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Zend Technologies, PHP Foundation
First appeared8 June 1995; 28 years ago (1995-06-08)[1][2]
Stable release
8.2.10 / 29 August 2023; 25 days ago (2023-08-29)[3]
Preview release
8.3.0 Beta 3 / 17 August 2023; 37 days ago (2023-08-17)[4]
Quercus, Parrot
Influenced by
Perl, C, C++, Java,[7] Tcl,[2] JavaScript[8]
Hack, JSP, ASP, React JS

PHP is a

recursive initialism PHP: Hypertext Preprocessor.[15]

PHP code is usually processed on a

HTTP response. Various web template systems, web content management systems, and web frameworks exist that can be employed to orchestrate or facilitate the generation of that response. Additionally, PHP can be used for many programming tasks outside the web context, such as standalone graphical applications[16] and robotic drone control.[17] PHP code can also be directly executed from the command line

The standard 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 a variety of operating systems and platforms.[18]

The PHP language evolved without a written formal specification or standard until 2014, with the original implementation acting as the de facto standard that other implementations aimed to follow. Since 2014, work has gone on to create a formal PHP specification.[19]

W3Techs reports that as of September 2023, "PHP is used by 77.0% of all the websites whose server-side programming language we know."[20] It also reports that only 16.7% of PHP users use the currently supported 8.x versions. Most by far use the unsupported PHP 7, more specifically PHP 7.4, while 20% use PHP 5 (slightly more than use the supported PHP 8.x), which is not supported with security fixes and is known to have serious security vulnerabilities. This most likely indicates that these websites are vulnerable, those using 5.x, while it not does not necessarily indicate that for those using 7.x, since Linux distributions such as Ubuntu and Debian provide commercial support, and it may provide security patches for some unsupported 7.x versions such as 7.4 of PHP.[21][22]


Rasmus Lerdorf, creator of PHP; and Andi Gutmans and Zeev Suraski, creators of the Zend Engine

Early history

PHP development began in 1993

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. To accelerate bug reporting and improve the code, Lerdorf initially announced the release of PHP/FI as "Personal Home Page Tools (PHP Tools) version 1.0" on the Usenet discussion group comp.infosystems.www.authoring.cgi on 8 June 1995.[1][25] This release already had the basic functionality that PHP has today. This included Perl-like variables, form handling, and the ability to embed HTML. The syntax resembled that of Perl, but was simpler,[citation needed] more limited[citation needed] and less consistent.[citation needed][12]

An example of the early PHP syntax:[26]

<!--include /text/header.html-->

<!--getenv HTTP_USER_AGENT-->
<!--if substr $exec_result Mozilla-->
  Hey, you are using Netscape!<p>

<!--sql database select * from table where user='$username'-->
<!--ifless $numentries 1-->
  Sorry, that record does not exist<p>
<!--endif exit-->
  Welcome <!--$user-->!<p>
  You have <!--$index:0--> credits left in your account.<p>

<!--include /text/footer.html-->

Early PHP was not intended to be a new

testing, officially released PHP/FI 2 in November 1997.

The fact that PHP was not originally designed, but instead was developed organically has led to inconsistent naming of functions and inconsistent ordering of their parameters.

hash values.[30]

PHP 3 and 4

This is an example of PHP code for the WordPress content management system.

Zend Technologies in Ramat Gan, Israel.[12]

On 22 May 2000, PHP 4, powered by the Zend Engine 1.0, was released.[12] By August 2008, this branch had reached version 4.4.9. PHP 4 is now no longer under development and nor are any security updates planned to be released.[33][34]


On 1 July 2004, PHP 5 was released, powered by the new Zend Engine II.

Late static binding had been missing from previous versions of PHP, and was added in version 5.3.[36][37]

Many high-profile open-source projects ceased to support PHP 4 in new code from February 5, 2008, because of the GoPHP5 initiative,[38] provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.[39][40]

Over time, PHP interpreters became available on most existing

64-bit operating systems, either by building them from the PHP source code or by using pre-built binaries.[41] For PHP versions 5.3 and 5.4, the only available Microsoft Windows binary distributions were 32-bit IA-32 builds,[42][43] 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.[44]

Official security support for PHP 5.6 ended on 31 December 2018.[45]

PHP 6 and Unicode

PHP received mixed reviews due to lacking native Unicode support at the core language level.[46][47] 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.[48] 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.[49]

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.[50] 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 to contain most remaining non-Unicode features from PHP 6, such as traits and closure re-binding.[51] Initial hopes were that a new plan would be formed for Unicode integration, but by 2014 none had been adopted.


