PHP/LAMP Developemt

PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.

PHP is a reflective programming language originally designed for producing dynamic web pages. PHP is used mainly in server-side scripting, but can be used from a command line interface or in standalone graphical applications. Textual User Interfaces can also be created using ncurses.

Usage

PHP generally runs on a web server, taking PHP code as its input and creating Web pages as output, however it can also be used for command-line scripting and client-side GUI applications. PHP can be deployed on most web servers and on almost every OS platform free of charge. The PHP Group also provides the complete source code for users to build, customize and extend for their own use.

Server-side Scripting

Originally designed to create dynamic web pages, PHP's principal focus is server-side scripting. While running the PHP parser with a web server and web browser, the PHP model can be compared to other server-side scripting languages such as Microsoft's ASP.NET system, Sun Microsystems' JavaServer Pages, mod_perl and the Ruby on Rails framework, as they all provide dynamic content to the client from a web server. To more directly compete with the "framework" approach taken by these systems, Zend is working on the Zend Framework - an emerging set of PHP building blocks and best practices; other PHP frameworks along the same lines include CakePHP, PRADO and Symfony.

The LAMP architecture has become popular in the Web industry as a way of deploying inexpensive, reliable, scalable, secure web applications. PHP is commonly used as the P in this bundle alongside Linux, Apache and MySQL. PHP can be used with a large number of relational database management systems, runs on all of the most popular web servers and is available for many different operating systems. This flexibility means that PHP has a wide installation base across the Internet; over 19 million Internet domains are currently hosted on servers with PHP installed.

Examples of popular server-side PHP applications include phpBB, WordPress, and MediaWiki.

Command-line Scripting

PHP also provides a command line interface SAPI for developing shell and desktop applications, daemons, log parsing, or other system administration tasks. PHP is increasingly used on the command line for tasks that have traditionally been the domain of Perl, Python, awk, or shell scripting.

Client-side GUI applications

PHP provides bindings to GUI libraries such as GTK+, with PHP-GTK, and text mode libraries like ncurses in order to facilitate development of a broader range of cross-platform GUI applications.

Data Types

PHP stores whole numbers in a platform-dependent range. This range is typically that of 32-bit signed integers. 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, named "boolean", similar to the native Boolean types in Java and C++. Using the Boolean type conversion rules, non-zero values can be interpreted as true and zero as false, as in Perl.

The null data type represents a variable that has no value. The only value in the null data type is NULL.

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.

Arrays support both numeric and string indices, and are heterogeneous. 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.

Objects

Basic Object-oriented programming functionality was added in PHP 3. However, handling of objects was completely rewritten for PHP 5, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types. The drawback of this method was that semantically 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 abstract methods. It also introduced a standard way of declaring constructors and destructors similar to that of other object-oriented languages, such as C++, and an exception handling model similar to that of other programming languages.

The static method and class variable features in Zend Engine 2 do not work the way some expect. There is no virtual table feature in the engine, so the static variables are bound with a name at compile time instead of with a reference.

If the developer asks to create a copy of an object by using the reserved word clone, the Zend engine will check if a __clone() method has been defined or not. If not, it will call a default __clone() which will copy all of the object's properties. If a __clone() method is defined, then it will be responsible to set the necessary properties in the created object. For convenience, the engine will supply a function that imports all of the properties from the source object, so that they can start with a by-value replica of the source object, and only override properties that need to be changed.

Resources

Libraries

PHP includes a large number of 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.

Extension

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, and dynamic generation of images and Adobe Flash content. The PHP Extension Community Library (PECL) project is a repository for extensions to the PHP language.

Source code Encoders, Optimizers and Accelerators

Encoders offer some source code security and enable proprietary software by hindering source code reverse engineering. Encoders fall broadly into two types; those that hide source code and those that compile code into bytecode. The downside of this latter approach is that a special extension has to be installed on the server in order to run encoded scripts, however the approach of encoding compiled code and use of an extension offers typically the best performance, security and opportunity for additional features that may be useful for developers. Compiled code solutions may exploit the potential for increased security through the use of their own execution engine, although some simpler solutions rely on the regular PHP engine to execute the compiled code. The most commonly used packages for source code protection are from Zend Technologies and ionCube Ltd.

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 many opportunities for code optimization.

Accelerators offer 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. Both commercial and open source accelerators are available.

Debuggers and Profilers

Debuggers and profilers allow developers to analyze running PHP code for potential and noted software bugs and bottlenecks. Examples of such software for PHP include APD and Xdebug.

Templating Engines

Templating engines provide macros that allow PHP applications to uniformly identify common variables. One popular templating engine is Smarty.

PEAR

The PHP Extension and Application Repository (PEAR) project aims to provide reusable libraries and components for PHP development. PEAR projects are usually written in PHP code using the Object-oriented programming paradigm.