PHP

Rasmus Lerdorf, who wrote the original Common Gateway Interface (CGI) component, together with Andi Gutmans and Zeev Suraski, who rewrote the parser that formed PHP 3.

PHP development began in 1994 when Rasmus Lerdorf wrote several Common Gateway Interface (CGI) programs in C,[16][17][18] 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.

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 June 8, 1995.[19][20] 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, more limited and less consistent.[7]

An example of the early PHP syntax:

<!--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-->

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."[21] A development team began to form and, after months of work and beta 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.[22] In some cases, the function names were chosen to match the lower-level libraries which PHP was "wrapping",[23] 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.[24]

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

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.[7][25] 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.[26] They also founded Zend Technologies in Ramat Gan, Israel.[7]

On May 22, 2000, PHP 4, powered by the Zend Engine 1.0, was released.[7] By August 2008 this branch reached version 4.4.9. PHP 4 is no longer under development nor will any security updates be released.[27][28]

On July 14 2004, PHP 5 was released powered by the new Zend Engine II.[7] 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.[29] 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.[30][31]

Many high-profile open-source projects ceased to support PHP 4 in new code from February 5, 2008, because of the GoPHP5 initiative,[32] provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.[33][34]

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.[35] For PHP versions 5.3 and 5.4, the only available Microsoft Windows binary distributions were 32-bit IA-32 builds,[36][37] 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.[38]

Official security support for PHP 5.6 ended on 31 December 2018.[39]

PHP received mixed reviews due to lacking native Unicode support at the core language level.[40][41] 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.[42] 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.[43]

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.[44] 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.[45] 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, which was numbered PHP 7. The numbering of this version involved some debate among internal developers.[46] While the PHP 6 Unicode experiment had never been released, several articles and book titles referenced the PHP 6 name, which might have caused confusion if a new release were to reuse the name.[47] After a vote, the name PHP 7 was chosen.[48]

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,[49] and aimed to optimize PHP performance by refactoring the Zend Engine while retaining near-complete language compatibility.[50] 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 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.[51] Because of the significant changes, the reworked Zend Engine is called Zend Engine 3, succeeding Zend Engine 2 used in PHP 5.[52]

Because of 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.[53] 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:

• Many fatal- or recoverable-level legacy PHP error mechanisms were replaced with modern object-oriented exceptions.[54]
• 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.[55]
• Support for legacy PHP 4-style constructor methods was deprecated.[56]
• The behavior of the foreach statement was changed to be more predictable.[57]
• Constructors for the few classes built-in to PHP which returned null upon failure were changed to throw an exception instead, for consistency.[58]
• Several unmaintained or deprecated server application programming interfaces (SAPIs) and extensions were removed from the PHP core, most notably the legacy mysql extension.[59]
• The behavior of the list() operator was changed to remove support for strings.[60]
• Support was removed for legacy ASP-style delimiters <% and %> and <script language="php"> ... </script>.[61]
• An oversight allowing a switch statement to have multiple default clauses was fixed.[62]
• Support for hexadecimal number support in some implicit conversions from strings to number types was removed.[63]
• The left-shift and right-shift operators were changed to behave more consistently across platforms.[64]
• Conversions between floating-point numbers and integers were changed (e.g. infinity changed to convert to zero) and implemented more consistently across platforms.[64][65]

PHP 7 also included new language features. Most notably, it introduces return type declarations for functions[66] which complement the existing parameter type declarations, and support for the scalar types (integer, float, string, and boolean) in parameter and return type declarations.[67]

PHP 8 was released on November 26, 2020. PHP 8 is a major version and has breaking changes from previous versions.[68][69] New features and notable changes include:

Just-in-time compilation is supported in PHP 8.[70]

PHP 8's JIT compiler can provide substantial performance improvements for some use cases.[71][72] PHP developer Nikita Popov has stated that the performance improvements for most websites will be less substantial than the upgrade from PHP 5 to PHP 7.[73] Performance improvements due to the addition of the JIT compiler are expected to be more substantial for mathematical-type operations than for common web-development use cases.[73] Additionally, the JIT compiler provides future potential to move some code from C to PHP, due to the performance improvements for some use cases.[74]

PHP 8 introduced the match expression.[75] The match expression is conceptually similar to a switch statement and is more compact for some use cases.[76] Because match is an expression, its result can be caught into a variable or returned from a function.[77]

PHP 8 introduced union types, a new static return type, and a new mixed type.[68]

"Attributes", often referred to as "annotations" in other programming languages, were added in PHP 8, which allow metadata to be added to classes.[68]

throw was changed from being a statement to being an expression.[78] This allows exceptions to be thrown in places that were not previously possible.[68]

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.[79] 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.[68] 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();[68] 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.

