in C,<ref name="about PHP"/><ref>Template:Cite web</ref><ref> Template:Cite web</ref><ref>Template:Cite web </ref> which he used to maintain his personal homepage. He extended them to add the ability to work with web forms and to communicate with databases, and called this implementation "Personal Home Page/Forms Interpreter" or PHP/FI.

PHP/FI could be used to build simple, dynamic web applications. Lerdorf initially announced the release of PHP/FI as "Personal Home Page Tools (PHP Tools) version 1.0" publicly to accelerate bug location and improve the code, on the Usenet discussion group comp.infosystems.www.authoring.cgi on June 8, 1995.<ref> Template:Cite web</ref><ref>Template:Cite newsgroup</ref> This release already had the basic functionality that PHP has Template:As of. This included Perl-like variables, form handling, and the ability to embed HTML. The syntax resembled that of Perl but was simpler, more limited and less consistent.<ref name="about PHP"/>

Early PHP was not intended to be a new programming language, and grew organically, with Lerdorf noting in retrospect: "I don’t know how to stop it, there was never any intent to write a programming language […] I have absolutely no idea how to write a programming language, I just kept adding the next logical step on the way."<ref name=itconversations>Template:Cite web, cited at Template:Cite web</ref> A development team began to form and, after months of work and beta testing, officially released PHP/FI 2 in November 1997.

Template:Anchor One criticism of PHP is that it was not originally designed, but instead it was developed organically;<ref name=itconversations /> among other things, this has led to inconsistent naming of functions and inconsistent ordering of their parameters.<ref>Template:Cite web</ref> In some cases, the function names were chosen to match the lower-level libraries which PHP was "wrapping",<ref>Template:Cite web</ref> while in some very early versions of PHP the length of the function names was used internally as a hash function, so names were chosen to improve the distribution of hash values.<ref name="php-internals-70691">Template:Cite newsgroup</ref>

Zeev Suraski and Andi Gutmans rewrote the parser in 1997 and formed the base of PHP 3, changing the language's name to the recursive acronym PHP: Hypertext Preprocessor.<ref name="about PHP"/> Afterwards, public testing of PHP 3 began, 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.<ref>Template:Cite web</ref> They also founded Zend Technologies in Ramat Gan, Israel.<ref name="about PHP"/>

On May 22, 2000, PHP 4, powered by the Zend Engine 1.0, was released.<ref name="about PHP"/> As of August 2008 this branch reached version 4.4.9. PHP 4 is no longer under development nor will any security updates be released.<ref name="2007 news">Template:Cite web</ref><ref>Template:Cite web</ref>

On July 13, 2004, PHP 5 was released, powered by the new Zend Engine II.<ref name="about PHP"/> PHP 5 included new features such as improved support for object-oriented programming, the PHP Data Objects (PDO) extension (which defines a lightweight and consistent interface for accessing databases), and numerous performance enhancements.<ref>Template:Cite web</ref> In 2008 PHP 5 became the only stable version under development. Late static binding had been missing from PHP and was added in version 5.3.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

Many high-profile open-source projects ceased to support PHP 4 in new code as of February 5, 2008, because of the GoPHP5 initiative,<ref name="gophp5_projects">Template:Cite web</ref> provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.<ref name="gophp5">Template:Cite web</ref><ref>Template:Cite web</ref>

Over time, PHP interpreters became available on most existing 32-bit and 64-bit operating systems, either by building them from the PHP source code, or by using pre-built binaries.<ref>Template:Cite web</ref> For the PHP versions 5.3 and 5.4, the only available Microsoft Windows binary distributions were 32-bit x86 builds,<ref>Template:Cite web</ref><ref>Template:Cite web</ref> requiring Windows 32-bit compatibility mode while using Internet Information Services (IIS) on a 64-bit Windows platform. PHP version 5.5 made the 64-bit x86-64 builds available for Microsoft Windows.<ref>Template:Cite web</ref>

