What is PHP?
What can PHP do?
PHP (recursive acronym for "PHP: Hypertext Preprocessor") is a widely-used Open Source general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
Simple answer, but what does that mean? An example:
Example 1-1. An introductory example
<html>
<head>
<title>Example</title>
</head>
<body>
<?php
echo "Hi, I'm a PHP script!";
?>
</body>
</html>
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Notice how this is different from a script written in other languages like Perl or C -- instead of writing a program with lots of commands to output HTML, you write an HTML script with some embedded code to do something (in this case, output some text). The PHP code is enclosed in special start and end tags that allow you to jump into and out of "PHP mode".
What distinguishes PHP from something like client-side JavaScript is that the code is executed on the server. If you were to have a script similar to the above on your server, the client would receive the results of running that script, with no way of determining what the underlying code may be. You can even configure your web server to process all your HTML files with PHP, and then there's really no way that users can tell what you have up your sleeve.
The best things in using PHP are that it is extremely simple for a newcomer, but offers many advanced features for a professional programmer. Don't be afraid reading the long list of PHP's features. You can jump in, in a short time, and start writing simple scripts in a few hours.
Although PHP's development is focused on server-side scripting, you can do much more with it.
Read on, Detail see the about PHP Manual for more information.
Anything. PHP is mainly focused on server-side scripting, so you can do anything any other CGI program can do, such as collect form data, generate dynamic page content, or send and receive cookies. But PHP can do much more.
There are three main fields where PHP scripts are used.
- Server-side scripting. This is the most traditional and main target field for PHP. You need three things to make this work. The PHP parser (CGI or server module), a webserver and a web browser. You need to run the webserver, with a connected PHP installation. You can access the PHP program output with a web browser, viewing the PHP page through the server.
- Command line scripting. You can make a PHP script to run it without any server or browser. You only need the PHP parser to use it this way. This type of usage is ideal for scripts regularly executed using cron (on *nix or Linux) or Task Scheduler (on Windows). These scripts can also be used for simple text processing tasks.
- Writing client-side GUI applications. PHP is probably not the very best language to write windowing applications, but if you know PHP very well, and would like to use some advanced PHP features in your client-side applications you can also use PHP-GTK to write such programs. You also have the ability to write cross-platform applications this way. PHP-GTK is an extension to PHP, not available in the main distribution.
PHP can be used on all major operating systems, including Linux, many Unix variants (including HP-UX, Solaris and OpenBSD), Microsoft Windows, Mac OS X, RISC OS, and probably others. PHP has also support for most of the web servers today. This includes Apache, Microsoft Internet Information Server, Personal Web Server, Netscape and iPlanet servers, Oreilly Website Pro server, Caudium, Xitami, OmniHTTPd, and many others. For the majority of the servers PHP has a module, for the others supporting the CGI standard, PHP can work as a CGI processor.
So with PHP, you have the freedom of choosing an operating system and a web server. Furthermore, you also have the choice of using procedural programming or object oriented programming, or a mixture of them. Although not every standard OOP feature is realized in the current version of PHP, many code libraries and large applications (including the PEAR library) are written only using OOP code.
With PHP you are not limited to output HTML. PHP's abilities includes outputting images, PDF files and even Flash movies (using libswf and Ming) generated on the fly. You can also output easily any text, such as XHTML and any other XML file. PHP can autogenerate these files, and save them in the file system, instead of printing it out, forming a server-side cache for your dynamic content.
One of the strongest and most significant feature in PHP is its support for a wide range of databases. Writing a database-enabled web page is incredibly simple. The following databases are currently supported:
| Adabas D | Ingres | Oracle (OCI7 and OCI8) |
| dBase | InterBase | Ovrimos |
| Empress | FrontBase | PostgreSQL |
| FilePro (read-only) | mSQL | Solid |
| Hyperwave | Direct MS-SQL | Sybase |
| IBM DB2 | MySQL | Velocis |
| Informix | ODBC | Unix dbm |
We also have a DBX database abstraction extension allowing you to transparently use any database supported by that extension. Additionally PHP supports ODBC, the Open Database Connection standard, so you can connect to any other database supporting this world standard.
PHP also has support for talking to other services using protocols such as LDAP, IMAP, SNMP, NNTP, POP3, HTTP, COM (on Windows) and countless others. You can also open raw network sockets and interact using any other protocol. PHP has support for the WDDX complex data exchange between virtually all Web programming languages. Talking about interconnection, PHP has support for instantiation of Java objects and using them transparently as PHP objects. You can also use our CORBA extension to access remote objects.
