PHP

Key takeaways

PHP belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PHP to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PHP from memory before moving on to harder problems.

Reference excerpt

PHP is a general-purpose scripting language geared towards web development. It was created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by the PHP Group. PHP was originally an abbreviation of Personal Home Page, but it now stands for the recursive backronym PHP: Hypertext Preprocessor. 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—can 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. PHP can be used for programming tasks outside the web context, though non-web uses are rare. 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.

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

Early history (1993 to 1997) PHP development began in 1993 when Rasmus Lerdorf wrote several Common Gateway Interface (CGI) programs in C, which he used to maintain his personal homepage. He extended them to work with HTML 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:

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. 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. 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." 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. In some cases, the function names were chosen to match the lower-level libraries which PHP was "wrapping", 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.

PHP 3 and 4 (1998 to 2004)

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. 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. They also founded Zend Technologies in Ramat Gan, Israel. On 22 May 2000, PHP 4.0, powered by the Zend Engine 1.0, was released. By August 2008, this branch had reached version 4.4.9. PHP 4 is now no longer under development nor are any security updates planned to be released.

Early PHP 5 (2004 to 2006) On 1 July 2004, PHP 5.0 was released, powered by the new Zend Engine 2.0. PHP 5.0 included significant changes to the language, most notably an overhauled approach to object-oriented programming, as well as iterators and exceptions. PHP 5.1 and PHP 5.2 were released the following years, adding smaller improvements and new features, such as the PHP Data Objects (PDO) extension (which defines a lightweight and consistent interface for accessing databases) In 2008, PHP 5.x became the only stable version under development. Many high-profile open-source projects ceased to support PHP 4 in new code from February 5, 2008, because of the GoPHP5 initiative, provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.

PHP 6 and Unicode PHP's native string functions worked only on raw bytes, making use with multibyte character encodings difficult. 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. 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. 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. As a result, a PHP 5.3 release was created in 2009, and 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. Initial hopes were that a new plan would be formed for Unicode integration, but by 2014 none had been adopted.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with PHP

Start with the simplest possible case. Write down what PHP claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PHP before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PHP ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PHP

In research: PHP appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses PHP in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: PHP is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1995 software, Class-based programming languages, Cross-platform software, so understanding it makes those chapters shorter.
In everyday life: Look for PHP outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study PHP in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PHP means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain PHP out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PHP in simple terms?

PHP is a general-purpose scripting language geared towards web development. It was created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995.

Why does PHP matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PHP?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PHP.