Template:AnchorPHP 6 and Unicode

PHP received mixed reviews due to lacking native Unicode support at the core language level.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> 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.<ref>Template:Cite web</ref> Since this would cause major changes both to the internals of the language and to user code, it was planned to release this as version 6.0 of the language, along with other major features then in development.<ref>Template:Cite web</ref>

However, a shortage of developers who understood the necessary changes, and performance problems arising from conversion to and from UTF-16, which is rarely used in a web context, led to delays in the project.<ref>Template:Cite web</ref> As a result, a PHP 5.3 release was created in 2009, with many non-Unicode features back-ported from PHP 6, notably namespaces. 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.<ref>Template:Cite web</ref> Initial hopes were that a new plan would be formed for Unicode integration, but as of 2014 none has been adopted.

Template:AnchorPHP 7

Template:As of, work is underway on a new major PHP version named PHP 7. There was some dispute as to whether the next major version of PHP was to be called PHP 6 or PHP 7. While the PHP 6 unicode experiment had never been released, a number of articles and book titles referenced the old PHP 6 name, which might have caused confusion if a new release were to reuse the PHP 6 name.<ref>Template:Cite web</ref> After a vote, the name PHP 7 was chosen.<ref>Template:Cite web</ref>

PHP 7 gets its foundations from an experimental PHP branch that was originally named PHPNG (PHP Next Generation), which aims at optimizing PHP performance by refactoring the Zend Engine while retaining near-complete language compatibility. Template:As of, WordPress-based benchmarks, which serve as the main benchmark suite for PHPNG project, show an almost 100% increase in performance.<ref>Template:Cite web</ref> Changes from PHPNG are also expected to make it easier to improve performance in the future, as more compact data structures and other changes are seen as better suited for a successful migration to a just-in-time (JIT) compiler.<ref>https://wiki.php.net/rfc/phpng</ref>

PHP 7 will also contain an improved variable syntax which is internally consistent and complete, resolving a long-standing issue in PHP. This will allow use of ->, [], (), {}, and :: operators with arbitrary meaningful left-hand-side expressions.<ref>Template:Cite web</ref>

Release history

Key
Color Meaning Development
Red Old release No development
Yellow Stable release Security fixes
Green Stable release Bug and security fixes
Blue Future release New features
Version Release date Supported until<ref>Template:Cite web</ref> Notes
1.0 Template:Date Officially called "Personal Home Page Tools (PHP Tools)". This is the first use of the name "PHP".<ref name="about PHP"/>
2.0 Template:Date Officially called "PHP/FI 2.0". This is the first release that could actually be characterised as PHP, being a standalone language with many features that have endured to the present day.
3.0 Template:Date Template:Date Development moves from one person to multiple developers. Zeev Suraski and Andi Gutmans rewrite the base for this version.<ref name="about PHP"/>
4.0 Template:Date Template:Date Added more advanced two-stage parse/execute tag-parsing system called the Zend engine.<ref name="php4changelog">Template:Cite web</ref>
4.1 Template:Date Template:Date Introduced 'superglobals' ($_GET, $_POST, $_SESSION, etc.)<ref name="php4changelog" />
4.2 Template:Date Template:Date Disabled register_globals by default. Data received over the network is not inserted directly into the global namespace anymore, closing possible security holes in applications.<ref name="php4changelog" />
4.3 Template:Date Template:Date Introduced the command-line interface (CLI), to supplement the CGI.<ref name="php4changelog" /><ref name="phpclidocs">Template:Cite web</ref>
4.4 Template:Date Template:Date Fixed a memory corruption bug, which required breaking binary compatibility with extensions compiled against PHP version 4.3.x.<ref name="php44announcement">Template:Cite web</ref>
5.0 Template:Date Template:Date Zend Engine II with a new object model.<ref name="php5changelog">Template:Cite web</ref>
5.1 Template:Date Template:Date Performance improvements with introduction of compiler variables in re-engineered PHP Engine.<ref name="php5changelog" /> Added PHP Data Objects (PDO) as a consistent interface for accessing databases.<ref name="phpPdoDocs">Template:Cite web</ref>
5.2 Template:Date Template:Date Enabled the filter extension by default. Native JSON support.<ref name="php5changelog" />
5.3 Template:Date Template:Date Namespace support; late static bindings, jump label (limited goto), closures, PHP archives (phar), garbage collection for circular references, improved Windows support, sqlite3, mysqlnd as a replacement for libmysql as underlying library for the extensions that work with MySQL, fileinfo as a replacement for mime_magic for better MIME support, the Internationalization extension, and deprecation of ereg extension.
5.4 Template:Date September 2015<ref>Template:Cite web</ref> Trait support, short array syntax support. Removed items: register_globals, safe_mode, allow_call_time_pass_reference, session_register(), session_unregister() and session_is_registered(). Built-in web server.<ref>Template:Cite web</ref> Several improvements to existing features, performance and reduced memory requirements.
5.5 Template:Date June 2016<ref name="releaseprocess"/> Support for generators, finally blocks for exceptions handling, OpCache (based on Zend Optimizer+) bundled in official distribution.<ref name="55changes">Template:Cite web</ref>
5.6 Template:Date August 2017<ref name="releaseprocess"/> Constant scalar expressions, variadic functions, argument unpacking, new exponentiation operator, extensions of the use statement for functions and constants, new phpdbg debugger as a SAPI module, and other smaller improvements.<ref name="56changes">Template:Cite web</ref>

