Top 50 PHP Interview Questions and Answers (2025)

PHP remains one of the most widely used server-side programming languages, powering millions of websites and applications. Whether you’re a beginner or an experienced developer, preparing for a PHP interview is crucial. This guide covers 50 PHP interview questions and answers to help you succeed in 2025.

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Basic PHP Interview Questions

1. What is PHP?

Answer: PHP (Hypertext Preprocessor) is a widely-used open-source scripting language designed for web development. It can be embedded into HTML and executed on the server side.

2. What are the main features of PHP?

Answer:

• Open-source and free
• Cross-platform compatibility
• Embedded in HTML
• Supports multiple databases (MySQL, PostgreSQL, MongoDB, etc.)
• Rich built-in functions
• Supports Object-Oriented Programming (OOP)
• Secure with built-in security features

3. What are PHP variables and how are they declared?

Answer: PHP variables are declared using the $ symbol and do not require explicit data type declaration.

$name = "John";
$age = 25;
echo "Name: $name, Age: $age";

4. What are the different data types in PHP?

Answer:

• String: Holds text (e.g., $name = "John";)
• Integer: Holds whole numbers (e.g., $age = 25;)
• Float: Holds decimal numbers (e.g., $price = 10.5;)
• Boolean: Holds true or false
• Array: Holds multiple values (e.g., $colors = array("red", "blue");)
• Object: Instances of user-defined classes
• NULL: Represents a variable with no value

5. What is the difference between echo and print in PHP?

Answer:

• echo can output multiple values and is slightly faster.
• print returns 1 and can only output one argument.

echo "Hello, World!";
print "Hello, PHP!";

6. What are PHP superglobals?

Answer: Superglobals are built-in global arrays that allow access to various types of data.

• $_GET – Retrieves URL parameters
• $_POST – Retrieves form data
• $_SESSION – Stores user session data
• $_COOKIE – Stores cookie data
• $_SERVER – Retrieves server information
• $_FILES – Handles file uploads

7. What is the difference between == and === in PHP?

Answer:

• == checks for value equality.
• === checks for both value and type equality.

$a = 5;
$b = "5";
var_dump($a == $b);  // true
var_dump($a === $b); // false

8. How does PHP handle sessions?

Answer: Sessions store user data across multiple pages.

session_start();
$_SESSION['username'] = "JohnDoe";
echo $_SESSION['username'];

9. What are PHP cookies?

Answer: Cookies store small pieces of information in the user’s browser.

setcookie("user", "JohnDoe", time() + (86400 * 30), "/");

10. What is the difference between include and require?

Answer:

• include gives a warning if the file is missing but continues execution.
• require makes it mandatory for the file to be present script execution stops with fatal error if the file is missing.

include "header.php";
require "config.php";

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

Answer: Using MySQLi or PDO:

$mysqli = new mysqli("localhost", "username", "password", "database");
if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}

12. What is PDO in PHP?

Answer: PDO (PHP Data Objects) is a database abstraction layer that allows secure interaction with multiple databases.

$pdo = new PDO("mysql:host=localhost;dbname=testdb", "root", "");

13. How do you handle errors in PHP?

Answer: Using try-catch blocks to handle exceptions and errors.

try {
    throw new Exception("An error occurred");
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

14. What is isset() and empty() in PHP?

Answer:

• isset(): Checks if a variable exists and is not null.
• empty(): Checks if a variable contains a falsy value.

$var = "";
var_dump(isset($var)); // true
var_dump(empty($var)); // true

15. How do you redirect a user in PHP?

Answer: Using the header() function:

header("Location: index.php");
exit();

16. How do you send emails in PHP?

Answer: PHP provides the mail() function to send emails, but it’s recommended to use PHPMailer for better reliability and security.

mail("recipient@example.com", "Subject", "Message", "From: sender@example.com");

17. What is a callback function in PHP?

Answer: A callback function is a function that is passed as an argument to another function.

function executeCallback($callback) {
    $callback();
}
executeCallback(function() { echo "Callback executed!"; });

18. How do you perform database transactions in PHP?

Answer: Using PDO transactions ensures data integrity.