During 2014 and 2015, a new major PHP version was developed, PHP 7. The numbering of this version involved some debate among internal developers.[52] While the PHP 6 Unicode experiments had never been released, several articles and book titles referenced the PHP 6 names, which might have caused confusion if a new release were to reuse the name.[53] After a vote, the name PHP 7 was chosen.[54]

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,[55] and aimed to optimize PHP performance by refactoring the Zend Engine while retaining near-complete language compatibility.[56] By 14 July 2014, WordPress-based benchmarks, which served as the main benchmark suite for the phpng project, showed an almost 100% increase in performance. Changes from phpng make it easier to improve performance in future versions, as more compact data structures and other changes are seen as better suited for a successful migration to a just-in-time (JIT) compiler.[57] Because of the significant changes, the reworked Zend Engine was called Zend Engine 3, succeeding Zend Engine 2 used in PHP 5.[58]

Because of the major internal changes in phpng, it must receive a new major version number of PHP, rather than a minor PHP 5 release, according to PHP's release process.[59] 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. In particular, it involved the following changes:

PHP 7 also included new language features. Most notably, it introduced return type declarations for functions[72] which complement the existing parameter type declarations, and support for the scalar types (integer, float, string, and boolean) in parameter and return type declarations.[73]


PHP 8 was released on 26 November 2020. PHP 8 is a major version and has breaking changes from previous versions.[74][75] New features and notable changes include:

Just-in-time compilation

Just-in-time compilation is supported in PHP 8.[76]

PHP 8's JIT compiler can provide substantial performance improvements for some use cases,[77][78] while PHP developer Nikita Popov stated that the performance improvements for most websites will be less substantial than the upgrade from PHP 5 to PHP 7.[79] Substantial improvements are expected more for mathematical-type operations than for common web-development use cases.[79] Additionally, the JIT compiler provides the future potential to move some code from C to PHP, due to the performance improvements for some use cases.[80]

Addition of the match expression

PHP 8 introduced the match expression.[81] The match expression is conceptually similar to a switch statement and is more compact for some use cases.[82] Because match is an expression, its result can be assigned to a variable or returned from a function.[83]

Type changes and additions

PHP 8 introduced union types, a new static return type, and a new mixed type.[74]

"Attributes", often referred to as "annotations" in other programming languages, were added in PHP 8, which allow metadata to be added to classes.[74]

throw was changed from being a statement to being an expression.[84] This allows exceptions to be thrown in places that were not previously possible.[74]

Syntax changes and additions

PHP 8 includes changes to allow alternate, more concise, or more consistent syntaxes in a number of scenarios. For example, the nullsafe operator is similar to the null coalescing operator ??, but used when calling methods.[85] The following code snippet will not throw an error if getBirthday() returns null:

$human_readable_date = $user->getBirthday()?->diffForHumans();

Constructor property promotion has been added as "syntactic sugar," allowing class properties to be set automatically when parameters are passed into a class constructor.[74] This reduces the amount of boilerplate code that must be written.

Other minor changes include support for use of ::class on objects, which serves as an alternative for the use of get_class();[74] non-capturing catches in try-catch blocks; variable syntax tweaks to resolve inconsistencies; support for named arguments; and support for trailing commas in parameter lists, which adds consistency with support for trailing commas in other contexts, such as in arrays.

Standard library changes and additions

  • Weak maps were added in PHP 8. A WeakMap holds references to objects, but these references do not prevent such objects from being garbage collected.[86] This can provide performance improvements in scenarios where data is being cached; this is of particular relevance for object relational mappings (ORM).[74]
  • Various adjustments to interfaces, such as adding support for creating DateTime objects from interfaces, and the addition of a Stringable interface that can be used for type hinting.
  • Various new functions including str_contains(), str_starts_with(), and str_ends_with();[87] fdiv(); get_debug_type(); and get_resource_id()
  • Object implementation of token_get_all()

Additional changes

  • Type annotations were also added into PHP's C source code itself to allow internal functions and methods to have "complete type information in reflection."[88]
  • Inheritance with private methods
  • Abstract methods in traits improvements