Beginning on June 28, 2011, the PHP Group began following a timeline for when new versions of PHP will be released.<ref name="releaseprocess">Template:Cite web</ref> Under this timeline, at least one release should occur every month. Once per year, a minor release should occur which can include new features. Every minor release should at least have 2 years of security and bug fixes, followed by at least 1 year of only security fixes, for a total of a 3 year release process for every minor release. No new features (unless small and self-contained) will be introduced into a minor release during the 3-year release process.

Template:AnchorMascot

The mascot of the PHP project is the elePHPant,<ref>Template:Cite web</ref> a blue (sometimes differently colored when in plush toy form) elephant with the PHP logo on its side.

  • Elephpant.png

    The ElePHPant, PHP mascot

  • ElePHPant studying notes from SugarCon 2007.jpg

    A plush toy elePHPant

Syntax

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The following Hello world program is written in PHP code embedded in an HTML document:

<source lang="php"> <!DOCTYPE html> <html> 

   <head>
       <title>PHP Test</title>
   </head>
   <body>

<?php echo '

Hello World

'; ?> 

   </body>

</html> </source>

However, as PHP does not need to be embedded in HTML or used with a web server, the simplest version of a Hello World program can be written like this, with the closing tag omitted as preferred in files containing pure PHP code<ref>Template:Cite web</ref> (prior to PHP 5.4.0, this short syntax for echo() only works with the short_open_tag configuration setting enabled, while for PHP 5.4.0 and later it is always available):<ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref name="rfc-shortags">Template:Cite web</ref>

<source lang="php"> <?= 'Hello world'; </source>

The PHP interpreter only executes PHP code within its delimiters. Anything outside its delimiters is not processed by PHP (although non-PHP text is still subject to control structures described in PHP code). The most common delimiters are <?php to open and ?> to close PHP sections. <script language="php"> and </script> delimiters are also available, as are the shortened forms <? or <?= (which is used to echo back a string or variable) and ?> as well as ASP-style short forms <% or <%= and %>. Short delimiters make script files less portable, since support for them can be disabled in the local PHP configuration, and they are therefore discouraged.<ref name="rfc-shortags" /><ref name="basic syntax">Template:Cite web</ref> The purpose of all these delimiters is to separate PHP code from non-PHP code, including HTML.<ref>Template:Cite web</ref>

The first form of delimiters, <?php and ?>, in XHTML and other XML documents, creates correctly formed XML "processing instructions".<ref>Template:Cite web</ref> This means that the resulting mixture of PHP code and other markup in the server-side file is itself well-formed XML.