PHP has extremely useful text processing features, from the POSIX Extended or Perl regular expressions to parsing XML documents. For parsing and accessing XML documents, we support the SAX and DOM standards. You can use our XSLT extension to transform XML documents.
While using PHP in the ecommerce field, you'll find the Cybercash payment, CyberMUT, VeriSign Payflow Pro and CCVS functions useful for your online payment programs.
Read on, Detail see the about PHP Manual for more information.
PHP/FI
PHP succeeds an older product, named PHP/FI. PHP/FI was created by Rasmus Lerdorf in 1995, initially as a simple set of Perl scripts for tracking accesses to his online resume. He named this set of scripts 'Personal Home Page Tools'. As more functionality was required, Rasmus wrote a much larger C implementation, which was able to communicate with databases, and enabled users to develop simple dynamic Web applications. Rasmus chose to release the source code for PHP/FI for everybody to see, so that anybody can use it, as well as fix bugs in it and improve the code.
PHP/FI, which stood for Personal Home Page / Forms Interpreter, included some of the basic functionality of PHP as we know it today. It had Perl-like variables, automatic interpretation of form variables and HTML embedded syntax. The syntax itself was similar to that of Perl, albeit much more limited, simple, and somewhat inconsistent.
By 1997, PHP/FI 2.0, the second write-up of the C implementation, had a cult of several thousand users around the world (estimated), with approximately 50,000 domains reporting as having it installed, accounting for about 1% of the domains on the Internet. While there were several people contributing bits of code to this project, it was still at large a one-man project.
PHP/FI 2.0 was officially released only in November 1997, after spending most of its life in beta releases. It was shortly afterwards succeeded by the first alphas of PHP 3.0.
PHP 3
PHP 3.0 was the first version that closely resembles PHP as we know it today. It was created by Andi Gutmans and Zeev Suraski in 1997 as a complete rewrite, after they found PHP/FI 2.0 severely underpowered for developing their own eCommerce application. In an effort to cooperate and start building upon PHP/FI's existing user-base, Andi, Rasmus and Zeev decided to cooperate and announce PHP 3.0 as the official successor of PHP/FI 2.0, and development of PHP/FI 2.0 was mostly halted.
One of the biggest strengths of PHP 3.0 was its strong extensibility features. In addition to providing end users with a solid infrastructure for lots of different databases, protocols and APIs, PHP 3.0's extensibility features attracted dozens of developers to join in and submit new extension modules. Arguably, this was the key to PHP 3.0's tremendous success. Other key features introduced in PHP 3.0 were the object oriented syntax support and the much more powerful and consistent language syntax.
The whole new language was released under a new name, that removed the implication of limited personal use that the PHP/FI 2.0 name held. It was named plain 'PHP', with the meaning being a recursive acronym - PHP: Hypertext Preprocessor.
By the end of 1998, PHP grew to an install base of tens of thousands of users (estimated) and hundreds of thousands of Web sites reporting it installed. At its peak, PHP 3.0 was installed on approximately 10% of the Web servers on the Internet.
PHP 3.0 was officially released in June 1998, after having spent about 9 months in public testing.
PHP 4
By the winter of 1998, shortly after PHP 3.0 was officially released, Andi Gutmans and Zeev Suraski had begun working on a rewrite of PHP's core. The design goals were to improve performance of complex applications, and improve the modularity of PHP's code base. Such applications were made possible by PHP 3.0's new features and support for a wide variety of third party databases and APIs, but PHP 3.0 was not designed to handle such complex applications efficiently.
The new engine, dubbed 'Zend Engine' (comprised of their first names, Zeev and Andi), met these design goals successfully, and was first introduced in mid 1999. PHP 4.0, based on this engine, and coupled with a wide range of additional new features, was officially released in May 2000, almost two years after its predecessor, PHP 3.0. In addition to the highly improved performance of this version, PHP 4.0 included other key features such as support for many more Web servers, HTTP sessions, output buffering, more secure ways of handling user input and several new language constructs.
PHP 4 is currently the latest released version of PHP. Work has already begun on modifying and improving the Zend Engine to integrate the features which were designed for PHP 5.0.
Today, PHP is being used by hundreds of thousands of developers (estimated), and several million sites report as having it installed, which accounts for over 20% of the domains on the Internet.
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