PHP
- PHP: A Beginner's Guide for Wiki Contributors
PHP (Hypertext Preprocessor) is a widely-used, open-source scripting language particularly suited for web development and can be embedded into HTML. It's a crucial component of many dynamic websites, powering everything from simple contact forms to complex e-commerce platforms. This article provides a comprehensive introduction to PHP, geared towards individuals contributing to a MediaWiki environment who may want to understand how PHP is used to enhance wiki functionality or develop custom extensions. While this guide doesn't focus on MediaWiki-specific PHP coding (that's covered in Developing MediaWiki extensions), it provides the foundational knowledge necessary to grasp that more advanced topic.
- What is PHP and Why Use It?
PHP isn’t a markup language like HTML, nor is it a compiled language like C++ or Java. It’s an *interpreted* language. This means the PHP code is executed on the server, and the resulting HTML (or other output) is sent to the user’s browser. This contrasts with client-side scripting like JavaScript, which is executed in the user’s browser.
Here’s why PHP is so popular:
- **Open Source:** PHP is free to use and distribute, reducing development costs.
- **Easy to Learn:** Compared to other languages, PHP has a relatively gentle learning curve, especially for those already familiar with HTML.
- **Large Community:** A huge online community provides ample resources, documentation, and support.
- **Database Integration:** PHP seamlessly integrates with popular databases like MySQL, PostgreSQL, and Oracle. This is vital for dynamic websites that require data storage and retrieval. Understanding Database Queries is important in this context.
- **Cross-Platform Compatibility:** PHP runs on various operating systems (Windows, Linux, macOS) and web servers (Apache, Nginx, IIS).
- **Frameworks:** Robust frameworks like Laravel, Symfony, and CodeIgniter streamline development and promote best practices.
- Basic PHP Syntax
Let's look at some fundamental PHP syntax. All PHP code blocks must be enclosed within special tags: `<?php` and `?>`. Anything between these tags is interpreted as PHP code.
```php <?php
echo "Hello, World!";
?> ```
This code snippet will output "Hello, World!" to the browser.
- **Statements:** PHP statements are terminated with a semicolon (;).
- **Variables:** Variables are used to store data. They are prefixed with a dollar sign ($).
```php <?php
$name = "John Doe"; $age = 30; echo "My name is " . $name . " and I am " . $age . " years old.";
?> ```
- **Data Types:** PHP supports various data types, including:
* **String:** Text enclosed in single or double quotes (e.g., "Hello", 'World'). * **Integer:** Whole numbers (e.g., 10, -5, 0). * **Float:** Decimal numbers (e.g., 3.14, -2.5). * **Boolean:** True or false values. * **Array:** A collection of values. * **Object:** Instances of classes. * **NULL:** Represents a variable with no value.
- **Comments:** Comments are used to explain code and are ignored by the interpreter.
* Single-line comments: `// This is a single-line comment` * Multi-line comments: `/* This is a multi-line comment */`
- Control Structures
Control structures allow you to control the flow of execution in your PHP code.
- **`if` Statements:** Execute code based on a condition.
```php <?php
$x = 10; if ($x > 5) { echo "x is greater than 5"; }
?> ```
- **`elseif` Statements:** Provide an alternative condition if the first `if` condition is false.
```php <?php
$x = 5; if ($x > 5) { echo "x is greater than 5"; } elseif ($x < 5) { echo "x is less than 5"; } else { echo "x is equal to 5"; }
?> ```
- **`while` Loops:** Execute a block of code repeatedly as long as a condition is true.
```php <?php
$i = 1; while ($i <= 5) { echo $i . " "; $i++; }
?> ```
- **`for` Loops:** Execute a block of code a specified number of times.
```php <?php
for ($i = 1; $i <= 5; $i++) { echo $i . " "; }
?> ```
- **`foreach` Loops:** Iterate over arrays.
```php <?php
$colors = array("red", "green", "blue"); foreach ($colors as $color) { echo $color . " "; }
?> ```
- Functions
Functions are reusable blocks of code that perform a specific task.
```php <?php
function greet($name) { return "Hello, " . $name . "!"; }
$message = greet("John"); echo $message;
?> ```
- Working with Forms
PHP is commonly used to process data submitted through HTML forms.
- HTML Form:**
```html <form action="process_form.php" method="post">
<label for="name">Name:</label>
<input type="text" id="name" name="name">
<input type="submit" value="Submit">
</form> ```
- PHP (process\_form.php):**
```php <?php
if ($_SERVER["REQUEST_METHOD"] == "POST") { $name = $_POST["name"]; echo "Hello, " . htmlspecialchars($name) . "!"; // Use htmlspecialchars to prevent XSS attacks }
?> ```
- `$_POST`: An associative array containing the data submitted via the POST method.
- `htmlspecialchars()`: Converts special characters to HTML entities, preventing cross-site scripting (XSS) attacks. This is **crucial** for security.
- Databases and PHP
PHP excels at interacting with databases. The most common method is using MySQL with the `mysqli` extension.
```php <?php
$servername = "localhost"; $username = "username"; $password = "password"; $dbname = "myDB";
// Create connection $conn = new mysqli($servername, $username, $password, $dbname);
// Check connection if ($conn->connect_error) { die("Connection failed: " . $conn->connect_error); }
$sql = "SELECT id, firstname, lastname FROM MyGuests"; $result = $conn->query($sql);
if ($result->num_rows > 0) { // output data of each row while($row = $result->fetch_assoc()) { echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "
"; } } else { echo "0 results"; } $conn->close();
?> ```
This code connects to a MySQL database, executes a query, and displays the results. Understanding SQL injection vulnerabilities and how to prevent them is paramount when working with databases.