PHP 8.1

PHP 8.1 was released on 8 December 2021, and included a number of new features and improvements over previous versions. Here is a more detailed look at some of the key features and improvements in PHP 8.1:

  • Union types: This feature allows you to specify that a variable can have multiple types, such as an integer or a string. This can be useful for writing more flexible and robust code, as it allows you to handle a wider range of input values.
  • Nullsafe operator: This operator allows you to chain method calls without worrying about null references. For example, if you want to call a method on an object that may be null, you can use the null safe operator to ensure that the method is only called if the object is not null.
  • Match expression: This is a more concise and flexible way to perform matching on values. It allows you to specify multiple cases and their associated values, and then use the match keyword to select the appropriate case based on the value of an expression.
  • Improved performance: PHP 8.1 includes various performance improvements, such as faster array operations and better memory usage. These improvements can help make your code run faster and more efficiently.
  • New error handling features: PHP 8.1 introduces a new throws keyword that allows you to specify which exceptions a function can throw, and a new assert() function that can be used to check for certain conditions at runtime. These features can help you write more reliable and robust code.
  • Other new features: PHP 8.1 also includes other new features such as support for named arguments, support for attributes (similar to annotations in other languages), and improved support for Unicode.[89]

The match expression is a new feature in PHP 8.1 that allows you to perform value matching in a more concise and flexible way. It is similar to a switch statement, but with some additional features and syntax improvements.

Here is an example of how you can use the match expression in PHP:

$value = 3;

$result = match ($value) {
  0 => 'The value is zero',
  1, 2, 3 => 'The value is one, two, or three',
  default => 'The value is something else',

echo $result; // Outputs: "The value is one, two, or three"

In this example, the match expression compares the value of $value to the different cases specified in the curly braces. If $value matches one of the cases, the corresponding value is returned. If none of the cases matches, the default case is used.

One of the main benefits of the match expression is that it allows you to specify multiple values for a single case, as shown in the example above. This can help make your code more concise and easier to read.

Assert() Error handling

The assert() function and the throws keyword are new error-handling features in PHP 8.1 that can help you write more reliable and robust code.

The assert() function is used to check for certain conditions at runtime. If the condition is not met, the function generates an AssertionError exception. For example:

assert($x > 0, '$x must be greater than zero');

In this example, the assert() function checks whether $x is greater than zero. If it is not, an AssertionError exception is thrown with the message "$x must be greater than zero".

The throws keyword, on the other hand, is used to specify which exceptions a function or method can throw. This can be helpful for documenting your code and making it easier for other developers to understand how your functions and methods behave. For example:

function divide(int $a, int $b): int
    if ($b === 0) {
        throw new DivisionByZeroError('Cannot divide by zero');

    return $a / $b;

In this example, the divide() function uses the throws keyword to specify that it can throw a DivisionByZeroError exception if the second argument is zero.

Overall, the assert() function and the throws keyword are useful tools for handling errors and exceptions in PHP and can help you write more reliable and robust code.[90]

Support for enumerations

Support for enumerations was one of the most prominent features of PHP 8.1.[91] Enums allow developers to programmatically enforce states in their codebase. Below is an example of an enum:


namespace App\Enums;

enum InvoiceStatus: string {
    case draft = 'draft';
    case pending = 'pending';
    case paid = 'paid';
    case expired = 'expired';

Other PHP 8.1 features

  • Support for 'read-only' properties was added.
  • After the introduction of array unpacking in PHP 7.4 with consecutively numbered keys, PHP 8.1 introduced support for array unpacking with string keys.
  • PHP 8.1 added support for using 'new' in initializers.
  • A new syntax was added for creating callables.
  • PHP 8.1 brought support for Pure Intersection Types, after the introduction of union types in PHP 8.0.

PHP 8.2

PHP 8.2 includes a number of new features and improvements. Here are some of the main ones:

  1. Improved Type Variance: PHP 8.2 introduces improved type variance for generic types, allowing you to specify whether a generic type is covariant, contravariant, or invariant. This can help to improve type safety and flexibility when working with generic types.
  2. Performance Improvements: PHP 8.2 includes various performance improvements, including faster JIT compilation, faster garbage collection, and improved handling of large arrays. These improvements can help to make PHP applications faster and more efficient.
  3. Deprecations: Some features have been deprecated in PHP 8.2, including the assert() function when used with a string argument, and the list() construct with a single array element. It's important to be aware of these deprecations if you are upgrading from an earlier version of PHP.