$pdo->beginTransaction();
$pdo->exec("INSERT INTO users (name) VALUES ('John')");
$pdo->commit();

19. What are PHP magic methods?

Answer: Magic methods are special methods prefixed with __, such as __construct(), __destruct(), __get(), and __set().

20. What is the difference between self and $this in PHP?

Answer:

• self refers to the class itself and is used with static methods.
• $this refers to the current object instance.

21. How do you encrypt and decrypt data in PHP?

Answer: Use OpenSSL for encryption and decryption.

$encrypted = openssl_encrypt("Hello", "AES-128-CTR", "encryptionkey", 0, "1234567891011121");

22. What is the difference between array_merge() and array_combine()?

Answer:

• array_merge() merges arrays.
• array_combine() combines two arrays, using one as keys and the other as values.

23. What is json_encode() and json_decode() used for?

Answer:

• json_encode() converts an array to JSON.
• json_decode() converts JSON to an array.

$json = json_encode(["name" => "John"]);
$array = json_decode($json, true);

24. What are the different error levels in PHP?

Answer: PHP has multiple error levels, such as E_ERROR, E_WARNING, E_NOTICE.

25. How do you create a custom error handler in PHP?

Answer: Use set_error_handler().

function customErrorHandler($errno, $errstr) {
    echo "Error: [$errno] $errstr";
}
set_error_handler("customErrorHandler");

26. How do you handle file uploads in PHP?

Answer: Use move_uploaded_file().

move_uploaded_file($_FILES['file']['tmp_name'], "uploads/" . $_FILES['file']['name']);

27. What is session_regenerate_id() in PHP?

Answer: It regenerates a new session ID for security purposes.

session_start();
session_regenerate_id(true);

28. What are PHP generators?

Answer: Generators allow iteration without creating large arrays.

function numbers() {
    yield 1;
    yield 2;
}
foreach (numbers() as $num) {
    echo $num;
}

29. How do you define constants in PHP?

Answer: Use define().

define("SITE_NAME", "MyWebsite");
echo SITE_NAME;

30. How do you prevent SQL injection?

Answer: Use prepared statements with PDO.

$stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?");
$stmt->execute([$email]);

31. What is REST API?

Answer: REST stands for REpresentational State Transfer, REST API allows interaction between applications using HTTP methods like GET, POST, PUT, DELETE.

32. How do you generate a random string in PHP?

Answer: Use bin2hex(random_bytes(10)).

33. How do you create a singleton class?

Answer: A singleton ensures a single instance of a class.

class Singleton {
    private static $instance;
    private function __construct() {}
    public static function getInstance() {
        if (!self::$instance) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }
}

34. What is the difference between final and static in PHP?

Answer:

• final prevents method overriding or class from being extended.
• static belongs to the class rather than an instance.

35. What is OAuth authentication?

Answer: OAuth is an authorization framework used for token-based authentication.

36. How does PHP support object cloning?

Answer: Use the clone keyword.

$obj1 = new MyClass();
$obj2 = clone $obj1;

37. What are PHP interfaces?

Answer: Interfaces enable multiple inheritance in PHP OOPs architecture by having method signatures that must be implemented in classes which implements that interface.

38. How do you handle JSON responses in PHP?

Answer:

header("Content-Type: application/json");
echo json_encode(["message" => "Success"]);

39. How do you handle large file uploads?

Answer: Modify php.ini settings:

upload_max_filesize = 100M
post_max_size = 100M

40. How do you handle memory-efficient data processing in PHP?

Answer: Processing large datasets efficiently can be done using generators instead of loading everything into memory at once.

function getData() {
    for ($i = 1; $i <= 1000000; $i++) {
        yield $i;
    }
}

foreach (getData() as $number) {
    echo $number . " ";
}

41. What is the difference between file_get_contents() and fopen() in PHP?

Answer:

• file_get_contents() reads an entire file into a string.
• fopen() opens a file for reading or writing, providing more control.