- PHP and Security
Security is a critical aspect of PHP development. Here are some key points:
- **Input Validation:** Always validate user input to prevent malicious data from being processed.
- **Output Encoding:** Use `htmlspecialchars()` to encode output to prevent XSS attacks.
- **Prepared Statements:** Use prepared statements with parameterized queries to prevent SQL injection attacks.
- **Secure File Uploads:** Implement robust checks to prevent malicious files from being uploaded.
- **Regular Updates:** Keep PHP and any related libraries up to date to patch security vulnerabilities. See Security Best Practices for more details.
- PHP Frameworks
While you can write PHP code from scratch, using a framework can significantly speed up development and improve code quality. Some popular frameworks include:
- **Laravel:** A popular, full-stack framework known for its elegant syntax and extensive features.
- **Symfony:** A robust framework that provides a solid foundation for complex applications.
- **CodeIgniter:** A lightweight framework that’s easy to learn and use.
- **CakePHP:** A rapid development framework that follows the convention-over-configuration principle.
- PHP Versions and Compatibility
PHP is constantly evolving. It’s crucial to be aware of the different versions and their compatibility. As of late 2023, PHP 8.x is the current stable version, offering significant performance improvements and new features. Always check the compatibility of your code with the PHP version running on your server. Consider PHP Compatibility Checks before deploying updates.
- Advanced Concepts (Brief Overview)
- **Object-Oriented Programming (OOP):** PHP supports OOP principles like encapsulation, inheritance, and polymorphism. Understanding OOP is crucial for building maintainable and scalable applications.
- **Namespaces:** Help organize code and avoid naming conflicts.
- **Traits:** Allow code reuse in PHP without the limitations of single inheritance.
- **Error Handling:** Using `try...catch` blocks to handle exceptions gracefully.
- **Sessions and Cookies:** For managing user state and tracking user activity.
- Resources for Further Learning
- **PHP Manual:** [1](https://www.php.net/manual/en/) - The official PHP documentation.
- **W3Schools PHP Tutorial:** [2](https://www.w3schools.com/php/) - A beginner-friendly tutorial.
- **PHP The Right Way:** [3](https://www.phptherightway.com/) - A guide to modern PHP best practices.
- **Stack Overflow:** [4](https://stackoverflow.com/questions/tagged/php) - A question-and-answer website for programmers.
- Understanding Market Trends & Technical Analysis
While PHP powers the backend of many trading platforms, understanding market dynamics is crucial for successful trading. Here are some resources and related concepts:
- **Technical Analysis:** [5](https://www.investopedia.com/terms/t/technicalanalysis.asp)
- **Fundamental Analysis:** [6](https://www.investopedia.com/terms/f/fundamentalanalysis.asp)
- **Moving Averages:** [7](https://www.investopedia.com/terms/m/movingaverage.asp)
- **Relative Strength Index (RSI):** [8](https://www.investopedia.com/terms/r/rsi.asp)
- **MACD (Moving Average Convergence Divergence):** [9](https://www.investopedia.com/terms/m/macd.asp)
- **Fibonacci Retracements:** [10](https://www.investopedia.com/terms/f/fibonacciretracement.asp)
- **Bollinger Bands:** [11](https://www.investopedia.com/terms/b/bollingerbands.asp)
- **Candlestick Patterns:** [12](https://www.investopedia.com/terms/c/candlestick.asp)
- **Trend Lines:** [13](https://www.investopedia.com/terms/t/trendline.asp)
- **Support and Resistance Levels:** [14](https://www.investopedia.com/terms/s/supportandresistance.asp)
- **Elliott Wave Theory:** [15](https://www.investopedia.com/terms/e/elliottwavetheory.asp)
- **Ichimoku Cloud:** [16](https://www.investopedia.com/terms/i/ichimoku-cloud.asp)
- **Market Sentiment Analysis:** [17](https://www.investopedia.com/terms/m/marketsentiment.asp)
- **Volume Analysis:** [18](https://www.investopedia.com/terms/v/volume.asp)
- **Gap Analysis:** [19](https://www.investopedia.com/terms/g/gap.asp)
- **Head and Shoulders Pattern:** [20](https://www.investopedia.com/terms/h/headandshoulders.asp)
- **Double Top/Bottom:** [21](https://www.investopedia.com/terms/d/doubletop.asp)
- **Triangles (Ascending, Descending, Symmetrical):** [22](https://www.investopedia.com/terms/t/triangle.asp)
- **Bearish vs Bullish Trends:** [23](https://www.investopedia.com/terms/b/bullmarket.asp) & [24](https://www.investopedia.com/terms/b/bearmarket.asp)
- **Divergence in Technical Analysis:** [25](https://www.investopedia.com/terms/d/divergence.asp)
- **Correlation in Trading:** [26](https://www.investopedia.com/terms/c/correlationcoefficient.asp)
- **Risk Management Strategies:** [27](https://www.investopedia.com/terms/r/riskmanagement.asp)
- **Position Sizing:** [28](https://www.investopedia.com/terms/p/position-sizing.asp)
- **Stop-Loss Orders:** [29](https://www.investopedia.com/terms/s/stop-lossorder.asp)
PHP Functions PHP Variables PHP Security PHP and Databases PHP Control Structures MediaWiki Development MediaWiki API MediaWiki Extensions Developing MediaWiki extensions Database Queries
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