Here are some examples of features that have been deprecated in PHP 8.2:

  1. assert() function with string argument: The assert() function can be used to perform runtime checks, but it has been deprecated when used with a string argument. Instead, you should use the assert() function with a boolean argument or an expression.
  2. list() construct with a single array element: The list() construct allows you to unpack the elements of an array into separate variables. It has been deprecated when used with a single array element, as this usage was considered confusing and error-prone.
  3. create_function(): The create_function() function has been deprecated, as it has been superseded by anonymous functions, which are more flexible and easier to use.
  4. mb_ereg_replace_callback(): The mb_ereg_replace_callback() function has been deprecated, as it has been superseded by the preg_replace_callback() function, which provides similar functionality and is more widely used.
  5. Callables that are not accepted by the $callable() syntax (but are accepted by call_user_func()) are deprecated.

New "Random" extension

The "Random" extension provides a new object-oriented API for generating random values in PHP. It includes several classes ("Engine"s) that implement different algorithms for generating random numbers and storing their state within objects. This allows for multiple independent seedable sequences, which can be useful in certain contexts, such as testing or simulation.

The \Random\Randomizer class provides a high-level interface for using the engine's randomness to generate a random integer, shuffle an array or string, select random array keys, and more. This can be a convenient way to perform these common tasks without having to directly use the lower-level engine classes.

It's worth noting that the "Random" extension is not enabled by default in PHP, and you will need to install and enable it in your PHP environment in order to use its features. You can find more information about the extension in the official PHP documentation.[92]