Template:Anchor Variables are prefixed with a dollar symbol, and a type does not need to be specified in advance. PHP 5 introduced type hinting that allows functions to force their parameters to be objects of a specific class, arrays, interfaces or callback functions. However, type hints can not be used with scalar types such as integer or string.<ref>Template:Cite web</ref>

Unlike function and class names, variable names are case sensitive. Both double-quoted ("") and heredoc strings provide the ability to interpolate a variable's value into the string.<ref>Template:Cite web</ref> PHP treats newlines as whitespace in the manner of a free-form language, and statements are terminated by a semicolon.<ref>Template:Cite web</ref> PHP has three types of comment syntax: /* */ marks block and inline comments; // as well as # are used for one-line comments.<ref>Template:Cite web</ref> The echo statement is one of several facilities PHP provides to output text, e.g., to a web browser.

In terms of keywords and language syntax, PHP is similar to most high level languages that follow the C style syntax. if conditions, for and while loops, and function returns are similar in syntax to languages such as C, C++, C#, Java and Perl.

Data types

PHP stores whole numbers in a platform-dependent range, either a 64-bit or 32-bit signed integer equivalent to the C-language long type. Unsigned integers are converted to signed values in certain situations; this behavior is different from other programming languages.<ref>Template:Cite web</ref> Integer variables can be assigned using decimal (positive and negative), octal, hexadecimal, and binary notations.

Floating point numbers are also stored in a platform-specific range. They can be specified using floating point notation, or two forms of scientific notation.<ref name="types">Template:Cite web</ref> PHP has a native Boolean type that is similar to the native Boolean types in Java and C++. Using the Boolean type conversion rules, non-zero values are interpreted as true and zero as false, as in Perl and C++.<ref name="types" />

The null data type represents a variable that has no value; NULL is the only allowed value for this data type.<ref name="types" />

Variables of the "resource" type represent references to resources from external sources. These are typically created by functions from a particular extension, and can only be processed by functions from the same extension; examples include file, image, and database resources.<ref name="types" />

Arrays can contain elements of any type that PHP can handle, including resources, objects, and even other arrays. Order is preserved in lists of values and in hashes with both keys and values, and the two can be intermingled.<ref name="types" /> PHP also supports strings, which can be used with single quotes, double quotes, nowdoc or heredoc syntax.<ref>Template:Cite web</ref>

The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes.<ref>Template:Cite web</ref>

Functions

PHP has hundreds of functions provided by the core language functionality and thousands more available via various extensions; these functions are well documented in the online PHP documentation.<ref name="functions" /> However, the built-in library has a wide variety of naming conventions and associated inconsistencies, as described under history above.

Additional functions can be defined by the developer:

<source lang="php"> function myAge($birthYear) // defines a function, this one is named "myAge" { 

   $yearsOld = date('Y') - $birthYear;                          // calculates the age
   return $yearsOld . ' year' . ($yearsOld != 1 ? 's' : );    // returns the age in a descriptive form

}

echo 'I am currently ' . myAge(1981) . ' old.'; // outputs the text concatenated 

                                                                // with the return value of myAge()

// As the result of this syntax, myAge() is called. // In 2014, the output of this sample program will be 'I am currently 33 years old.' </source>

In PHP, normal functions are not first-class and can only be referenced by their name directly, or dynamically by a variable containing the name of the function (referred to as "variable functions"). User-defined functions can be created at any time without being prototyped.<ref name="functions">Template:Cite web</ref><ref name="variable-functions">Template:Cite web</ref> Functions can be defined inside code blocks, permitting a run-time decision as to whether or not a function should be defined. Function calls must use parentheses, with the exception of zero-argument class constructor functions called with the PHP new operator, where parentheses are optional.