$content = file_get_contents("example.txt");
$file = fopen("example.txt", "r");

42. How do you check if a string contains a specific word in PHP?

Answer: Use strpos() to check for the presence of a substring.

if (strpos("Hello World", "World") !== false) {
    echo "Found!";
}

43. How do you create and write to a file in PHP?

Answer: Use fopen() with fwrite() to create and write to a file.

$file = fopen("newfile.txt", "w");
fwrite($file, "Hello, PHP!");
fclose($file);

44. How do you measure script execution time in PHP?

Answer: Use microtime(true) at the start and end of the script.

$start = microtime(true);
// Code execution
$end = microtime(true);
echo "Execution time: " . ($end - $start) . " seconds";

45. What are PHP streams and how do they work?

Answer: PHP streams allow reading and writing data using standard protocols such as HTTP, FTP, and file handling.

$handle = fopen("php://input", "r");
$data = stream_get_contents($handle);

46. What is the difference between unlink() and unset() in PHP?

Answer:

• unlink(): Deletes a file from the server.
• unset(): Destroys a variable.

unlink("file.txt");
unset(\$variable);

47. How do you implement JWT authentication in PHP?

JWT (JSON Web Token) is a widely used method for handling user authentication and authorization in a stateless manner, especially in web applications. Here’s how you can implement JWT authentication in PHP:

Steps:

1. Install JWT Library: The easiest way to handle JWT in PHP is by using a library like firebase/php-jwt. You can install it via Composer:composer require firebase/php-jwt
2. Create JWT (Token Generation): When a user logs in or when an API request is made, you generate a JWT to authenticate future requests. The JWT typically contains a header, payload, and a signature.Example code to generate the JWT:use \Firebase\JWT\JWT; $key = "your_secret_key"; // Replace this with your own secret key $issuedAt = time(); $expirationTime = $issuedAt + 3600; // jwt valid for 1 hour from the issued time $payload = array( "iat" => $issuedAt, "exp" => $expirationTime, "userId" => $userId, // Pass user-specific data (e.g., user ID) ); $jwt = JWT::encode($payload, $key); echo json_encode(array("jwt" => $jwt));
3. Verify JWT (Token Validation): On each API request that requires authentication, you need to validate the JWT sent by the user, typically in the Authorization header.Example code to validate the JWT:use \Firebase\JWT\JWT; $key = "your_secret_key"; // Get JWT from Authorization header $headers = getallheaders(); $jwt = null; if (isset($headers['Authorization'])) { $matches = []; preg_match('/Bearer (.+)/', $headers['Authorization'], $matches); if (!empty($matches[1])) { $jwt = $matches[1]; } } if ($jwt) { try { $decoded = JWT::decode($jwt, $key, array('HS256')); // Access the decoded data (e.g., userId) here } catch (Exception $e) { echo json_encode(array("message" => "Access denied. Invalid token.")); } } else { echo json_encode(array("message" => "Token not provided.")); }
4. Using JWT in your application: Once the token is validated, you can use the decoded data (e.g., user ID) to perform authorized actions, such as fetching user-specific resources.

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48. What is the difference between SOAP and REST?

SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) are both web service communication protocols, but they have different characteristics.

SOAP:

• Protocol-based: SOAP is a strict protocol with defined rules for request and response.
• XML-Based: SOAP messages are always sent as XML, which is verbose and can be more complex to handle.
• Stateful: SOAP can support stateful operations, which means it can maintain a session and offer more complex transactional operations.
• Security: SOAP supports WS-Security, a set of standards for secure messaging, making it ideal for applications requiring high security (e.g., banking systems).
• Transport Protocols: SOAP can work over multiple protocols like HTTP, SMTP, and more.
• Complexity: SOAP is more rigid in structure and requires more overhead (WSDL file, schema, etc.).

REST:

• Architecture Style: REST is an architectural style, not a protocol, that uses the existing HTTP methods (GET, POST, PUT, DELETE).
• Data Formats: REST is flexible regarding data formats and can use XML, JSON, or even plain text, with JSON being the most common.
• Stateless: REST is stateless, meaning each request from a client to the server must contain all the necessary information to understand the request.
• Security: REST uses standard security mechanisms like SSL/TLS for secure communication.
• Transport Protocol: REST is designed to work specifically with HTTP.
• Simplicity: REST is lightweight, easy to use, and more scalable than SOAP.

