PHP interview questions

Beginner-Level PHP Interview Questions

1. What is PHP? 

PHP stands for Hypertext Preprocessor. It's an open-source, server-side scripting language designed primarily for web development. PHP scripts are executed on the server, generating HTML that is then sent to the client.

2. What did the acronym PHP originally stand for? 

PHP originally stood for Personal Home Page. This name was used when PHP was first created by Rasmus Lerdorf in 1994.

3. What was the old name of PHP? 

The old name of PHP was PHP/FI, which stood for Personal Home Page/Forms Interpreter. This was the name of the second iteration of PHP, released in 1995.

4. What are 'Traits'? 

Traits are a mechanism for code reuse in single inheritance languages like PHP. They allow developers to reuse sets of methods freely in several independent classes living in different class hierarchies.

5. What are the uses of PHP? 

PHP has several uses, including:

• Server-side scripting for web development
• Command-line scripting
• Writing desktop applications (using PHP-GTK)
• Database operations
• Session handling
• Dynamic content generation

6. What are the characteristics of PHP variables? 

PHP variables have the following characteristics:

• They start with a dollar sign ($)
• They are case-sensitive
• They don't need to be declared before use
• They can hold different types of data
• Their type is determined by the context in which they're used

7. What is the difference between static and dynamic websites? 

Static websites display fixed content for every user, while dynamic websites can display different content and provide user interaction, usually by making use of server-side scripting languages like PHP.

8. What are some of the applications of PHP? 

PHP is used in various applications, including:

• Content Management Systems (e.g., WordPress, Drupal)
• E-commerce platforms (e.g., Magento, PrestaShop)
• Customer Relationship Management (CRM) systems
• Forum software
• Email servers
• Data analysis and visualization tools

9. How to display text with a PHP script? 

To display text with a PHP script, you can use either the echo or print statement. For example:

10. What is the PHP scripting engine called? 

The PHP scripting engine is called Zend Engine. It's the core of PHP and is responsible for interpreting PHP code, managing memory allocation, and providing other essential services.

<?php
echo "Hello, World!";
// or
print "Hello, World!";
?>

11. Describe the steps to create a database using PHP and MySQL?

To create a database using MySQL and PHP, we have to follow the following steps-
Connect MySQL to your PHP script.
After a successful connection, run a SQL query to create a database after storing it in a string variable.

12. What is the $_GET method in PHP?

The $_GET method is a superglobal variable in PHP. These are variables that are always available in PHP in all the scopes. After submitting an HTML form with method = "get," it is used to collect the form data.

13. What is the $_POST  method in PHP?

Like the $_GET  method, it is also a super globe variable and always available in all the scopes. It is also used to submit HTML form data, and if we submit by this method, the data is collected by the $_POST method. Unlike the $_GET  method, the $_POST method has no restriction on the amount of data that can be sent. HTTP header is used to send data in the Post method. ASCII and binary data in both forms can be transferred through this method.

14. What is the function of $_FILES['userfile']['name'] , $_FILES['userfile']['tmp_name'] and $_FILES['userfile']['error'] commands?

• $_FILES['userfile']['name'] - It is used to represent a file's original name on the client's system.
• $_FILES['userfile']['tmp_name']- It is used to represent a file's temporary name while it is stored on the server.
• $_FILES['userfile']['error'] - It is used to contain the error code while uploading a file.

15. What is fopen() in PHP?

fopen() is used to either open or create a file in PHP. If the file already exists, it will be opened, but it will be created first then opened if it does not exist. The file is created in the same directory that contains the PHP scripts.
Syntax-

$newfile = fopen("newfile.txt", “w”)

16. What is $_SERVER  function in php?

It is a superglobal variable and holds the details about the headers, paths, and script locations. we can pass different elements to it to carry out various functions. for example- $_SERVER['PHP_SELF']  will return the currently executing script's filename, and $_SERVER['SERVER_ADDR'] is used to return the host server's  IP address.

17. Describe the use of the session_start() and session_destroy() function?

The session_start() function helps us start a new session. It can also resume the current session which has been stopped and return it if resumed.
The session_destroy() is used to clear any active session.

