PHP (Hypertext Preprocessor): Web Development Explained

PHP, short for 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. It is a server-side scripting language designed for web development, but it is also used as a general-purpose programming language.

PHP code is executed on the server, and the result is returned to the browser as plain HTML. PHP files can contain text, HTML, CSS, JavaScript, and PHP code. PHP code is enclosed with special start and end processing instructions that allow you to jump into and out of "PHP mode".

History of PHP

PHP was originally created by Rasmus Lerdorf in 1994. The main implementation of PHP is now produced by The PHP Group and serves as the formal reference to the PHP language. PHP originally stood for Personal Home Page, but it now stands for the recursive initialism PHP: Hypertext Preprocessor.

Over the years, PHP has evolved from a simple scripting language for creating dynamic web pages into a robust language used for server-side scripting, command-line scripting, and coding applications. The PHP Group has released several versions of PHP, with PHP 7.4 being the latest stable version as of 2019.

PHP 3 and PHP 4

PHP 3, released in 1998, was a significant rewrite of PHP 2, and the base of PHP 3 was a complete rewrite of PHP 2, adding support for object-oriented programming, the syntax which is still used today. PHP 4, released in 2000, introduced the Zend Engine, a scripting engine that interprets PHP code and turns it into machine-readable code.

PHP 4 improved upon PHP 3 by offering more advanced features, better performance, and greater reliability. It also introduced "super globals" ($_GET, $_POST, $_SESSION, etc.) and offered enhanced support for a variety of databases.

PHP 5 and PHP 7

PHP 5, released in 2004, brought with it a host of improvements and features, such as improved support for object-oriented programming, the introduction of the Standard PHP Library (SPL), and enhancements to the MySQL extension with the introduction of MySQLi.

PHP 7, released in 2015, marked a significant improvement in performance, boasting speeds twice as fast as PHP 5.6. It also introduced new features such as return type declarations, scalar type hints, and the spaceship operator.

PHP Syntax

PHP scripts start with . A PHP file normally contains HTML tags, and some PHP scripting code. Like other programming languages, PHP has variables, operators, loops, conditionals, functions, and arrays.

PHP is a loosely typed language, which means that it automatically converts certain types of data from one type to another if necessary. For example, if you use a string (text) in a mathematical operation, PHP will automatically convert the string to a number.

Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable. PHP variables are case-sensitive, which means $age, $AGE, and $Age are considered three different variables.

PHP variables can hold different data types such as integers, floats (floating point numbers), strings (sequence of characters), arrays (indexed collection of data), objects (instances of classes), and NULL (a special data type that only has one value: NULL).

Operators

PHP has a wide range of operators that allow you to perform operations on variables. These include arithmetic operators, assignment operators, comparison operators, increment/decrement operators, logical operators, string operators, array operators, and conditional assignment operators.

For example, the '+' operator adds two numbers together, the '==' operator checks if two values are equal, and the '&&' operator returns true if both conditions are true.

PHP and HTML

PHP can be embedded directly into HTML code, or it can be used in combination with various web template systems, web content management systems, and web frameworks. PHP code is enclosed in special start and end processing instructions that allow you to jump into and out of "PHP mode".

When a PHP page is accessed, the PHP code is read or "parsed" by the server the page resides on. The PHP pre-processor then generates HTML output to be displayed on the viewer's browser screen.

Embedding PHP in HTML

Embedding PHP in HTML is as simple as enclosing your PHP code within the PHP start and end tags. The PHP code is executed on the server, and the HTML result is sent to the browser. The end user does not see the PHP code, but only the resulting HTML.

For example, you might have a PHP script that retrieves information from a database, and you want to display this information in an HTML table. You would embed the PHP code that retrieves the data within your HTML code that generates the table.

Using PHP with Web Template Systems

Web template systems, such as Smarty and Twig, allow you to separate your PHP code from your HTML code. This can make your code easier to manage, especially for large applications, and allows designers and developers to work on the same project without stepping on each other's toes.

With a web template system, you create HTML templates with placeholders for content. Your PHP scripts then fill in these placeholders with actual content, such as text from a database or user input.

PHP and Databases

PHP is often used to interact with databases. This allows you to store, retrieve, and manipulate data in a variety of ways. PHP supports a wide range of databases, including MySQL, PostgreSQL, SQLite, Oracle, and Microsoft SQL Server.

PHP provides several ways to interact with databases, including the MySQLi extension, the PDO (PHP Data Objects) extension, and the older, now deprecated, mysql extension.

Using PHP with MySQL

MySQL is the most commonly used database with PHP. PHP's MySQLi extension (MySQL Improved) provides a procedural and object-oriented interface to the MySQL database. It supports prepared statements, multiple statements, transactions, and more.

With PHP and MySQL, you can create dynamic web pages that actually interact with your users. For example, you can create a login page, a shopping cart, a content management system, a feedback form, and much more.

Using PHP with Other Databases

While MySQL is the most commonly used database with PHP, PHP is not limited to MySQL. PHP supports a wide range of databases, and with the PDO extension, you can access and manipulate data from a variety of databases using the same functions and methods.

The PDO extension defines a consistent interface for accessing databases in PHP. This means that, regardless of which database you're using, the functions to issue queries and fetch data will be the same.

PHP and Web Frameworks

PHP is often used in conjunction with web frameworks, which are collections of classes, libraries, and runtimes that help you build complex web applications more easily. Some popular PHP frameworks include Laravel, Symfony, CodeIgniter, and Zend Framework.

Using a PHP framework can help you develop applications faster and work better, because it abstracts many of the common tasks, such as routing, database abstraction, form processing, and more, that can be time-consuming to code from scratch.

Using PHP with Laravel

Laravel is a popular PHP framework that provides a clean and elegant syntax, and includes tools for tasks such as routing, authentication, sessions, caching, and unit testing. Laravel is built with a focus on writing code that is simple, readable, and well-documented.

With Laravel, you can build everything from small, simple web applications to large, complex systems. Laravel also includes a powerful ORM (Object-Relational Mapping) for working with your database. This ORM allows you to interact with your database using PHP syntax, rather than writing SQL queries.

Using PHP with Other Frameworks

While Laravel is a popular choice, there are many other PHP frameworks that might be a better fit for your project. Symfony is a set of reusable PHP components and a PHP framework for web projects. CodeIgniter is a powerful PHP framework with a very small footprint, built for developers who need a simple and elegant toolkit to create full-featured web applications.

Zend Framework is a collection of professional PHP packages with more than 570 million installations. It can be used to develop web applications and services using PHP 5.6+, and provides 100% object-oriented code using a broad spectrum of language features.

Conclusion

PHP is a powerful and flexible language that is widely used for web development. Whether you're building a small personal website or a large enterprise application, PHP has the features, frameworks, and resources to help you get the job done.

With a strong community, a wealth of tutorials and resources, and a robust ecosystem of frameworks and tools, PHP continues to be a popular choice for web developers around the world.