Release history

Version Release date Supported until[93] Notes
Old version, no longer maintained: 1.0 8 June 1995 Officially called "Personal Home Page Tools (PHP Tools)". This is the first use of the name "PHP".[12]
Old version, no longer maintained: 2.0 1 November 1997 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.
Old version, no longer maintained: 3.0 6 June 1998 20 October 2000[93] Development moves from one person to multiple developers. Zeev Suraski and Andi Gutmans rewritten the base for this version.[12]
Old version, no longer maintained: 4.0 22 May 2000[94] 23 June 2001[93] Added more advanced two-stage parse/execute tag-parsing system called the Zend engine.[95]
Old version, no longer maintained: 4.1 10 December 2001[96] 12 March 2002[93] Introduced "superglobals" ($_GET, $_POST, $_SESSION, etc.)[95]
Old version, no longer maintained: 4.2 22 April 2002[97] 6 September 2002[93] 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.[95]
Old version, no longer maintained: 4.3 27 December 2002[98] 31 March 2005[93] Introduced the command-line interface (CLI), to supplement the CGI.[95][99]
Old version, no longer maintained: 4.4 11 July 2005[100] 7 August 2008[93] Fixed a memory corruption bug, which required breaking binary compatibility with extensions compiled against PHP version 4.3.x.[101]
Old version, no longer maintained: 5.0 13 July 2004[102] 5 September 2005[93] Zend Engine II with a new object model.[103]
Old version, no longer maintained: 5.1 24 November 2005[104] 24 August 2006[93] Performance improvements with the introduction of compiler variables in re-engineered PHP Engine.[103] Added PHP Data Objects (PDO) as a consistent interface for accessing databases.[105]
Old version, no longer maintained: 5.2 2 November 2006[106] 6 January 2011[93] Enabled the filter extension by default. Native JSON support.[103]
Old version, no longer maintained: 5.3 30 June 2009[107] 14 August 2014[93] Namespace support; late static bindings, jump label (limited goto), anonymous functions, closures, PHP archives (phar), garbage collection for circular references, improved Windows support, sqlite3, mysqlnd as a replacement for libmysql as the 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.
Old version, no longer maintained: 5.4 1 March 2012[108] 3 September 2015[93] 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.[109] Several improvements to existing features, performance and reduced memory requirements.
Old version, no longer maintained: 5.5 20 June 2013[110] 10 July 2016[111] Support for generators, finally blocks for exceptions handling, OpCache (based on Zend Optimizer+) bundled in official distribution.[112]
Old version, no longer maintained: 5.6 28 August 2014[113] 31 December 2018[111] 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.[114]
6.x Not released Abandoned version of PHP that planned to include native Unicode support.[115][116]
Old version, no longer maintained: 7.0 3 December 2015[117] 10 January 2019[59] Zend Engine 3 (performance improvements
exceptions,[60] and shorthand syntax for importing multiple items from a namespace.[128]
Old version, no longer maintained: 7.1 1 December 2016 1 December 2019[111] iterable type,[129] nullable types,[130] void return type,[131] class constant visibility modifiers,[132] short list syntax,[133] multi-catch[134]
Old version, no longer maintained: 7.2 30 November 2017 30 November 2020[111] Object parameter and return type declaration,[135] Libsodium extension,[136] abstract method overriding,[137] parameter type widening[138]
Old version, no longer maintained: 7.3 6 December 2018[139] 6 December 2021 Flexible Heredoc and Nowdoc syntax,[140] support for reference assignment and array deconstruction with list(),[141] PCRE2 support,[142] hrtime() function[143]
Old version, no longer maintained: 7.4 28 November 2019[144] 28 November 2022 Typed properties 2.0,[145] preloading,[146] null-coalescing assignment operator,[147] improve openssl_random_pseudo_bytes,[148] Weak References,[86] FFI – foreign function interface,[149] always available hash extension,[150] password hash registry,[151] multibyte string splitting,[152] reflection for references,[153] unbundle ext/wddx,[154] new custom object serialization mechanism[155]
Older version, yet still maintained: 8.0 26 November 2020[156] 26 November 2023 Just-In-Time (JIT) compilation,[76] arrays starting with a negative index,[157] stricter/saner language semantics (validation for abstract trait methods),[158] saner string to number comparisons,[159] saner numeric strings,[160] TypeError on invalid arithmetic/bitwise operators,[161] reclassification of various engine errors,[162] consistent type errors for internal functions,[163] fatal error for incompatible method signatures[164]), locale-independent float to string conversion,[165] variable syntax tweaks,[166] attributes,[167][168][169][170] named arguments,[171] match expression,[172] constructor property promotion,[173] union types,[174] mixed type,[175] static return type,[176] nullsafe operator,[85] non-capturing catches,[177] throw expression,[84] JSON extension is always available.[178]
Older version, yet still maintained: 8.1 25 November 2021[179] 25 November 2024 Explicit octal integer literal notation,[180] enumerations,[181] readonly properties,[182] first-class callable syntax,[183] new in initializers,[184] pure intersection types,[185] never return type,[186] final class constraints,[187] fibers[188]
Current stable version: 8.2 8 December 2022[189] 8 December 2025 Readonly classes,[190] null, false, and true as stand-alone types,[191][192] locale-independent case conversion,[193] disjunctive normal form types,[194] constants in traits[195]
Future release: 8.3 23 November 2023[196] 23 November 2026
Old version
Older version, still maintained
Latest version
Latest preview version
Future release

Beginning on 28 June 2011, the PHP Development Team implemented a timeline for the release of new versions of PHP.[59] Under this system, at least one release should occur every month. Once per year, a minor release should occur which may include new features. Every minor release should at least be supported for two years with security and bug fixes, followed by at least one year of only security fixes, for a total of a three-year release process for every minor release. No new features, unless small and self-contained, are to be introduced into a minor release during the three-year release process.


The elePHPant, PHP mascot

The mascot of the PHP project is the elePHPant, a blue

plush toy

Many variations of this mascot have been made over the years. Only the elePHPants based on the original design by Vincent Pontier are considered official by the community.[200] These are collectable and some of them are extremely rare.[201]


A "Hello World" application in PHP 7.4 running on its built-in development server

The following "Hello, World!" program is written in PHP code embedded in an HTML document:

<!DOCTYPE html>
        <title>PHP "Hello, World!" program</title>
            echo '<p>Hello, World!</p>';

However, as no requirement exists for PHP code to be embedded in HTML, the simplest version of Hello, World! may be written like this, with the closing tag ?> omitted as preferred in files containing pure PHP code.[202]

<?php echo 'Hello, World!';

The PHP interpreter only executes PHP code within its

control structures described in PHP code. The most common delimiters are <?php to open and ?> to close PHP sections. The shortened form <? also exists. This short delimiter makes script files less portable since support for them can be disabled in the local PHP configuration and it is therefore discouraged.[203][204] Conversely, there is no recommendation against the echo short tag <?=.[205] 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.[206][207][203] The purpose of all these delimiters is to separate PHP code from non-PHP content, such as JavaScript code or HTML markup.[208] So the shortest "Hello, World!" program
written in PHP is:

<?='Hello, World!';

The first form of delimiters, <?php and ?>, in XHTML and other XML documents, creates correctly formed XML processing instructions.[209] This means that the resulting mixture of PHP code and other markups in the server-side file is itself well-formed XML.