Until PHP 5.3, support for true anonymous functions or closures did not exist in PHP. While create_function() exists since PHP 4.0.1, it is merely a thin wrapper around eval() that allows normal PHP functions to be created during program execution.<ref>Template:Cite web</ref> Also, support for variable functions allows normal PHP functions to be used, for example, as callbacks or within function tables.<ref name="variable-functions" /> PHP 5.3 added support for closures, which are true anonymous, first-class functions,<ref>Template:Cite web</ref> whose syntax can be seen in the following example:

<source lang="php"> function getAdder($x) { 

   return function($y) use ($x)
   {
       return $x + $y;
   };

}

$adder = getAdder(8); echo $adder(2); // prints "10" </source>

In the example above, getAdder() function creates a closure using passed argument $x (the keyword use imports a variable from the lexical context), which takes an additional argument $y, and returns the created closure to the caller. Such a function is a first-class object, meaning that it can be stored in a variable, passed as a parameter to other functions, etc.<ref>Template:Cite web</ref>

The goto flow control statement is used as in the following example:

<source lang="php"> function lock() { 

   $file = fopen('file.txt', 'r+');

retry: 

   if (!flock($file, LOCK_EX | LOCK_NB))
       goto retry;

   fwrite($file, 'Success!');
   fclose($file);

} </source>

When flock() is called, PHP opens a file and tries to lock it. The target label retry: defines the point to which execution should return if flock() is unsuccessful and goto retry; is called. The goto statement is restricted and requires that the target label be in the same file and context.

The goto statement has been supported since PHP 5.3.

Objects

Basic object-oriented programming functionality was added in PHP 3 and improved in PHP 4.<ref name="about PHP"/> Object handling was completely rewritten for PHP 5, expanding the feature set and enhancing performance.<ref name="php 5 objects" /> In previous versions of PHP, objects were handled like value types.<ref name="php 5 objects">Template:Cite web</ref> The drawback of this method was that the whole object was copied when a variable was assigned or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value.

PHP 5 introduced private and protected member variables and methods, along with abstract classes, final classes, abstract methods, and final methods. It also introduced a standard way of declaring constructors and destructors, similar to that of other object-oriented languages such as C++, and a standard exception handling model. Furthermore, PHP 5 added interfaces and allowed for multiple interfaces to be implemented. There are special interfaces that allow objects to interact with the runtime system. Objects implementing ArrayAccess can be used with array syntax and objects implementing Iterator or IteratorAggregate can be used with the foreach language construct. There is no virtual table feature in the engine, so static variables are bound with a name instead of a reference at compile time.<ref name="zend engine 2">Template:Cite web</ref>

If the developer creates a copy of an object using the reserved word clone, the Zend engine will check whether a __clone() method has been defined. If not, it will call a default __clone() which will copy the object's properties. If a __clone() method is defined, then it will be responsible for setting the necessary properties in the created object. For convenience, the engine will supply a function that imports the properties of the source object, so the programmer can start with a by-value replica of the source object and only override properties that need to be changed.<ref>Template:Cite web</ref>

The following is a basic example of object-oriented programming in PHP:

<source lang="php"> class Person { 

   public $firstName;
   public $lastName;

   public function __construct($firstName, $lastName = ) { // optional second argument
       $this->firstName = $firstName;
       $this->lastName  = $lastName;
   }

   public function greet() {
       return 'Hello, my name is ' . $this->firstName .
              (($this->lastName != ) ? (' ' . $this->lastName) : ) . '.';
   }

   public static function staticGreet($firstName, $lastName) {
       return 'Hello, my name is ' . $firstName . ' ' . $lastName . '.';
   }

}

$he = new Person('John', 'Smith'); $she = new Person('Sally', 'Davis'); $other = new Person('iAmine');

echo $he->greet(); // prints "Hello, my name is John Smith." echo '
';

echo $she->greet(); // prints "Hello, my name is Sally Davis." echo '
';

echo $other->greet(); // prints "Hello, my name is iAmine." echo '
';

echo Person::staticGreet('Jane', 'Doe'); // prints "Hello, my name is Jane Doe." </source>

