PHP Totally Explained

Everything about Php totally explained

| latest_test_version = 5.3.0-dev and 6.0-dev | license = PHP License | logo = | operating_system = Cross-platform | paradigm = imperative, object-oriented | typing = Dynamic, weak | year = 1995 | website = http://php.net/ }} PHP (a recursive acronym for PHP: Hypertext Preprocessor) is a computer scripting language, originally designed for producing dynamic web pages. It is for server-side scripting, but can be used from a command line interface or in standalone graphical applications.
   While PHP was originally created by Rasmus Lerdorf in 1995, the main implementation of PHP is now produced by The PHP Group and serves as the de facto standard for PHP as there's no formal specification.
   PHP is a widely-used general-purpose scripting language that's especially suited for web development and can be embedded into HTML. It generally runs on a web server, taking PHP code as its input and creating web pages as output. It can be deployed on most web servers and on almost every operating system and platform free of charge. It is also the most popular Apache module among computers using Apache as a web server. This release was named PHP version 2 and already had the basic functionality that PHP has today. This included Perl-like variables, form handling, and the ability to embed HTML. The syntax was similar to Perl but was more limited, simpler, and less consistent. The development team officially released PHP/FI 2 in November 1997 after months of beta testing. 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, which manages the development of PHP. The most recent update released by The PHP Group is for the older PHP version 4 code branch. As of January 2008, this branch is up to version 4.4.8. PHP 4 is no longer under active development but will be supported by security updates until August 8 2008.
   In 2008, PHP 5 became the only stable version under development. Late static binding has been missing from PHP and will be added in version 5.3. Alongside PHP 5, PHP 6 is also under active development. Major changes include the removal of register_globals, magic quotes, and safe mode.
   PHP doesn't have complete native support for Unicode or multibyte strings; unicode support will be included in PHP 6. Many high profile open source projects ceased to support PHP 4 in new code as of February 5 2008, due to the GoPHP5 initiative, provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.
   It runs in both 32-bit and 64-bit environments, but on Windows the only official distribution is 32-bit, requiring Windows 32-bit compatibility mode to be enabled while using IIS in a 64-bit Windows environment. There is a third-party distribution available for 64-bit Windows.

Release history

	Meaning
Red	Old release; not supported
Yellow	Old release; still supported
Green	Current release
Blue	Future release

Major Version	Minor Version	Release date	Notes
1.0	1.0.0	1995-06-08	Officially called "Personal Home Page Tools (PHP Tools)". This is the first use of the name "PHP".
4.1.0	2001-12-10	Introduced 'superglobals' (`$_GET`, `$_POST`, `$_SESSION`, etc.)
5.0	5.0.0	2004-07-13	Zend Engine II with a new object model.
	5.1.0	2005-11-24	Performance improvements with introduction of compiler variables in re-engineered PHP Engine.	Several security enhancements and bug fixes
	5.3.0	No date set	Namespace support; Improved XML support through use of XMLReader and XMLWriter; SOAP support
	6.0	6.0.0	No date set	Unicode support; removal of 'ereg', 'register_globals', 'magic_quotes' and 'safe_mode'; Alternative PHP Cache; Removal of mime_magic and rewrite of fileinfo for better MIME support

Usage

PHP is a general-purpose scripting language that's especially suited for web development. It is the fourth most popular computer programming language, ranking behind Java, C, and Visual Basic. PHP generally runs on a web server, taking PHP code as its input and creating web pages as output. It can also be used for command-line scripting and client-side GUI applications. PHP can be deployed on most web servers, many operating systems and platforms, and can be used with many relational database management systems. 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.
   PHP primarily acts as a filter, taking input from a file or stream containing text and/or PHP instructions and outputs another stream of data; most commonly the output will be HTML. It can automatically detect the language of the user. From PHP 4, the PHP parser compiles input to produce bytecode for processing by the Zend Engine, giving improved performance over its interpreter predecessor.
   Originally designed to create dynamic web pages, PHP's principal focus is server-side scripting, and it's similar to other server-side scripting languages that provide dynamic content from a web server to a client, such as Microsoft's ASP.NET system, Sun Microsystems' JavaServer Pages, and mod_perl. PHP has also attracted the development of many frameworks that provide building blocks and a design structure to promote rapid application development (RAD). Some of these include CakePHP, PRADO, Symfony and Zend Framework, offering features similar to other web application frameworks.
   The LAMP architecture has become popular in the web industry as a way of deploying web applications. PHP is commonly used as the P in this bundle alongside Linux, Apache and MySQL, although the P may also refer to Python or Perl.
   As of April 2007, over 20 million Internet domains were hosted on servers with PHP installed, and PHP was recorded as the most popular Apache module.