Variables are

callback functions. However, before PHP 7, type declarations could not be used with scalar types such as integers or strings.[73]

Below is an example of how PHP variables are declared and initialized.

    $name = 'John';  // variable of string type being declared and initialized
    $age = 18;       // variable of integer type being declared and initialized
    $height = 5.3;   // variable of double type being declared and initialized
    echo $name . ' is ' . $height . "m tall\n"; // concatenating variables and strings
    echo "$name is $age years old."; // interpolating variables to string

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.[210] PHP treats newlines as whitespace in the manner of a free-form language, and statements are terminated by a semicolon.[211] PHP has three types of comment syntax: /* */ marks block and inline comments; // or # are used for one-line comments.[212]
The echo statement is one of several facilities PHP provides to output text.

In terms of keywords and language syntax, PHP is similar to 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 is

C-language long type. Unsigned integers are converted to signed values in certain situations, which is different behaviour to many other programming languages.[213] Integer variables can be assigned using decimal (positive and negative), octal, hexadecimal, and binary

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++.[214]

The null data type represents a variable that has no value; NULL is the only allowed value for this data type.[214]

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.[214]

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

heredoc syntax.[215]

The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes.[216]


PHP defines a large array of functions in the core language and many are also available in various extensions; these functions are well documented online PHP documentation.[217] However, the built-in library has a wide variety of naming conventions and associated inconsistencies, as described under history above.

Custom functions may be defined by the developer:

function myAge(int $birthYear): string
    // calculate the age by subtracting the birth year from the current year.
    $yearsOld = date('Y') - $birthYear;

    // return the age in a descriptive string.
    return $yearsOld . ($yearsOld == 1 ? ' year' : ' years');

echo 'I am currently ' . myAge(1995) . ' old.';

As of 2023, the output of the above sample program is "I am currently 28 years old."

In lieu of

functions called with the PHP operator new, in which case parentheses are optional.

Since PHP 4.0.1 create_function(), a thin wrapper around eval(), allowed normal PHP functions to be created during program execution; it was deprecated in PHP 7.2 and removed in PHP 8.0[219] in favor of syntax for anonymous functions or "closures"[220] that can capture variables from the surrounding scope, which was added in PHP 5.3. Shorthand arrow syntax was added in PHP 7.4:[221]

function getAdder($x) {
    return fn($y) => $x + $y;

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

In the example above, getAdder() function creates a closure using passed argument $x, 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.[222]

Unusually for a dynamically typed language, PHP supports type declarations on function parameters, which are enforced at runtime. This has been supported for classes and interfaces since PHP 5.0, for arrays since PHP 5.1, for "callables" since PHP 5.4, and scalar (integer, float, string and boolean) types since PHP 7.0.[73] PHP 7.0 also has type declarations for function return types, expressed by placing the type name after the list of parameters, preceded by a colon.[72] For example, the getAdder function from the earlier example could be annotated with types like so in PHP 7:

function getAdder(int $x): Closure
    return fn(int $y): int => $x + $y;

$adder = getAdder(8);
echo $adder(2); // prints "10"
echo $adder(null); // throws an exception because an incorrect type was passed
$adder = getAdder([]); // would also throw an exception

By default, scalar type declarations follow weak typing principles. So, for example, if a parameter's type is int, PHP would allow not only integers, but also convertible numeric strings, floats or booleans to be passed to that function, and would convert them.[73] However, PHP 7 has a "strict typing" mode which, when used, disallows such conversions for function calls and returns within a file.[73]

PHP objects


value types.[223] The drawback of this method was that code had to make heavy use of PHP's "reference" variables if it wanted to modify an object it was passed rather than creating a copy of it. In the new approach, objects are referenced by handle
, and not by value.