The visibility of PHP properties and methods is defined using the keywords public, private, and protected. The default is public, if only var is used; var is a synonym for public. Items declared public can be accessed everywhere. protected limits access to inherited classes (and to the class that defines the item). private limits visibility only to the class that defines the item.<ref>Template:Cite web</ref> Objects of the same type have access to each other's private and protected members even though they are not the same instance. PHP's member visibility features have sometimes been described as "highly useful."<ref>Template:Cite web</ref> However, they have also sometimes been described as "at best irrelevant and at worst positively harmful."<ref>Template:Cite web</ref>

Implementations

The original, only complete and most widely used PHP implementation is powered by the Zend Engine and known simply as PHP. To disambiguate it from other implementations, it is sometimes unofficially referred to as "Zend PHP". The Zend Engine compiles PHP source code on-the-fly into an internal format that it can execute, thus it works as an interpreter.<ref>Template:Cite web</ref><ref>Template:Harv</ref> It is also the "reference implementation" of PHP, as PHP has no formal specification, and so the semantics of Zend PHP define the semantics of PHP itself. Due to the complex and nuanced semantics of PHP, defined by how Zend works, it is difficult for competing implementations to offer complete compatibility.

PHP's single-request-per-script-execution model, and the fact the Zend Engine is an interpreter, lead to inefficiency. As a result, various products have been developed to help improve PHP performance. In order to speed up execution time and not have to compile the PHP source code every time the web page is accessed, PHP scripts can also be deployed in the PHP engine's internal format by using an opcode cache, which works by caching the compiled form of a PHP script (opcodes) in shared memory to avoid the overhead of parsing and compiling the code every time the script runs. An opcode cache, Zend Opcache, is built into PHP since version 5.5.<ref>Template:Cite web</ref> Another example of a widely used opcode cache is the Alternative PHP Cache (APC), which is available as a PECL extension.<ref>Template:Cite web</ref>

While Zend PHP is still the most popular implementation, several other implementations have been developed. Some of these are compilers or support JIT compilation, and hence offer performance benefits over Zend PHP at the expense of lacking full PHP compatibility. Alternative implementations include the following:

  • HipHop Virtual Machine (HHVM)Template:Snd developed at Facebook and available as open source, it converts PHP code into a high-level bytecode (commonly known as an intermediate language), which is then translated into x86-64 machine code dynamically at runtime by a just-in-time (JIT) compiler, resulting in up to 6× performance improvements.<ref>Template:Cite web</ref>
  • ParrotTemplate:Snd a virtual machine designed to run dynamic languages efficiently; Pipp transforms the PHP source code into the Parrot intermediate representation, which is then translated into the Parrot's bytecode and executed by the virtual machine.
  • PhalangerTemplate:Snd compiles PHP into Common Intermediate Language (CIL) bytecode
  • HipHopTemplate:Snd developed at Facebook and available as open source, it transforms the PHP scripts into C++ code and then compiles the resulting code, reducing the server load up to 50%. In early 2013, Facebook deprecated it in favor of HHVM due to multiple reasons, including deployment difficulties and lack of support for the whole PHP language, including the create_function() and eval() constructs.<ref>Template:Cite web</ref>

Licensing

PHP is free software released under the PHP License, which stipulates that:<ref>Template:Cite web</ref>

Template:Quote

This restriction on use of the name PHP makes the PHP License incompatible with the GNU General Public License (GPL), while the Zend License is incompatible due to an advertising clause similar to that of the original license of BSD.<ref>Template:Cite web</ref>

Template:AnchorDevelopment and community

PHP includes various free and open-source libraries in its source distribution, or uses them in resulting PHP binary builds. PHP is fundamentally an Internet-aware system with built-in modules for accessing File Transfer Protocol (FTP) servers and many database servers, including PostgreSQL, MySQL, Microsoft SQL Server and SQLite (which is an embedded database), LDAP servers, and others. Numerous functions familiar to C programmers, such as those in the stdio family, are available in standard PHP builds.<ref>Template:Cite web</ref>

