PHP

Paradigm	Multi-paradigm: imperative, functional, object-oriented, procedural, reflective
Designed by	Rasmus Lerdorf
Developer	The PHP Development Team, Zend Technologies, PHP Foundation
First appeared	8 June 1995; 29 years ago (1995-06-08)[1][2]
Stable release	8.3.8 / 6 June 2024; 19 days ago (2024-06-06)[3]
Typing discipline	Dynamic, weak, gradual[4]
Implementation language	C (primarily; some components C++)
OS	Unix-like, Windows, macOS, IBM i, OpenVMS, IBM Z
License	dual licensed GNU General Public License version 2 or any later version and PHP License for PHP versions 3.0 or earlier.[5] Only PHP License (most of Zend engine under Zend Engine License) for 3.01x and later versions.
Filename extensions	.php,.phar,.phtml,.pht,.phps
Website	www.php.net
Major implementations
Zend Engine, HHVM, PeachPie, Quercus, Parrot
Influenced by
Perl, C, C++, Java,[6] Tcl,[2] JavaScript[7]
Influenced
Hack, JSP, ASP, React JS
PHP Programming at Wikibooks

PHP is a general-purpose scripting language geared towards web development.^[8] It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995.^[9][10] The PHP reference implementation is now produced by the PHP Group.^[11] PHP was originally an abbreviation of Personal Home Page,^[12][13] but it now stands for the recursive initialism PHP: Hypertext Preprocessor.^[14]

PHP code is usually processed on a web server by a PHP interpreter implemented as a module, a daemon or a Common Gateway Interface (CGI) executable. On a web server, the result of the interpreted and executed PHP code—which may be any type of data, such as generated HTML or binary image data—would form the whole or part of an 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^[15] and drone control.^[16] 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.^[17]

The PHP language has evolved without a written formal specification or standard, with the original implementation acting as the de facto standard that other implementations aimed to follow.

W3Techs reports that as of 23 May 2024^[update] (the six months after the PHP 8.3 release), PHP is used by 76.2% of all websites whose programming language could be determined, and 55.1% thereof use PHP 7 which is outdated and known to be insecure.^[18][19]

History

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

Early history

PHP development began in 1993^[9] when Rasmus Lerdorf wrote several Common Gateway Interface (CGI) programs in C,^[20][21] which he used to maintain his personal homepage. He extended them to work with web forms and to communicate with databases, and called this implementation "Personal Home Page/Forms Interpreter" or PHP/FI.

An example of the early PHP syntax:^[22]

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

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

<!--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-->

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][23] This release included basic functionality such as Perl-like variables, form handling, and the ability to embed HTML. By this point, the syntax had changed to resemble that of Perl, but was simpler, more limited, and less consistent.^[12][11]

Early PHP was never intended to be a new programming language; rather, it 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."^[24] A development team began to form and, after months of work and beta testing, officially released PHP/FI 2 in November 1997.^[25]

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.^[26] In some cases, the function names were chosen to match the lower-level libraries which PHP was "wrapping",^[27] 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.^[28]

PHP 3 and 4

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.^[11][29] 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.^[30] They also founded Zend Technologies in Ramat Gan, Israel.^[11]

On 22 May 2000, PHP 4, powered by the Zend Engine 1.0, was released.^[11] 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.^[31][32]

PHP 5

On 1 July 2004, PHP 5 was released, powered by the new Zend Engine II.^[11] 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.^[33] In 2008, PHP 5 became the only stable version under development. Late static binding had been missing from previous versions of PHP, and was added in version 5.3.^[34][35]

Many high-profile open-source projects ceased to support PHP 4 in new code from February 5, 2008, because of the GoPHP5 initiative,^[36] provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.^[37][38]

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.^[39] For PHP versions 5.3 and 5.4, the only available Microsoft Windows binary distributions were 32-bit IA-32 builds,^[40][41] 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.^[42]

Official security support for PHP 5.6 ended on 31 December 2018.^[43]

PHP 6 and Unicode

PHP received mixed reviews due to lacking native Unicode support at the core language level.^[44][45] 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.^[46] 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.^[47]

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.^[48] 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.^[49] Initial hopes were that a new plan would be formed for Unicode integration, but by 2014 none had been adopted.^{[citation needed]}

PHP 7

During 2014 and 2015, a new major PHP version was developed, PHP 7. The numbering of this version involved some debate among internal developers.^[50] 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.^[51] After a vote, the name PHP 7 was chosen.^[52]

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,^[53] and aimed to optimize PHP performance by refactoring the Zend Engine while retaining near-complete language compatibility.^[54] 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.^[55] Because of the significant changes, the reworked Zend Engine was called Zend Engine 3, succeeding Zend Engine 2 used in PHP 5.^[56]

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.^[57] 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.^{[citation needed]} In particular, it involved the following changes:

• Many fatal or recoverable-level legacy PHP error mechanisms were replaced with modern object-oriented exceptions.^[58]
• The syntax for variable dereferencing was reworked to be internally more consistent and complete, allowing the use of the operators ->, , (),{}, and ::, with arbitrary meaningful left-side expressions.^[59]
• Support for legacy PHP 4-style constructor methods was deprecated.^[60]
• The behavior of the foreach statement was changed to be more predictable.^[61]
• Constructors for the few classes built-in to PHP which returned null upon failure were changed to throw an exception instead, for consistency.^[62]
• Several unmaintained or deprecated server application programming interfaces (SAPIs) and extensions were removed from the PHP core, most notably the legacy mysql extension.^[63]
• The behavior of the list() operator was changed to remove support for strings.^[64]
• Support was removed for legacy ASP-style delimiters <% and %> and <script language="php"> ... </script>.^[65]
• An oversight allowing a switch statement to have multiple default clauses was fixed.^[66]
• Support for hexadecimal number support in some implicit conversions from strings to number types was removed.^[67]
• The left-shift and right-shift operators were changed to behave more consistently across platforms.^[68]
• Conversions between floating-point numbers and integers were changed (e.g. infinity changed to convert to zero) and implemented more consistently across platforms.^[68][69]