PHP 5 introduced private and protected

virtual table feature in the engine, so static variables are bound with a name instead of a reference at compile time.[224]

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.[225]


inherited classes (and to the class that defines the item). private limits visibility only to the class that defines the item.[226]
Objects of the same type have access to each other's private and protected members even though they are not the same instance.


The following is a basic example of object-oriented programming in PHP 8:


abstract class User
    protected string $name;

    public function __construct(string $name)
        // make first letter uppercase and the rest lowercase
        $this->name = ucfirst(strtolower($name));

    public function greet(): string
        return "Hello, my name is " . $this->name;

    abstract public function job(): string;

class Student extends User
    public function __construct(string $name, private string $course)

    public function job(): string
        return "I learn " . $this->course;

class Teacher extends User
    public function __construct(string $name, private array $teachingCourses)

    public function job(): string
        return "I teach " . implode(", ", $this->teachingCourses);

$students = [
    new Student("Alice", "Computer Science"),
    new Student("Bob", "Computer Science"),
    new Student("Charlie", "Business Studies"),

$teachers = [
    new Teacher("Dan", ["Computer Science", "Information Security"]),
    new Teacher("Erin", ["Computer Science", "3D Graphics Programming"]),
    new Teacher("Frankie", ["Online Marketing", "Business Studies", "E-commerce"]),

foreach ([$students, $teachers] as $users) {
    echo $users[0]::class . "s:\n";

    array_walk($users, function (User $user) {
        echo "{$user->greet()}, {$user->job()}\n";

This program outputs the following:

Hello, my name is Alice, I learn Computer Science
Hello, my name is Bob, I learn Computer Science
Hello, my name is Charlie, I learn Business Studies
Hello, my name is Dan, I teach Computer Science, Information Security
Hello, my name is Erin, I teach Computer Science, 3D Graphics Programming
Hello, my name is Frankie, I teach Online Marketing, Business Studies, E-commerce


The only complete PHP implementation is the original, known simply as PHP. It is the most widely used and is powered by the Zend Engine. To disambiguate it from other implementations, it is sometimes unofficially called "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.[227][228] 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. 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 that the Zend Engine is an interpreter, leads 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

PECL extension.[230]

While Zend PHP is still the most popular implementation, several other implementations have been developed. Some of these are

JIT compilation
, and hence offer performance benefits over Zend PHP at the expense of lacking full PHP compatibility. Alternative implementations include the following:

  • just-in-time (JIT) compiler, resulting in up to 6× performance improvements.[231] However, since version 7.2 Zend has outperformed HHVM,[232] and HHVM 3.24 is the last version to officially support PHP.[233]
    • HipHop – 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 favour 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.[234]
  • Parrot – a virtual machine designed to run dynamic languages efficiently; the cross-translator 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.
  • PeachPie – a second-generation compiler to .NET Common Intermediate Language (CIL) bytecode, built on the Roslyn platform; successor of Phalanger, sharing several architectural components
  • Phalanger – compiles PHP into .Net Common Intermediate Language bytecode; predecessor of PeachPie
  • Quercus – compiles PHP into Java bytecode


PHP is free software released under the PHP License, which stipulates that:[235]

Products derived from this software may not be called "PHP", nor may "PHP" appear in their name, without prior written permission from [email protected]. You may indicate that your software works in conjunction with PHP by saying "

for PHP" instead of calling it "PHP Foo" or "phpfoo".

This restriction on the use of "PHP" makes the PHP License incompatible with the

BSD license.[236]

Development and community

PHP includes various

stdio family, are available in standard PHP builds.[237]

PHP allows developers to write

PHP Extension Community Library (PECL) project is a repository for extensions to the PHP language.[246]

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.[247]

By December 2018 the PHP Group consisted of ten people:

Andrei Zmievski.[248]

PHP Certification based on PHP 7[249]
exam (and previously based on PHP 5.5) for programmers to become certified PHP developers.

PHP Foundation

On 26 November 2021, the JetBrains blog announced the creation of the PHP Foundation, which will sponsor the design and development of PHP.[250]

Installation and configuration

Example output of the phpinfo() function in PHP 7.1

There are two primary ways for adding support for PHP to a web server – 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 and iPlanet Web Server. Some other web servers, such as OmniHTTPd, support the Internet Server Application Programming Interface (ISAPI), which is 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.[251]

PHP-FPM (FastCGI Process Manager) is an alternative FastCGI implementation for PHP, bundled with the official PHP distribution since version 5.3.3.[252] When compared to the older FastCGI implementation, it contains some additional features, mostly useful for heavily loaded web servers.[253]

When using PHP for command-line scripting, a PHP

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 behaviours.[255]

PHP has a direct module interface called SAPI for different web servers;[256] in case of PHP 5 and Apache 2.0 on Windows, it is provided in form of a DLL file called php5apache2.dll,[257] which is a module that, among other functions, provides an interface between PHP and the web server, implemented in a form that the server understands. This form is what is known as a SAPI.