18. Differentiate between require() and require_once()?

The major difference between require() and require_once() is that require() is used to add a file in PHP, and if it can't find the file, it will produce an error message and stop execution. Whereas, in the case of require_once(), the file is only included if it's not included before. Though it also shows an error message and stops execution if it can't locate the file.

19. What is the __construct() function in PHP?

__construct() function is used to initialize the properties of an object while creating it. If declared, this function is automatically called when an object is created.

20. What is a "__destruct" in PHP?

The "__destruct" function is called at the end of the script to destruct the object. If we create a "__destruct" function, it is called automatically at the end of the script, or there aren't any references to the object anymore.

Intermediate-Level PHP Interview Questions 

21. What is the $_ENV  function in php?

It is a superglobal associative array. It is used to store available environment variables for the current script. A similar function $_HTTP_ENV_VARS  is also used for the same purpose, but it is not a superglobal and has a limited scope. Since the shell of the PHP parser provides these environment variables, thus the environment variables in the function can vary depending on the platform. 

22. What is overriding and overloading in PHP?

Overriding happens when a derived class overrides a method defined in the parent class. Whereas overloading means defining the same functions with different parameters, we use the magic method_call for overriding in PHP.

23. Describe type hinting in PHP?

It helps us specify the type of data we expect to pass as an argument while declaring the function. When the code is executed, whether the arguments have the same data type as specified or not. In the case of different data types, it shows an error message and halts the execution.

24. Describe the callback functions in PHP?

The callback is a function in PHP that can be passed as an argument to another function. It can also be an existing function. To use it as a callback function, we need to pass its name as an argument to another function using string.

25. What is an anonymous function in PHP?

Anonymous functions are also known as closures; these are used to create functions with no specified name. These are implemented using closure classes. They end with a semicolon because they are expressions.

$func = function ($ar1, $ar2) { return $val ; } ;

26. What is the foreach loop in PHP?

It is a looping method in PHP that is used while iterating through an array. It works by assigning a value to the element and incrementing the pointer in each pass. This process gets repeated until we iterate the whole array.

foreach ($arr as $iterator)
{
	//code goes here.
}

27. How do PHP and HTML interact?

PHP is a server-side scripting language, whereas HTML is a client-side language, PHP can generate HTML. Similarly, HTML can also pass information to PHP. PHP gets executed on the server-side, and then it can pass its results to the HTML in the form of strings, objects, arrays, etc.

28. Is it possible for javascript to interact with PHP?

Like generating HTML, PHP can also generate javascript variables, which can be further executed in the browser. And with this, PHP can get variables using URLs.

29. How can we connect to a URL in PHP?

In most cases, the installation of PHP automatically installs a library called cURL, which stands for client URL. It helps us connect to a URL and retrieve the content and data associated with that page, such as HTML, HTTP header, etc.

30. What are global variables in PHP?

Super global variables are predefined variables available across the program, i.e., in all the scopes. they can be used across the program without any special conditions or requirements. The global variables in PHP are as follows-
$_SERVER, $_REQUEST, $_POST, $_GET, $_FILES, $_ENV, $_COOKIE, $_SESSION

31. What is a parser in PHP?

The software used to convert source code into simpler code that the computer can understand is known as the parser. token _get_all function can be used in PHP to parse PHP code.

32. What are traits in PHP?

These mechanisms help us create reusable code in PHP, as PHP doesn't support multiple inheritances. It helps us to bypass the limitations occurring because of single inheritance.

33. What are cookies in PHP?

It is a small record containing the user's information and can be installed on the user's computer by the server. In simple words, it is a bundle of information unique to every URL that is saved on the user's system, and whenever the user tries to access that site, this data is also passed to the site. These mainly help the sites to facilitate users by remembering their preferences each time they visit the site.

34. How are passwords hashed in PHP?

We use the crypt() function for hashing passwords, and the main reason is that it provides large numbers of fast and efficient hashing algorithms like sha1, sha256, and md5.