PHP allows developers to write extensions in C to add functionality to the PHP language. PHP extensions can be compiled statically into PHP or loaded dynamically at runtime. Numerous extensions have been written to add support for the Windows API, process management on Unix-like operating systems, multibyte strings (Unicode), cURL, and several popular compression formats. Other PHP features made available through extensions include integration with IRC, dynamic generation of images and Adobe Flash content, PHP Data Objects (PDO) as an abstraction layer used for accessing databases,<ref>Template:Cite web</ref><ref>O'Reilly Networks - ONLamp</ref><ref>IBM DeveloperWorks</ref><ref>Template:Cite web</ref><ref>IBM Redbooks</ref><ref>php|architect</ref><ref>Info</ref> and even speech synthesis. Some of the language's core functions, such as those dealing with strings and arrays, are also implemented as extensions.<ref>Cross Reference: /PHP_5_4/ext/standard/</ref> The PHP Extension Community Library (PECL) project is a repository for extensions to the PHP language.<ref>Template:Cite web</ref>

Some other projects, such as Zephir, provide the ability for PHP extensions to be created in a high-level language and compiled into native PHP extensions. Such an approach, instead of writing PHP extensions directly in C, simplifies the development of extensions and reduces the time required for programming and testing.<ref>Template:Cite web</ref>

Zend Technologies provides a certification exam for programmers to become certified PHP developers.

Template:AnchorInstallation and configuration

There are two primary ways for adding support for PHP to a web serverTemplate:Snd as a native web server module, or as a CGI executable. PHP has a direct module interface called Server Application Programming Interface (SAPI), which is supported by many web servers including Apache HTTP Server, Microsoft IIS, Netscape (now defunct) and iPlanet. Some other web servers, such as OmniHTTPd, support the Internet Server Application Programming Interface (ISAPI), which is a Microsoft's web server module interface. If PHP has no module support for a web server, it can always be used as a Common Gateway Interface (CGI) or FastCGI processor; in that case, the web server is configured to use PHP's CGI executable to process all requests to PHP files.<ref name="installation">Template:Cite web</ref>

PHP-FPM (FastCGI Process Manager) is an alternative FastCGI implementation for PHP, bundled with the official PHP distribution since version 5.3.3.<ref>Template:Cite web</ref> When compared to the older FastCGI implementation, it contains some additional features, mostly useful for heavily loaded web servers.<ref>Template:Cite web</ref>

When using PHP for command-line scripting, a PHP command-line interface (CLI) executable is needed. PHP supports a CLI SAPI as of PHP 4.3.0.<ref>Template:Cite web</ref> The main focus of this SAPI is developing shell applications using PHP. There are quite a few differences between the CLI SAPI and other SAPIs, although they do share many of the same behaviors.<ref>Template:Cite web</ref>

PHP can also be used for writing desktop graphical user interface (GUI) applications, by using the PHP-GTK extension. PHP-GTK is not included in the official PHP distribution,<ref name="installation" /> and as an extension it can be used only with PHP versions 5.1.0 and newer. The most common way of installing PHP-GTK is compiling it from the source code.<ref>Template:Cite web</ref>

When PHP is installed and used in cloud environments, software development kits (SDKs) are provided for using cloud-specific features. For example:

Numerous configuration options are supported, affecting both core PHP features and extensions.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> Configuration file php.ini is searched for in different locations, depending on the way PHP is used.<ref>Template:Cite web</ref> The configuration file is split into various sections,<ref>Template:Cite web</ref> while some of the configuration options can be also set within the web server configuration.<ref>Template:Cite web</ref>

Use

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A broad overview of the LAMP software bundle, displayed here together with Squid.

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.<ref>Template:Cite web</ref> It can also be used for command-line scripting and client-side graphical 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.<ref name="foundations">Template:Cite web</ref>

PHP acts primarily as a filter,<ref>Template:WaybackTemplate:Failed verification</ref> 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 parser compiles input to produce bytecode for processing by the Zend Engine, giving improved performance over its interpreter predecessor.<ref>Template:Cite web</ref>

Originally designed to create dynamic web pages, PHP now focuses mainly on server-side scripting,<ref>Template:Cite web</ref> 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,<ref>Template:Cite web</ref> 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, and Zend Framework, offering features similar to other web application frameworks.

