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PHP Interview Questions

Top 50 most asked PHP interview questions along with brief answers and examples:

1. What is PHP?

   - PHP stands for Hypertext Preprocessor. It is a server-side scripting language used for web development.

2. Explain the difference between echo Land print.

   - Both are used to output data, but echo can take multiple parameters, while print can only take one.

3. What is the difference between == and === ?

   - == checks equality only, while === checks both value and data type.

4. How do you declare a constant in PHP?

   - Use the define() function, for example: define('MY_CONSTANT', 'value');

5. Explain the use of mysqli and PDO.

   - They are PHP extensions for interacting with databases. mysqli is specific to MySQL, while

PDO supports multiple database systems.

6. What is the use of the implode() function?

   - It joins array elements with a string. Example:

implode(', ', $array);

7. How to prevent SQL injection in PHP?

   - Use prepared statements and parameterized queries.

8. What is the ternary operator and how is it used?

   - It's a shorthand for an if-else statement. Example:

$result = ($condition) ? 'true' : 'false';

9. How can you execute a PHP script from the command line?

   - Use the php command followed by the script name.

10. Explain the concept of sessions in PHP.

- Sessions allow you to store user information on the server, accessible across multiple pages.

11. What is the purpose of the header() function in PHP?

- It sends a raw HTTP header to the browser, often used for redirection.

12. Differentiate between include and require in PHP.

- Both include a file, but require generates a fatal error if the file is not found, while include only produces a warning.

13. What is the purpose of the array_map() function?

- It applies a callback function to each element of an array and returns a new array.

14. How do you handle errors in PHP?

- Use try , catch , and finally blocks for exception handling.

15. Explain the purpose of the $_SESSION variable.

- It is a superglobal variable used to store session variables.

16. What is the use of the foreach loop in PHP?

- It is used to iterate over arrays or objects. Example:


   foreach ($array as $value) {

       // code to execute



17. How can you upload a file using PHP?

- Use the $_FILES array along with the move_uploaded_file() function.

18. What is the purpose of the unset() function?

- It is used to destroy variables or elements within an array.

19. Explain the difference between session_start()

and session_regenerate_id().

- session_start() initializes a new session or resumes an existing one, while session_regenerate_id() regenerates the session ID to help prevent session fixation attacks.

20. How can you validate email addresses in PHP?

- Use the filter_var() function with the FILTER_VALIDATE_EMAIL filter.

21. What is the use of the array_merge() function?

- It merges two or more arrays into a single array.

22. How do you connect to a MySQL database using PHP?

- Use mysqli or PDO along with appropriate connection parameters.

23. Explain the purpose of the header() function in relation to caching.

- It can be used to control caching by sending appropriate HTTP headers.

24. How do you handle file uploads securely in PHP?

- Use move_uploaded_file() , ensure proper file type validation, and use a unique name for uploaded files.

25. What is the use of the count() function in PHP?

- It returns the number of elements in an array or the number of properties in an object.

26. How can you prevent Cross-Site Scripting (XSS) attacks in PHP?

- Use htmlspecialchars() to convert special characters to HTML entities.

27. Explain the difference between GET and POST methods.

- GET appends data to the URL, while POST sends data in the HTTP request body.

28. What is the purpose of the file_get_contents()


- It reads the entire content of a file into a string.

29. How can you set and get cookies in PHP?

- Use setcookie() to set cookies and $_COOKIE

to retrieve them.

30. Explain the purpose of the __construct() method in a PHP class.

- It is called when an object is created, allowing you to perform initialization tasks.

31. What is the use of the array_key_exists()


- It checks if a specific key exists in an array.

32. Explain the difference between == and != and <>.

- != and <> both check for inequality, similar to ==.

33. How can you set a variable to be accessible in multiple scripts?

- Use the session or cookie mechanism to store and retrieve variables across multiple pages.

34. What is the purpose of the spl_autoload_register()


- It registers a function to be called when a class is not found, allowing for custom class loading.

35. How do you use the htmlspecialchars() function to prevent XSS attacks?

- Example:


   $user_input = '<script>alert("XSS");</script>';

   $safe_output = htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');


36. Explain the use of the array_search() function.

- It searches for a value in an array and returns the corresponding key if successful.

37. What is the purpose of the file_exists() function?

- It checks if a file or directory exists.

38. How do you create a function in PHP?

- Example:


   function greet($name) {

       echo "Hello, $name!";



39. How can you retrieve data sent through the URL in PHP?

- Use $_GET superglobal array.

40. What is the ternary shorthand for an if-else statement?

- Example:


   $result = ($condition) ? 'true' : 'false';


41. Explain the purpose of the ob_start() and ob_end_flush() functions..

- ob_start() begins output buffering, and

ob_end_flush() flushes the buffer and ends output buffering.

42. What is the use of the array_flip() function?

- It exchanges the keys and values of an array.

43. How do you prevent session hijacking in PHP?

- Use session_regenerate_id() to regenerate the session ID.

44. What is the purpose of the strtotime() function?

- It parses an English textual datetime into a Unix timestamp.

45. Explain the purpose of the array_reverse()


- It returns an array with elements in reverse order.

46. How can you redirect a user to another page in PHP?

- Use the header() function for redirection. Example:


   header("Location: new_page.php");


47. What is the use of the is_numeric() function?

- It checks if a variable is a number or a numeric string.

48. How do you use the array_diff() function?

- It returns the difference between arrays. Example:


   $difference = array_diff($array1, $array2);


49. What is the purpose of the json_encode()


- It converts a PHP array or object into a JSON string.

50. Explain the use of thevcurlvextension in PHP.

- It is used to make HTTP requests and handle responses.

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