PHP 7 also included new language features. Most notably, it introduced return type declarations for functions^[70] which complement the existing parameter type declarations, and support for the scalar types (integer, float, string, and boolean) in parameter and return type declarations.^[71]

PHP 8

PHP 8 was released on 26 November 2020, and is currently the second-most used PHP major version. PHP 8 is a major version and has breaking changes from previous versions.^[72][73] New features and notable changes include:

Just-in-time compilation

Just-in-time compilation is supported in PHP 8.^[74]

PHP 8's JIT compiler can provide substantial performance improvements for some use cases,^[75][76] 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.^[77] Substantial improvements are expected more for mathematical-type operations than for common web-development use cases.^[77] 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.^[78]

Addition of the match expression

PHP 8 introduced the match expression.^[79] The match expression is conceptually similar to a switch statement and is more compact for some use cases.^[80] Because match is an expression, its result can be assigned to a variable or returned from a function.^[81]

Type changes and additions

PHP 8 introduced union types, a new static return type, and a new mixed type.^[72]

"Attributes", often referred to as "annotations" in other programming languages, were added in PHP 8, which allow metadata to be added to classes.^[72]

throw was changed from being a statement to being an expression.^[82] This allows exceptions to be thrown in places that were not previously possible.^[72]

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.^[83] 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.^[72] This reduces the amount of boilerplate code that must be written.^[84]

Other minor changes include support for use of ::class on objects, which serves as an alternative for the use of get_class();^[72] 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.^[73]

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.^[85] This can provide performance improvements in scenarios where data is being cached; this is of particular relevance for object–relational mappings (ORM).^[72]
• 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.^[72]
• Various new functions including str_contains(), str_starts_with(), and str_ends_with();^[86] fdiv(); get_debug_type(); and get_resource_id()^[72]
• Object implementation of token_get_all()^[72]

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."^[87]
• Inheritance with private methods^[72]
• Abstract methods in traits improvements^[72]

PHP 8.1

PHP 8.1 was released on November 25, 2021.^[88] It added support for enumerations (also called "enums"), declaring properties as readonly (which prevents modification of the property after initialization), and array unpacking with string keys. The new never type can be used to indicate that a function does not return.^[89]

PHP 8.2

PHP 8.2 was released on December 8, 2022.^[90] New in this release are readonly classes (whose instance properties are implicitly readonly), disjunctive normal form (DNF) types, and the random extension, which provides a pseudorandom number generator with an object-oriented API.^[91]

Release history

Beginning on 28 June 2011, the PHP Development Team implemented a timeline for the release of new versions of PHP.^[57] 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.

Mascot

The mascot of the PHP project is the elePHPant, a blue elephant with the PHP logo on its side, designed by Vincent Pontier^[203] in 1998.^[204] "The (PHP) letters were forming the shape of an elephant if viewed in a sideways angle."^[205] The elePHPant is sometimes differently coloured when in plush toy form.^[206]

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.^[207] These are collectable and some of them are extremely rare.^[208]

Syntax

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

<!DOCTYPE html>
<html>
    <head>
        <title>PHP "Hello, World!" program</title>
    </head>
    <body>
        <p><?= 'Hello, World!' ?></p>
    </body>
</html>

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.^[209]

<?php echo 'Hello, World!';

The PHP interpreter only executes PHP code within its delimiters. Anything outside of its delimiters is not processed by PHP, although the 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. 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.^[210][211] Conversely, there is no recommendation against the echo short tag <?=.^[212] 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.^{[213][214][210]} The purpose of all these delimiters is to separate PHP code from non-PHP content, such as JavaScript code or HTML markup.^[215] 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.^[216] This means that the resulting mixture of PHP code and other markups in the server-side file is itself well-formed XML.

Variables are prefixed with a dollar symbol, and a type does not need to be specified in advance. PHP 5 introduced type declarations that allow functions to force their parameters to be objects of a specific class, arrays, interfaces or callback functions. However, before PHP 7, type declarations could not be used with scalar types such as integers or strings.^[71]

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

<?php
    $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.^[217] PHP treats newlines as whitespace in the manner of a free-form language, and statements are terminated by a semicolon.^[218] PHP has three types of comment syntax: /* */ marks block and inline comments; // or # are used for one-line comments.^[219] The echo statement is one of several facilities PHP provides to output text.^{[citation needed]}

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.^{[citation needed]}

Data types

PHP is loosely typed. It stores integers in a platform-dependent range, either as a 32, 64 or 128-bit signed integer equivalent to the C-language long type. Unsigned integers are converted to signed values in certain situations, which is different behaviour to many other programming languages.^[220] Integer variables can be assigned using decimal (positive and negative), octal, hexadecimal, and binary notations.^{[citation needed]}

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.^[221] 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++.^[221]

The null data type represents a variable that has no value; NULL is the only allowed value for this data type.^[221]

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.^[221]

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.^[221] PHP also supports strings, which can be used with single quotes, double quotes, nowdoc or heredoc syntax.^[222]

The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes.^[223]

Functionsedit

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.^[224] 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.
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