Security

PHP is a popular target of hackers who exploit poorly built applications written in PHP. Software vulnerabilities related to PHP are identified among the CVE (Common Vulnerabilities and Exposures) records, available from the National Vulnerability Database. The proportion of vulnerabilities related to PHP, out of the total of all common vulnerabilities, amounted to: 12% in 2003, 20% in 2004, 28% in 2005, 43% in 2006, 36% in 2007, and 33.8% for the first quarter of 2008. More than a quarter of all software vulnerabilities listed in this database are related to PHP, and more than a third of vulnerabilities listed recently. Most of these vulnerabilities can be exploited remotely, that's without being logged on the computer hosting the vulnerable application. Such exploitation is made possible due to poor programming habits, such as failing to check data before entering it into a database, and features of the language such as register_globals, which is now deprecated. These result in code injection, cross-site scripting and other application security issues. Such attacks are not exclusive to PHP and most can be avoided simply by following proper coding techniques and principles.

Syntax

PHP only parses code within its delimiters. Anything outside its delimiters is sent directly to the output and isn't parsed by PHP. The most common delimiters are

 and ?>, which are open and close delimiters respectively.  delimiters are also available. Short tags ( or  and ?>) are also commonly used, but like ASP-style tags (<% or <%= and %>), they're less portable as they can be disabled in the PHP configuration. For this reason, the use of short tags and ASP-style tags is discouraged. The purpose of these delimiters is to separate PHP code from non-PHP code, including HTML. Everything outside the delimiters is ignored by the parser and is passed through as output.

   Variables are prefixed with a dollar symbol and a type doesn't need to be specified in advance. Unlike function and class names, variable names are case sensitive. Both double-quoted ("") and heredoc strings allow the ability to embed the variable's value into the string. PHP treats newlines as whitespace in the manner of a free-form language (except when inside string quotes), and statements are terminated by a semicolon. PHP has three types of comment syntax: /* */ serves as block comments, and // as well as # are used for inline comments. To output text to the browser, either the print function or the echo function is used. Both functions are nearly identical; the major difference is that print is slower than echo because the former will return the integer value of 1 in order to behave more like a function, rather than a language construct, whereas the latter doesn't return a status and only returns the text for output.
Data types
PHP stores whole numbers in a platform-dependent range. This range is typically that of 32-bit signed integers. Unsigned integers are converted to signed values in certain situations; this behavior is different from other programming languages. Integer variables can be assigned using decimal (positive and negative), octal, and hexadecimal notations. Real numbers are also stored in a platform-specific range. They can be specified using floating point notation, or two forms of scientific notation. PHP has a native Boolean type that's 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++.
Functions
PHP has hundreds of base functions and thousands more from extensions. Functions are not first-class functions and can only be referenced by their name.
 User-defined functions can be created at any time without being prototyped. The drawback of this method was that the whole object was copied when a variable was assigned or passed as a parameter to a method. 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 and final classes as well as 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.

   If the developer creates a copy of an object using the reserved word clone, the Zend engine will check if a 
clone method is defined, then it'll 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 that the programmer can start with a by-value  of the source object and only override properties that need to be changed.
Resources
PHP includes free and open source libraries with the core build. PHP is a fundamentally Internet-aware system with modules built in for accessing FTP servers, many database servers, embedded SQL libraries such as embedded MySQL and SQLite, LDAP servers, and others. Many functions familiar to C programmers such as those in the stdio family are available in the standard PHP build. PHP has traditionally used features such as "magic_quotes_gpc" and "magic_quotes_runtime" which attempt to escape apostrophes (') and quotes (") in strings in the assumption that that'll be used in databases, to prevent SQL injection attacks. This leads to confusion over which data is escaped and which is not, and to problems when data isn't in fact used as input to a database and when the escaping used isn't completely correct. To make code portable between servers which do and don't use magic quotes, developers can preface their code with a script to reverse the effect of magic quotes when it's applied.

   PHP allows developers to write extensions in C to add functionality to the PHP language. These can then be compiled into PHP or loaded dynamically at runtime. Extensions have been written to add support for the Windows API, process management on Unix-like operating systems, multibyte strings (Unicode), cURL, and several popular compression formats. Some more unusual features include integration with Internet relay chat, dynamic generation of images and Adobe Flash content, and even speech synthesis. The PHP Extension Community Library (PECL) project is a repository for extensions to the PHP language.

   As with many scripting languages, PHP scripts are normally kept as human-readable source code, even on production web servers. While this allows flexibility, releasing scripts in source form is undesirable for commercial software developers, and can raise issues with security of web servers; as an example, if a hacker acquires control of a server, database passwords may be quickly discovered, and undesirable changes to scripts may be made that remain undiscovered indefinitely. Various encoding tools are available for PHP to offer code protection.

Code optimizers improve the quality of the compiled code by reducing its size and making changes that can reduce the execution time and improve performance. The nature of the PHP compiler is such that there are often opportunities for code optimization, and an example of a code optimizer is the Zend Optimizer PHP extension.

PHP accelerators can offer significant performance gains by caching the compiled form of a PHP script in shared memory to avoid the overhead of parsing and compiling the code every time the script runs. They may also perform code optimization to provide increased execution performance.


 Certification 
Zend provides a certification program for programmers to become certified PHP developers.

	
Further Information


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