When to use SOAP:

• Complex and highly secure services, such as payment systems or enterprise applications.

When to use REST:

• Lightweight, fast, and stateless communication, often used in web and mobile applications.

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49. How do you handle WebSockets in PHP?

WebSockets allow for bi-directional, real-time communication between the server and client, often used for live chat applications, notifications, or real-time updates.

Steps to handle WebSockets in PHP:

1. Install a WebSocket Server: PHP doesn’t natively support WebSockets, so you need to use a WebSocket server library such as Ratchet or Swoole.Install Ratchet using Composer:composer require cboden/ratchet
2. Create a WebSocket Server (using Ratchet as an example):use Ratchet\MessageComponentInterface; use Ratchet\ConnectionInterface; class WebSocketServer implements MessageComponentInterface { public function onOpen(ConnectionInterface $conn) { echo "New connection: {$conn->resourceId}\n"; } public function onMessage(ConnectionInterface $from, $msg) { echo "Message from {$from->resourceId}: $msg\n"; // Broadcast the message to all connected clients foreach ($from->httpRequest->getServerParams()['ratchet']->getConnections() as $client) { if ($from !== $client) { $client->send($msg); } } } public function onClose(ConnectionInterface $conn) { echo "Connection closed: {$conn->resourceId}\n"; } public function onError(ConnectionInterface $conn, \Exception $e) { echo "Error: {$e->getMessage()}\n"; $conn->close(); } } $server = IoServer::factory(new HttpServer(new WsServer(new WebSocketServer())), 8080); $server->run();
3. Client-Side WebSocket Implementation: You need JavaScript on the client side to connect to the WebSocket server:const socket = new WebSocket('ws://localhost:8080'); socket.onopen = () => { console.log("Connected to WebSocket server."); }; socket.onmessage = (event) => { console.log('Message from server: ', event.data); }; socket.onerror = (error) => { console.error('WebSocket Error: ', error); };
4. Running the WebSocket Server: Run the PHP WebSocket server script, which will listen for incoming connections:php websocket-server.php

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50. How do you optimize PHP performance?

Optimizing PHP performance is critical for improving the speed and scalability of applications. Below are strategies for PHP performance optimization:

1. Use an Opcode Cache: Opcode caching stores precompiled script bytecode in memory, so PHP doesn’t have to parse and compile code on every request. Tools like OPcache (bundled with PHP) can dramatically improve performance.
   • Enable OPcache in the php.ini file:opcache.enable=1 opcache.memory_consumption=128 opcache.interned_strings_buffer=8 opcache.max_accelerated_files=10000
2. Optimize Database Queries:
   • Use indexed columns in database queries to reduce lookup times.
   • Avoid N+1 query problems by using efficient joins or batch queries.
   • Cache database results when possible.
3. Avoid Unnecessary Loops: Ensure you avoid nested loops where possible. Reduce time complexity by using better algorithms or pre-processing data in fewer iterations.
4. Profile and Benchmark: Use profiling tools like Xdebug to identify bottlenecks in your application. Also, consider using Blackfire.io for detailed performance analysis.
5. Optimize Static Content Delivery: Use a Content Delivery Network (CDN) for delivering static assets like images, JavaScript, and CSS to reduce load times. Also, leverage browser caching for static resources.
6. Optimize File I/O: Use proper file handling techniques such as reading from files in chunks and avoiding unnecessary disk I/O. When dealing with large files, use efficient PHP functions for reading/writing.
7. Minimize HTTP Requests: Reduce the number of HTTP requests by combining CSS and JavaScript files. Minify these files to reduce their size.
8. Use Content Compression: Enable GZIP compression in your web server to reduce the size of HTTP responses, improving page load times.

By employing these strategies, PHP applications can be optimized for both speed and scalability.

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These 50 PHP interview questions and answers provide a strong foundation for your next interview in 2025. Let us know in the comments if any other questions you want to be added to this blog or need more detailed answer.