35. What is asp.net?

ASP.NET is a free, open-source web application framework that can be used on almost any platform. It also can compile and execute code. It allows you to build your web apps using a language called razor, a combination of HTML and C#.

36. What is Memcache in PHP?

It is a storage space for memory. It can be run on single or multiple servers. Several projects might share a single instance of Memcache. Also, we can configure the clients to handle different sets of instances, thus allowing two instances of Memcache to run simultaneously. It will work fine until there is a partition of data among both processes.

Must Read PHP Projects With Source Code and Power Electronics Interview Questions

37. What is Memcached in PHP?

It is a caching daemon(Memcached daemon) specially designed to decrease database load for dynamic web applications. It helps us speed up the database-driven sites by caching the data and other objects in server memory. This decreases the number of times the data source needs to be read.

38. How can we terminate the execution of a script in PHP?

We use the exit() function to terminate the execution of scripts in PHP. This built-in function prints an output message then terminates the execution. The output message can be passed to the exit() function as a parameter. The function first displays the message then terminates the execution.

39. What are interfaces in PHP?

Interfaces in PHP are used to specify the methods a class should implement. Interface keyword is used to declare interfaces, and to implement it, the class must use the implements keyword. Whenever a class implements an interface, it has to implement all the methods in the interface.

40. What are abstract classes and methods in PHP?

Abstract classes have at least one abstract method, which means that the method is declared in the class but has no definition to it. Thus whenever a child class inherits this class, it needs to define these methods. Abstract classes or methods are defined using abstract keywords.

Advanced-Level PHP Interview Questions

41. What are Closures in PHP and how are they used?

Closures in PHP are anonymous functions that can access variables from the outside scope. They are useful for creating callback functions and can be passed as arguments to other functions. Example:

$message = "Hello"; 
$greet = function($name) use ($message) {     
				return "$message, $name!"; 
				}; 
echo $greet("John"); 

42. Explain the difference between __construct() and __destruct() methods in PHP classes.

__construct() is a magic method called automatically when an object is created. It's used to initialize object properties. On the other hand, __destruct() is called when an object is destroyed or the script ends. It's used for cleanup tasks like closing database connections.

43. What is Dependency Injection and why is it important in PHP?

Dependency Injection is a design pattern where objects are passed into a class instead of being created inside it. It's important because:

• It reduces coupling between classes
• It makes testing easier by allowing mock objects to be injected
• It improves code reusability and maintainability

44. How does PHP handle asynchronous programming?

PHP traditionally uses synchronous programming, but asynchronous programming can be achieved using:

• Extensions like ReactPHP or Swoole
• Generators and Coroutines
• Parallel processing with pcntl_fork()
• Job queues and message brokers

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

Generators are functions that can be paused and resumed, yielding multiple values over time. They're memory-efficient for working with large datasets. Example:

function countTo($n) {     
	for ($i = 1; $i <= $n; $i++) {         
			yield $i;     
			} 
} 
foreach (countTo(5) as $number) 
{     
	echo $number . " "; 
}

46. Explain the concept of late static binding in PHP.

Late static binding refers to the runtime resolution of static method calls in inherited classes. It's implemented using the static keyword instead of self. This allows methods to be called on the class they're called from, not the class they're defined in.

47. What are PHPDoc comments and why are they useful?

PHPDoc comments are structured documentation blocks in PHP code. They're useful for:

• Generating API documentation
• Providing type hints for IDEs
• Improving code readability
• Facilitating better collaboration among developers

48. How does PHP's garbage collection work?

PHP uses reference counting for basic garbage collection. When an object's reference count drops to zero, it's deleted. For cyclic references, PHP uses a cycle-collecting algorithm to detect and clean up unreachable object cycles.

49. What are PHP traits and how do they differ from interfaces and abstract classes?

Traits are a mechanism for code reuse in single inheritance languages like PHP. Unlike interfaces, traits can contain method implementations. Unlike abstract classes, multiple traits can be used in a single class.