The LAMP architecture has become popular in the web industry as a way of deploying web applications.<ref>Template:Cite web</ref> 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.

Template:As of, over 20 million Internet domains had web services hosted on servers with PHP installed and mod_php was recorded as the most popular Apache HTTP Server module.<ref name="usage">Template:Cite web</ref> Template:As of, PHP was used as the server-side programming language on 75% of all websites whose server-side programming language was known<ref name="W3Techs usage statistics">Template:Cite web</ref> (Template:As of, the percentage had reached 82%<ref name="W3Techs usage statistics">Template:Cite web</ref>), and PHP was the most-used open source software within enterprises.<ref>Template:Cite web</ref> Web content management systems written in PHP include MediaWiki,<ref>Template:Cite web</ref> Joomla, eZ Publish, SilverStripe,<ref>Template:Cite web</ref> WordPress,<ref>Template:Cite web</ref> Drupal,<ref>Template:Cite web</ref> Moodle,<ref>Template:Cite web</ref> the user-facing portion of Facebook,<ref>Template:Cite web</ref> and Digg.<ref>Template:Cite web</ref>

For specific and more advanced usage scenarios, PHP offers a well defined and documented way for writing custom extensions in C or C++.<ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref> 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.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> 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.<ref>Template:Cite book</ref>

PHP received mixed reviews due to lacking support for multithreading at the core language level,<ref>Template:Cite web</ref> though using threads is made possible by the "pthreads" PECL extension.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

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In 2013, 9% of all vulnerabilities listed by the National Vulnerability Database were linked to PHP;<ref name="CVE">Template:Cite web</ref> historically, about 30% of all vulnerabilities listed since 1996 in this database are linked to PHP. Technical security flaws of the language itself or of its core libraries are not frequent (22 in 2009, about 1% of the total although PHP applies to about 20% of programs listed).<ref name="PHP-related vulnerabilities on the National Vulnerability Database">Template:Cite web</ref> Recognizing that programmers make mistakes, some languages include taint checking to automatically detect the lack of input validation which induces many issues. Such a feature is being developed for PHP,<ref>Template:Cite web</ref> but its inclusion into a release has been rejected several times in the past.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

There are advanced protection patches such as Suhosin and Hardening-Patch, especially designed for web hosting environments.<ref>Template:Cite web</ref>

There are certain language features and configuration parameters (primarily the default values for such runtime settings) that make PHP prone to security issues. Among these, magic_quotes_gpc and register_globals<ref name="register-globals">Template:Cite web</ref> configuration directives are the best known; the latter made any URL parameters become PHP variables, opening a path for serious security vulnerabilities by allowing an attacker to set the value of any uninitialized global variable and interfere with the execution of a PHP script. Support for "magic quotes" and "register globals" has been deprecated as of PHP 5.3.0, and removed as of PHP 5.4.0.<ref name="register-globals" /><ref>Template:Cite web</ref>

Another example for the runtime settings vulnerability comes from failing to disable PHP execution (via engine configuration directive)<ref>Template:Cite web</ref> for the directory where uploaded images are stored; leaving the default settings can result in execution of malicious PHP code embedded within the uploaded images.<ref>Template:Cite web</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref> Also, leaving enabled the dynamic loading of PHP extensions (via enable_dl configuration directive)<ref>Template:Cite web</ref> in a shared web hosting environment can lead to security issues.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

Also, implied type conversions that result in incompatible values being treated as identical against the programmer's intent can lead to security issues. For example, the result of 0e1234 == 0 comparison will be true because the first compared value will be treated as scientific notation of a number (Template:Val) with value of zero. This feature resulted in authentication vulnerabilities in Simple Machines Forum,<ref>Template:Cite web</ref> Typo3<ref>Template:Cite web</ref> and phpBB<ref>Template:Cite web</ref> when MD5 password hashes were compared. Instead, identity operator (===) should be used; 0e1234 === 0 results in false.<ref>Template:Cite web</ref>

See also

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References

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External links

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