There are different kinds of SAPIs for various web server extensions. For example, in addition to those listed above, other SAPIs for the PHP language include the Common Gateway Interface and command-line interface.[256][258]

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,[251] 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 by compiling it from the source code.[259]

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.[262][263] Configuration file php.ini is searched for in different locations, depending on the way PHP is used.[264] The configuration file is split into various sections,[265] while some of the configuration options can be also set within the web server configuration.[266]


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

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.[18]

Dynamic web page: example of server-side scripting (PHP and MySQL)

Originally designed to create dynamic

Yii Framework, Phalcon and Laminas, offering features similar to other web frameworks


WAMP and MAMP, are also available for Windows and macOS
, with the first letter standing for the respective operating system. Although both PHP and Apache are provided as part of the macOS base install, users of these packages seek a simpler installation mechanism that can be more easily kept up to date.

For specific and more advanced usage scenarios, PHP offers a well-defined and documented way for writing custom extensions in C or C++.[271][272][273][274][275][276][277] 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.[278][279] 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.[280]

PHP received mixed reviews due to lacking support for

PECL extension.[282][283]

A command line interface, php-cli, and two ActiveX Windows Script Host scripting engines for PHP have been produced.

Popularity and usage statistics

PHP is used for


As of January 2013[update], PHP was used in more than 240 million websites (39% of those sampled) and was installed on 2.1 million web servers.[290]

As of March 2021, PHP was used as the server-side programming language on 79.1% of websites, down from 83.5% previously, where the language could be determined, and PHP 7 is the most used version of the language with 50.3% of all websites on the web using that version.[291]


In 2019, 11% of all vulnerabilities listed by the National Vulnerability Database were linked to PHP;[292] 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).[293] 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,[294] but its inclusion into a release has been rejected several times in the past.[295][296]

There are advanced protection patches such as Suhosin and Hardening-Patch, specially designed for web hosting environments.[297]

Historically, old versions of PHP had some configuration parameters and default values for such runtime settings that made some PHP applications prone to security issues. Among these, magic_quotes_gpc and register_globals[298] configuration directives were 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" settings has been deprecated since PHP 5.3.0, and removed from PHP 5.4.0.[299]

Another example for the potential runtime-settings vulnerability comes from failing to disable PHP execution (for example by using the engine configuration directive)[300] for the directory where uploaded files are stored; enabling it can result in the execution of malicious code embedded within the uploaded files.[301][302][303] The best practice is to either locate the image directory outside of the document root available to the web server and serve it via an intermediary script or disable PHP execution for the directory which stores the uploaded files.

Also, enabling the dynamic loading of PHP extensions (via enable_dl configuration directive)

shared web hosting environment can lead to security issues.[305][306]


strcmp or the identity operator (===), as '0e1234' === '0' results in false.[310]

In a 2013 analysis of over 170,000 website defacements, published by Zone-H, the most frequently (53%) used technique was the exploitation of file inclusion vulnerability, mostly related to insecure usage of the PHP language constructs include, require, and allow_url_fopen.[311][312]

As of April 2021, W3Techs reports that 64% of websites using PHP, use versions 7.2 or older (which are

no longer supported
by The PHP Development Team) with 35% of all PHP websites using version 5.6 or older.[313]

Version 5 is still used by 24.5% of all websites (September 2021).[314] It is highly recommended to migrate to PHP version 7 or 8 and use random_int() instead of rand() or mt_rand(), as the latter functions are not cryptographically-secure. There are two attacks that can be performed over PHP entropy sources: "seed attack" and "state recovery attack". With current[when?] GPU technologies, an attacker can perform up to 230 MD5 calculations per second with a $250 GPU, while with an additional $500 can reach up to 232 calculations.[315] In combination with a "birthday attack" this can lead to serious security vulnerabilities.

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