50. Explain the difference between include, require, include_once, and require_once in PHP.

• include: Includes and evaluates a file, produces a warning on failure
• require: Similar to include, but produces a fatal error on failure
• include_once: Includes the file only if it hasn't been included before
• require_once: Similar to include_once, but produces a fatal error if the file can't be included

51. What are PHP namespaces and how do they help in organizing code?

Namespaces are a way of encapsulating items to avoid name conflicts. They help in organizing code by:

• Avoiding naming collisions between your code and third-party libraries
• Improving code readability and maintainability
• Allowing for shorter, more concise class names within the namespace

52. How does PHP handle session management?

PHP handles sessions using a unique session ID for each user. This ID is usually stored in a cookie on the client-side. Server-side, session data is stored in files or a database. Functions like session_start(), $_SESSION, and session_destroy() are used to manage sessions.

53. What is the difference between mysqli and PDO for database operations in PHP?

• mysqli is specific to MySQL databases, while PDO can work with multiple database types.
• PDO uses named parameters for prepared statements, making it more readable.
• PDO provides a more consistent API across different databases.
• mysqli can be slightly faster for MySQL-specific operations.

54. Explain the concept of method chaining in PHP and provide an example.

Method chaining allows multiple methods to be called in a single statement. It's achieved by returning $this from methods. Example:

class Calculator {
   private $result = 0;
   public function add($num) {
       $this->result += $num;
       return $this;
   }
   public function subtract($num) {
       $this->result -= $num;
       return $this;
   }
   public function getResult() {
       return $this->result;
   }
}
$calc = new Calculator();
echo $calc->add(5)->subtract(3)->add(2)->getResult();

55. What are PHP magic methods and name at least five of them.

Magic methods are special methods that override PHP's default behavior when certain actions are performed on an object. Five examples are:

• __construct()
• __destruct()
• __get()
• __set()
• __call()

56. How does PHP handle type hinting and what are its benefits?

Type hinting in PHP allows specifying the expected data type of function arguments and return values. Benefits include:

• Improved code readability
• Better error detection at runtime
• Enhanced IDE autocomplete and code analysis

For example:

function addNumbers(int $a, int $b): int {     
return $a + $b; 
}

57. What is Composer in PHP and why is it useful?

Composer is a dependency management tool for PHP. It's useful because:

• It automates the process of adding, updating, and removing project dependencies
• It generates an autoloader for efficient class loading
• It allows for easy sharing and reuse of code across projects

58. Explain the concept of reflection in PHP and provide an example use case.

Reflection in PHP allows code to inspect and modify its own structure and behavior at runtime. It's useful for:

• Creating flexible APIs
• Unit testing
• Implementing dependency injection containers

For example, a framework using reflection to automatically map HTTP requests to controller methods based on naming conventions.

59. What are PHP generators and how do they differ from arrays?

Generators allow you to write code that uses foreach to iterate over a set of data without needing to build an array in memory. They differ from arrays in that:

• They generate values on-the-fly, saving memory
• They can represent infinite sequences
• They can only be iterated over once

60. How does PHP handle error handling and exception handling?

PHP uses a combination of error handling and exception handling:

• Error handling uses functions like error_reporting() and set_error_handler() to control how errors are reported and handled.
• Exception handling uses try-catch blocks to handle runtime errors. PHP 7 introduced Error exceptions, allowing most fatal errors to be caught like regular exceptions.

Click on the following link to read further: Javascript Interview Questions and Answers

Conclusion

In this blog, we have discussed the top 50+ PHP interview questions and Answers (2024). Mastering these PHP interview questions will significantly boost your confidence and preparedness for your next PHP developer interview. From fundamental concepts to advanced topics, this blog covers a wide range of PHP knowledge essential for both junior and senior developer positions in 2024.

Related Links:

• C# Interview Questions
• LINQ Interview Questions
• Maven Interview Questions
• SSRS Interview Questions
• Html interview questions
• SQL Query Interview Questions
• Excel Interview Questions
• Operating System Interview Questions
• MySQL Interview Questions
• MongoDB Interview Questions
• MVC Interview Questions
• Servicenow Interview Questions