اموزش برنامه نویسی php

Evolution of PHP
Rasmus Lerdorf developed PHP in the year 1994. He incorporated this unreleased version of PHP into his home page. He used this version to monitor the number of users who accessed his online resume. No one knew about the existence of PHP until early 1995, when the first version of PHP was released. It was then known as Personal Home Page Tools

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Personal Home Page: PHP’s First Released Version
When PHP was first released for developers in early 1995, it was known as Personal Home Page Tools. This version of PHP comprised a parser engine that supported a few special macros and some utilities that were commonly used in home pages. This made PHP a popular choice among developers for creating and enhancing their home pages. PHP allowed developers to add some common functionality, such as guest books and counters, to their Web pages.

Note A parser is a program that breaks the source code into an object code. A parser is usually a part of the compiler and it receives input in the form of source program code, markup tags, or online commands. The parser breaks this input to yield objects and methods. These objects and methods can then be managed by other components of the compiler. A compiler is a program that converts programming language into machine language.

PHP/FI: PHP’s Second Version
In mid-1995, Rasmus wrote the parser again and renamed it PHP/FI Version 2. The FI in PHP/FI stands for Form Interpreter. This FI was a part of the package developed by Rasmus that could interpret HTML form data. However, PHP/FI did not contain only the Personal Home Page tools scripts and FI. In addition, it included support for mySQL. Thus, the combination of Personal Home Page tools scripts, Form Interpreter, and mSQL resulted in the second version of PHP, or PHP/FI.

Because of its powerful features and built-in database support, PHP/FI did not take long to get noticed, and soon people started working on it to find ways to improve it and add more functionality to it. Such was the popularity of PHP/FI that people even started to contribute their code to it. The rise in popularity of PHP/FI can be gauged from the fact that in late 1996 an estimated 15,000 Web sites used PHP/FI and by mid-1997 this number had swelled to more than 50,000 Web sites.

After PHP/FI came PHP 3, with more powerful and enhanced features.

PHP 3: PHP’s Third Version
Until mid-1997, PHP was limited to only a few people who had contributed their code to it-and, of course, to Rasmus, who had conceived it. However, given the speed with which PHP/FI gained recognition and popularity, it soon became the effort of a much bigger, well-coordinated, and systematic team. The parser was completely rewritten from scratch. This new parser, written by Zeev Suraski and Andi Gutmans, formed the very core of the third version of PHP, known as PHP 3. PHP 3 contained a considerable number of new features, and within no time people started using it for developing Web applications.

The combination of PHP 3, Apache, and MySQL soon became an instant hit and was considered the choice for developing Web pages. In addition to improved performance and other features, one more factor that made this combination an ideal one was that all three technologies were open-source technologies and were freely available. Thus, the problems of obtaining licenses and other hassles were completely eliminated.

Although Apache and MySQL are considered ideal and are the preferred software for use with PHP, this does not mean that PHP is not compatible with other software. It provides an equal degree of support to a variety of Web servers, such as Microsoft Internet Information Server (IIS), Personal Web Server (PWS), iPlanet servers, Oreilly Website Pro server, and Caudium. PHP provides support to a large number of databases. In fact, PHP’s support for such a large number of databases is one of its strongest and most significant features. The databases supported by PHP include Adabas, Oracle, Ingres, interBase, FrontBase, Empress, Ovrimos, PostgreSQL, FilePro (read-only), mSQL, Solid, Hyperwave, Direct MS-SQL, Sybase, IBM DB2, Unix dbm, Informix, and Velocis.

The latest version of PHP is PHP 4. This version was introduced in a more complex environment where Web development was not just about writing hard-coded HTML pages. Web applications were needed to be dynamic and interactive, and to provide support for database interactivity. Web applications were developed in such a manner that multiple users could send and retrieve data at the same time. In addition, the time to retrieve data or even load a page was also under consideration. According to a survey based on traditional human factors guidelines, 10 seconds is the maximum response time that the users can wait patiently for a Web page to load; beyond this they tend to lose interest. In addition, if even a single JavaScript error is detected on a Web page, a user is most likely to leave the Web page immediately.

Now you will learn about PHP 4 in detail.

PHP 4: The Latest Version
PHP 4, the latest version of PHP, has a lot of new features that allow it to deliver higher performance and to provide support to an ever-larger range of extensions and libraries. PHP 4 is fast becoming a de facto industry standard for developing Web pages. According to a recent survey conducted by Security Space (www.securityspace.com), PHP has emerged as the most popular and widely used scripting language. In October 2001, there were an estimated 1,107,914 PHP users as against 328,856 Perl users, 473,053 Open SSL users, and 1,873 mod_python users. Some of the most common and yet important factors that contributed to the success and rise of PHP are:

PHP 4 is available for free download from PHP’s official Web site. In addition, most software that is used with PHP, such as Apache and MySQL, is also available free of cost.

PHP is an open-source software. When I say that PHP is open-source software, I do not want to imply that there is any lack of support available for developers who choose PHP for Web development. The advice of several developers who have tried and tested applications using PHP is available free of cost on the Internet.

A lot of PHP support documents are available free of cost on the Internet.

Given the enormous number of users who are using PHP, there are numerous mailing lists that you can join. You can then post your problems or take part in discussion forums to solve the problems you are facing.

There is a dedicated team of volunteer experts who immediately rectify any bugs that are reported or detected in PHP. These experts are the people who are involved with the development of PHP language. They are not affiliated with any organization. If you encounter any bugs in PHP, you can report these bugs at the official site of PHP, www.php.net/. This site provides you with all the help you’ll need for reporting a bug and contacting the experts.

In terms of its performance, you can compare PHP with Active Server Pages (ASP). PHP is popular on Linux platforms, as ASP is popular on Windows. However, cross-platform support provided by PHP makes it score over ASP. PHP can be used as effectively on Windows platforms as on any other platform.

Unlike many other scripting languages, such as ASP, PHP comes with a built-in compiler that compiles PHP code and can detect errors in it. You can rectify the mistakes in your PHP code based on the mistakes pointed out by the compiler. No such compiler that compiles ASP code is available with ASP.

Another significant feature of PHP is its portability. PHP is compatible with any combination of software, and this is what makes it portable. It can work with almost any combination of operating system, Web server, and database server.

Now that you’re familiar with the success factors of PHP, it’s time to review the new and advanced features that have been added in PHP 4.

Support for Boolean datatype.

Support for Java and XML.

Support for COM/DCOM. This support is available only for Windows.

Support for FTP.

The ‘= = =’ operator. In addition to checking whether or not the two values are equal, this operator also checks whether the datatypes of these values are the same or not.

The ability to call a function even before it is declared. This is accomplished by using the runtime binding of functions in PHP 4.

The PHP highlighter. This feature enables you to view the source code instead of the complete script. This feature helps you to have a faster and better look at the source code.

Support for variable assignment by reference. This helps you to link two variables so that the value of one variable is dependent on the value of the other variable. Thus, the value of the variable is updated automatically whenever a value is assigned to another variable.

Server API (SAPI). This feature further enhances the support for Web servers.

Support for many algorithms, namely Triple DES, MD5, Blowfish, and SHA1. Through the mcrypt library, PHP 4 supports full encryption.

The ability to reference variables in PHP 4 by using quotes. Additionally, variable expansion is supported using double quotes.

Additional improvements to PHP 4 include:

In PHP 4, all syntax limitations that existed in PHP 3 have been overcome.

GET, POST methods in PHP 4 support multi-dimensional arrays.

In PHP 4, the php.ini file is simple to understand and configure.

In PHP 4, better ways of creating classes and objects have been introduced