PHP, or Hypertext Preprocessor, is a server-side scripting language that has become the backbone of dynamic web development. It allows developers to create interactive and engaging websites by embedding code directly into HTML. With its versatility and ease of use, PHP powers over 79% of all websites whose server-side language is known, as per recent statistics. For those looking to learn more about PHP's capabilities and features, resources like PHP Manual provide invaluable information.

One of the key advantages of using PHP is its seamless integration with various database systems, particularly MySQL. This enables developers to create data-driven applications with relative ease. PHP supports a wide array of frameworks, such as Laravel and Symfony, which further enhance its functionality and streamline the development process. To grasp the importance of PHP in today’s web landscape and explore its potential, check out articles on reputable sites like W3Schools and TutorialsPoint.

For every PHP developer, mastering the language involves understanding its fundamental functions that boost productivity and coding efficiency. Here are 10 essential PHP functions that every developer should know:

1. strlen() - This function returns the length of a given string, which is crucial when handling user input.
2. array_push() - Adds one or more elements to the end of an array, making data management seamless.
3. implode() - Converts an array into a string by concatenating its elements, useful for displaying data.
4. explode() - Splits a string into an array based on a specified delimiter, an essential feature for parsing data.
5. json_encode() - Converts PHP arrays or objects into a JSON format, facilitating data interchange between server and client.

Additionally, these functions enhance the ability to manipulate strings and arrays, which are core to effective programming in PHP. Other important functions include strpos() for finding the position of a substring within a string, and isset() for checking if a variable is declared and is not null. Mastering these PHP functions not only simplifies coding but also greatly improves performance.

For more insights, check out PHP Manual on strlen() and array_push().

Building a secure and scalable web application with PHP involves several crucial steps. First, it is essential to implement strong security practices to protect your application from vulnerabilities. This includes using prepared statements to prevent SQL injection attacks, validating and sanitizing user inputs, and employing HTTPS for secure data transmission. Additionally, consider using libraries such as FastRoute for efficient routing, which can help enhance performance as your web application grows. Remember, addressing security from the start can save you from significant issues later on.

When it comes to scalability, PHP offers multiple strategies to handle increased traffic effectively. Start by optimizing your database queries and making use of PDO for efficient data handling. Implementing caching mechanisms, such as Redis or Memcached, can significantly reduce server load and improve response times. Furthermore, consider adopting a microservices architecture, as it allows for independent scaling of different components and better resource allocation. For more in-depth guidance, check out this SitePoint article on scalable PHP applications.