• 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.[80] This can provide performance improvements in scenarios where data is being cached; this is of particular relevance for ORMs.[68]
• 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();[81] fdiv(); get_debug_type(); and get_resource_id()
• Object implementation of token_get_all()

• 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."[82]
• Inheritance with private methods
• Abstract methods in traits improvements

Beginning on June 28, 2011, the PHP Development Team implemented a timeline for the release of new versions of PHP.[53] 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.

PHP is a loosely coupled language, since it does not depend on the data type. This is the one of the main features of the language. 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 behavior to many other programming languages.[181] 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.[182] 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++.[182]

The null data type represents a variable that has no value; NULL is the only allowed value for this data type.[182]

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.[182]

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.[182] PHP also supports strings, which can be used with single quotes, double quotes, nowdoc or heredoc syntax.[183]

The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes.[184]

PHP defines a large array of functions in the core language and many are also available in various extensions; these functions are well documented in the online PHP documentation.[185] 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 $yearsOld . ' year' . ($yearsOld != 1 ? 's':'');
}

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

In 2021, the output of the above sample program is 'I am currently 26 years old.'

In lieu of function pointers, functions in PHP can be referenced by a string containing their name. In this manner, normal PHP functions can be used, for example, as callbacks or within function tables.[186] User-defined functions may be created at any time without being prototyped.[185][186] Functions may be defined inside code blocks, permitting a run-time decision as to whether or not a function should be defined. There is a function_exists function that determines whether a function with a given name has already been defined. Function calls must use parentheses, with the exception of zero-argument class constructor functions called with the PHP operator new, in which case parentheses are optional.

Until PHP 5.3, support for anonymous functions and closures did not exist in PHP. While create_function() has existed since PHP 4.0.1, it is merely a thin wrapper around eval() that allows normal PHP functions to be created during program execution.[187] PHP 5.3 added syntax to define an anonymous function or "closure"[188] which can capture variables from the surrounding scope. Shorthand arrow syntax was added in PHP 7.4:[189]

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 (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.[190]

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.[67] 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.[66] 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.[67] However, PHP 7 has a "strict typing" mode which, when used, disallows such conversions for function calls and returns within a file.[67]

Basic object-oriented programming functionality was added in PHP 3 and improved in PHP 4.[7] This allowed for PHP to gain further abstraction, making creative tasks easier for programmers using the language. Object handling was completely rewritten for PHP 5, expanding the feature set and enhancing performance.[191] In previous versions of PHP, objects were handled like value types.[191] 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 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.[192]

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.[193]

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.[194] 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:

<?php

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 $course)
    {
        parent::__construct($name);
    }

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

class Teacher extends User
{
    public function __construct(string $name, private array $teachingCourses)
    {
        parent::__construct($name);
    }

    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"]),
];

function show(User ...$users): void
{
    echo $users[0]::class . "s: \n";

    foreach ($users as $user) {
        echo "{$user->greet()}, {$user->job()}\n";
    }
}

show(...$students);
show(...$teachers);

// Output of program:
// Students:
// 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
// Teachers:
// 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

PHP is used for Web content management systems including MediaWiki,[251] WordPress,[252] Joomla,[253] Drupal,[254] Moodle,[255] eZ Publish, eZ Platform, and SilverStripe.[256]

Websites using PHP include Facebook,[257] Digg,[258] Dailymotion,[259] Tumblr,[260].

As of January 2013, PHP was used in more than 240 million websites (39% of those sampled) and was installed on 2.1 million web servers.[261]

As of August 2019, PHP was used as the server-side programming language on 78.8% of websites, down from 83.5% previously, where the language could be determined.[262]

As of April 2020, PHP 7 is the most used version of the language[263] with 50.6% of sites using PHP and 39.6% of all websites on the web.[264]