PHP (originally used to mean “Personal Home Page Tools”) is a scripting language with a syntax similar to C and Perl, which is mainly used to create dynamic web pages or web applications. PHP is distributed as free software under the PHP license. PHP is characterized by broad database support and Internet Protocol integration, as well as the availability of numerous function libraries.
PHP in its original form is designed as a web-centric scripting language for web document templates. The widespread use of the Apache web server and the matching PHP extension module enables a cost-effective and low-threshold provision of web application environments on which software can be delivered as simple source code files quickly and easily via standard protocols such as SFTP. In addition, the step-by-step expansion of static web documents (HTML) with small auxiliary functions and manageable logic blocks makes it easy to get started with server-side web programming. Since the use of PHP as a template engine in this form is stateless and is often limited to manageable procedures, programming in PHP in many situations also eliminates more difficult, in-depth computer science problems, such as memory and process management or the need for callback functions. These features are also one of the reasons for the widespread use and popularity of PHP.
Also read Advantages of PHP (Over Other Web Programming Languages).
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How PHP Works
PHP is a system that processes PHP code on the server side. This means that the source code is not transmitted to the web browser, but to an interpreter on the web server. Only the output of the PHP interpreter is sent to the browser. In most cases, this is an HTML document, but it is also possible to generate other file types, such as images or PDF files, with PHP.
To be able to run a PHP file as part of a web application, you need a system that can handle the instructions contained in the file. For this reason, an interface, such as ISAPI or CGI, executes the interpreter from a server daemon or server service, such as Apache or IIS. The combination of Linux/Windows/macOS as the operating system, Apache as the web server, MySQL as the database system and PHP is called LAMP (for Linux), WAMP (for Windows) or MAMP (for Mac OS X). Ready-to-use LAMP, MAMP and WAMP packages, which eliminate the need to load and configure packages from the Internet individually, are being developed in the XAMPP project, for example. There are versions for Linux, Solaris, Windows and Mac OS X, but they are only intended to be used for test and development environments.
Since PHP usually runs in a web server environment, it is also subject to stateless HTTP. Every PHP page loads the web server with the interpreter, and the interpreter also processes the source code again every time it is called. This reduces the response speed of the server and increases the load. To counteract this, various bytecode caches are available that cache a version of the program prepared for execution and thus speed up access to this file the next time it is called (see also section Bytecode Caching and article PHP accelerator).
PHP can also be used to write command-line oriented scripts that are independent of the Internet. The Qt extension and the GTK extension even provide an application programming interface for a graphical user interface that does not require a web server or browser. The first versions of the interfaces to the graphical user interface and other operating system functions were sparse and hardly used. The currently developed PHP GTK version 2, on the other hand, aims to achieve 95% coverage of the GTK API. Currently, however, PHP is primarily used on web servers.
So, before diving into PHP coding, you need to set up a development environment. You can install PHP on your local machine using packages like XAMPP, WAMP, or MAMP, which include PHP, Apache, MySQL, and other necessary components for web development.
Examples of Basic Syntax and Structure
In PHP, three different types of comments are possible.
1 2 3 4 5 6 | // first comment # second comment /* long comment */ |
PHP code is embedded within HTML, typically enclosed within tags. Let’s start with a simple “Hello, World!” example:
1 2 3 | <?php echo "Hello, World!"; ?> |
In this example, the echo statement is used to output the string “Hello, World!” to the web page.
Variables and Data Types
Variables are used to store data that can be referenced and manipulated throughout your PHP scripts. PHP supports various data types, including integers, floats, strings, booleans, arrays, and objects. Variable names must begin with the dollar sign. Variables cannot be declared in PHP. The evaluation of a variable that has not yet been assigned a value gives a default value; a typo in the variable name is not an error in PHP.
Here’s an example demonstrating variable declaration and usage:
1 2 3 4 5 6 7 8 9 10 11 | <?php $name = "John"; $age = 30; $isMale = true; $height = 6.1; echo "Name: $name<br>"; echo "Age: $age<br>"; echo "Male: $isMale<br>"; echo "Height: $height feet"; ?> |
Constants must be declared in PHP. They are created using global or in classes using locally. Since PHP 7.1, class constants can also have visibility (without explicit specification, they are automatic, as in previous versions of PHP). It is common practice to write constant names in capital letters, but this is not required by the language.
1 2 | define('THIS_NAME', 'name'); ... |
Control Structures
PHP provides several control structures for executing code conditionally or repeatedly. Let’s explore some common ones:
If-Else Statement
1 2 3 4 5 6 7 8 9 | <?php $age = 25; if ($age >= 18) { echo "You are an adult."; } else { echo "You are a minor."; } ?> |
Loops: For, While, and Foreach
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | <?php // For Loop for ($i = 1; $i <= 5; $i++) { echo "Number: $i<br>"; } // While Loop $i = 1; while ($i <= 5) { echo "Number: $i<br>"; $i++; } // Foreach Loop (for arrays) $colors = array("Red", "Green", "Blue"); foreach ($colors as $color) { echo "Color: $color<br>"; } ?> |
Functions
Functions allow you to encapsulate reusable blocks of code. You can define your functions and call them wherever needed. Here’s an example of a simple function:
1 2 3 4 5 6 7 | <?php function greet($name) { echo "Hello, $name!"; } greet("Alice"); ?> |
Working with Forms
PHP is commonly used to process form data submitted by users. Let’s create a simple HTML form that submits data to a PHP script:
1 2 3 4 5 6 7 8 9 10 11 12 13 | <!DOCTYPE html> <html> <head> <title>Form Example</title> </head> <body> <form method="post" action="process.php"> Name: <input type="text" name="name"><br> Email: <input type="email" name="email"><br> <input type="submit" value="Submit"> </form> </body> </html> |
And here’s a PHP script (process.php) to handle form submission:
1 2 3 4 5 6 7 8 9 | <?php if ($_SERVER["REQUEST_METHOD"] == "POST") { $name = $_POST["name"]; $email = $_POST["email"]; echo "Name: $name<br>"; echo "Email: $email"; } ?> |
Incorporation of files
External files can be included in a PHP script. There are four different instructions for this.
1 2 3 4 | require 'pfad/data.php'; include 'pfad/data.php'; require_once 'pfad/data.php'; include_once 'pfad/data.php'; |
This article provided a short overview of PHP basics, covering syntax, variables, control structures, functions, and form handling. By practicing these concepts and exploring more advanced topics, you’ll gain proficiency in PHP development and be well-equipped to build dynamic and interactive web applications. Remember to experiment with code examples, refer to documentation, and engage with the PHP community to deepen your understanding and enhance your skills.
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