Most Asked PHP Interview Questions

PHP remains one of the most widely used server-side scripting languages for web development. Whether you’re a fresher or an experienced developer, preparing for a PHP interview can be overwhelming. To help you get ready, we’ve curated the most asked PHP interview questions, along with answers, that interviewers expect from candidates. This article will not only serve as a guide for your interview preparation but also give you valuable insights into what the interview process entails.

Table of Contents

1. Introduction to PHP
2. Basic PHP Interview Questions
3. PHP Functions and Arrays
4. Object-Oriented PHP Interview Questions
5. Advanced PHP Interview Questions
6. PHP Database Interaction
7. PHP Security Best Practices
8. PHP in Web Development
9. Conclusion

1. Introduction to PHP

PHP, which stands for Hypertext Preprocessor, is an open-source scripting language primarily used for web development. It can be embedded into HTML and works on the server side, making it a powerful tool for dynamic web applications. Since its inception in 1994, PHP has powered millions of websites, including big names like Facebook, WordPress, and Wikipedia.

When preparing for PHP interviews, focusing on key topics like syntax, OOP concepts, database interaction, and security is crucial. We’ve organized a selection of the most common PHP interview questions to assist you in succeeding in your interview.

2. Basic PHP Interview Questions

Here are the fundamental questions that every PHP developer should know:

1. What is PHP?
   PHP is a server-side scripting language used for building dynamic websites and applications.
2. How do you declare variables in PHP?
   Variables in PHP start with a $ symbol, like $variableName.
3. What are the common data types in PHP?
   PHP allows for various data types, including integers, floats, strings, arrays, objects, and booleans.
4. What’s the difference between echo and print?
   Both output data to the screen, but echo can take multiple arguments, while print always returns 1 and accepts only one argument.
5. Explain the differences between the GET and POST methods.
   GET appends form data in the URL, making it visible and insecure, while POST sends data invisibly through the HTTP request body.

3. PHP Functions and Arrays

6. How do you define a function in PHP?
   To define a function, use the function keyword, followed by the name of the function.
7. Describe how indexed arrays differ from associative arrays.
   Indexed arrays use numeric keys (e.g., $array[0]), whereas associative arrays use named keys (e.g., $array['key']).
8. How do you use the array_merge() function?
   This function combines the elements from one or more arrays into a single array.
9. How does isset() differ from empty()?
   The isset() function determines whether a variable has been initialized and isn’t null, whereas empty() checks if the variable has no value or is considered empty.
10. What are superglobals in PHP?
    Superglobals are built-in variables such as $_POST, $_GET, $_SESSION, etc., which are accessible throughout the script.

4. Object-Oriented PHP Interview Questions

11. What is Object-Oriented Programming (OOP)?
    Object-Oriented Programming (OOP) is a coding approach that involves creating objects, which are specific instances of classes. These objects bundle both data and the functions that act on that data.
12. How do you define a class in PHP?
    A class is created by using the ‘class’ keyword, followed by its name and a block of code.
13. Explain inheritance in PHP.
    Inheritance allows a class to inherit properties and methods from another class using the extends keyword.
14. What is polymorphism in PHP?
    Polymorphism enables methods to perform different actions depending on the object invoking them.
15. What are interfaces in PHP?
    Interfaces define a set of methods that any implementing class must define. Interfaces are defined by utilizing the interface keyword.

5. Advanced PHP Interview Questions

16. What role does the namespace serve in PHP?
    Namespaces help avoid name collisions by encapsulating classes, functions, and constants under a unique name.
17. What is a trait in PHP?
    Traits allow you to reuse methods across multiple classes without using inheritance.
18. Explain the difference between require and include.
    require stops the script execution on failure, while include only gives a warning and continues the execution.
19. What strategies can you implement to enhance the performance of a PHP application?
    Common optimizations include using caching (e.g., OPcache), reducing database queries, and employing lazy loading.
20. How do you handle exceptions in PHP?
    PHP uses try, catch, and throw blocks for exception handling.

Also Read: Best HTML Interview Questions for Freshers

6. PHP Database Interaction

21. What is the process for establishing a connection to a MySQL database with PHP?
    You can use mysqli_connect() or PDO for connecting to a MySQL database.
22. What are prepared statements in PHP?
    Prepared statements allow you to execute the same SQL query repeatedly with different values, enhancing security and performance.
23. What is PDO in PHP?
    PHP Data Objects (PDO) is a database access layer providing a uniform method to interact with databases.
24. What are the methods to retrieve data from a MySQL database using PHP?
    You can retrieve data by using either mysqli_fetch_array() or PDO::fetch().
25. Explain the difference between mysqli and PDO.
    mysqli is for MySQL databases only, while PDO supports multiple database systems.

7. PHP Security Best Practices

26. How do you prevent SQL injection in PHP?
    You can avoid SQL injection by employing prepared statements and using parameterized queries.
27. How can you sanitize user input in PHP?
    Use functions like htmlspecialchars() to prevent XSS attacks and filter_var() for validating input.
28. What is cross-site scripting (XSS), and how do you prevent it in PHP?
    XSS refers to a security flaw that allows attackers to insert harmful scripts into web applications. You can prevent XSS by escaping output using htmlentities().
29. How do you manage secure file uploads in PHP?
    Validate file extensions and MIME types, restrict upload sizes, and store files outside the web root.
30. What is Cross-Site Request Forgery (CSRF), and what strategies can you use to prevent it in PHP?
    Cross-Site Request Forgery (CSRF) can be mitigated by using anti-CSRF tokens in forms.

8. PHP in Web Development

31. How do you create a session in PHP?
    Use session_start() to begin a session.
32. How do sessions and cookies differ in PHP?
    Sessions are kept on the server, whereas cookies are saved in the user’s web browser.
33. How can you redirect a user in PHP?
    Utilize the header() function to navigate a user to a different page.
34. How do you send an email using PHP?
    You can send emails using the built-in mail() function or opt for a library such as PHPMailer.
35. What are the steps to build a basic REST API with PHP?
    Use $_GET and $_POST methods to handle REST API requests and return responses in JSON format using json_encode().

Conclusion

These most asked PHP interview questions cover a wide range of topics from basic PHP concepts to advanced techniques, as well as OOP and security practices. No matter if you’re just starting out or have some experience with PHP, grasping these questions will boost your confidence as you get ready for your upcoming interview.

Remember, practice is key! Becoming well-acquainted with these questions and ideas will help you feel more at ease during the real interview.