Top 40 PHP Developer Interview Questions for Beginners, Intermediates, and Experienced Candidates

Approximately 79% of websites using server-side programming rely on PHP. This makes it one of the most popular programming languages, increasing the demand for skilled PHP developers. PHP developers often work on widely known platforms such as WordPress, Lavarel, Facebook, Joomla, and Drupal. Their responsibilities often involve creating dynamic web applications, maintaining existing codebases, and ensuring high engagement of applications. Since the job role is dynamic and complex, candidates are often expected to demonstrate a well-rounded understanding of PHP and its common applications. In this blog, we have listed the 40 common PHP interview questions asked by interviewers.

PHP Developer Interview Questions and Answers

Here is a comprehensive list of PHP interview questions that span from basic concepts to advanced technical questions. Whether you are a fresher, intermediate, or experienced candidate, these questions will help you demonstrate the profound understanding required for a PHP Development job.

i. Basic PHP Developer Interview Questions for Beginners

Preparing for your first interview can be overwhelming at times. These PHP interview questions for freshers are meant to help you highlight your strong understanding of the programming language.

Q1. What does PHP stand for?

Answer: PHP stands for Hypertext Preprocessor. It is an open-source server-side scripting language that is commonly used for web development. This means PHP can process a website before it gets processed in CSS, HTML, or Javascript. Additionally, PHP supports several databases such as Sybase, Solid, PostgreSQL, MySQL, and generic ODBC. 

Q2. What is a session in PHP?

Answer: A session is a way to store single user information to be used across several pages of a website. It is different than a cookie since the information is not stored on the user’s computer. Rather a file is created by the session where registered session variables and their values are stored. This information is further available to all pages on the site.

Q3. What are the common functions of PHP?

Answer: Some of the common functions of a PHP are as follows:

• PHP provides restricted access to the required content of the website.
• It allows users to access individual cookies and set them as per requirement.
• PHP helps in database manipulation operations such as deletion, addition, and modification.
• The system module allows users to perform a variety of system functions, such as open, read, write, etc.

Q4. How is a for loop different from for-each loop?

Answer: For loop is different from for-each loop in the following ways:

For loop	For-each loop
For loop openly executes the iteration.	The for-each loop iterates over the array for simpler syntax.
You can manipulate the index with the for loop.	The for-each loop will directly give you the value.
For loop is difficult to read when dealing with arrays.	You can easily read the for-each loop while dealing with arrays.

Q5. What type of language does PHP use?

Answer: PHP is an open-source scripting language. Therefore, it is neither interpreted nor compiled. PHP has more similarities with Perl and CGI than C or Java. PHP is not compiled as an executable, but rather the script gets executed as it’s read, much like JavaScript.

Tip: You can learn more about the best programming languages to frame a better answer to PHP developer interview questions. 

Q6. How is a variable different from constants in PHP?

Answer: Some of the key differences between variables and constants are as follows:

Variables	Constants
The value of a variable can be changed during execution.	The value of a constant can’t be changed during an execution.
Variables must start with a $ sign.	Constants are not required to start with a $ sign.
Variables can be defined with a simple assignment.	Constants can only be defined with a define() function.
The default scope of the variable is a current access scope.	Constants do not need scoping rules.

Q7. Name the most recent PHP version that was launched.

Answer: The most recent version of PHP was launched in April 2020. It is version 7.2.30, 7.3.17, and 7.4.5 respectively. These versions address the overall security of PHP and improve stability and performance by fixing bugs in the system. Additionally, each version introduced new language features to enhance the user’s experience.

Q8. What is a PEAR in PHP?

Answer: PEAR is short for PHP Extension and Application Repository. It is an online repository of free, open-source PHP software packages, and hosts all of the reusable PHP components. Besides containing PHP libraries, it also provides a simple interface to automatically install packages. PEAR also provides various packages and functions, from database and networking to file system access and remote process control. Additionally, it also includes robust tools to help developers quickly and easily create web-based applications and services.

Q9. Define a LAMP stack.

Answer: LAMP is a common environment for PHP. It refers to a Linux operating environment running an Apache server with MySQL and PHP installed (LAMP). It is a popular framework used for web development, specifically for building websites and applications. It is particularly used for projects that require rapid development and easy deployment.

Q10. What is the difference between $message and $$message?

Answer: The main difference between the $message and the $$message is as follows:

$ message	$$ message
$ message is a regular variable.	$$ message is a reference variable.
$ message has a fixed name and stores a fixed value.	$$ message stores data about the variable.
The value in $ message remains fixed.	The value in $$ message changes as the value of the variable changes.

Q11. What are the popular frameworks in PHP?

Answer: Some of the popular PHP frameworks are:

• CakePHP: It quickly generates code for database interactions and emphasizes convention over configuration and rapid application development.
• CodeIgniter: CodeIgniter is a lightweight framework that is easy to learn and use. It can be setup quickly with minimal configuration.
• Zend Framework: Zend Framework focuses on enterprise-level applications. It also provides support for building APIs.
• Yii 2: Yii 2 is a high-performance framework that is ideal for developing web applications.
• Symfony: It is a highly flexible and powerful framework that follows the MVC architecture.

Q12. How can PHP scripts be executed?

Answer: PHP files can be executed in multiple ways depending on the environment. Some of the most common ways to execute it are:

• Command Line Interface: You can execute your script in the Command Line Interface, by opening it on the terminal and navigating it to the directory containing your script. Now, execute the script using php script.php command.
• Web Server Environment: When PHP is installed on a web server like Apache or Nginx, you can run PHP scripts by placing them in the server’s document root and accessing the file using a URL.

Q13. What is the function of a break and continue statement? 

Answer: In PHP, the break statement helps in terminating the loop or switching a statement. When break is executed, the control exits the loop immediately. On the other hand, when the continue statement is executed, it skips the current iteration of the loop and brings the next iteration. This means no code following the continue statement within the loop will be executed for the iteration.

Q14. Is PHP a case-sensitive language?

Answer: PHP is a partial case-sensitive language. This means the variable names are case-sensitive but the function names are not. Additionally, user-defined functions are not case-sensitive but the remaining language is.

Q15. Who founded PHP and when?

Answer: PHP was founded by Rasmus Lerdorf in 1994. This is a vital piece of information since PHP is an old language and has gone through several changes, but it still retains antiquated hallmarks, such as being able to execute in a runtime environment despite warnings and having limited object-oriented functionality.

ii. PHP Interview Questions for Intermediate Candidates

Intermediate candidates are usually required to demonstrate an understanding of advanced topics as well as the significant evolution of the programming language over the years. Check out these PHP interview questions to help you gain an advanced understanding of PHP.

Q16. What are the different types of variables present in PHP?

Answer: PHP utilizes 8 fundamental data types for variable construction. These include:

• Objects: Objects are instances of classes containing both data and functions.
• Resources: Resources are special variables referencing external PHP resources.
• Doubles: Also known as floating-point numbers.
• NULL: NULL represents a variable with no assigned value.
• Arrays: Arrays are ordered collections of related data elements.
• Booleans: Booleans are logical values representing true or false states.
• Strings: Sequences of characters.
• Integers: Integers are whole numbers without decimal points.

Q17. Name the most popular sites built on PHP.

Answer: WordPress stands out as the most renowned PHP-based platform. Its PHP/MySQL foundation powers a significant portion of websites globally. Other notable PHP-driven systems include content management frameworks like Joomla, Magento, and Drupal. These platforms facilitate website creation for users with varying levels of technical expertise.

Tip: Research and be aware of a few websites built using PHP to answer these types of PHP developer interview questions.

Q18. List the main characteristics of a PHP variable.

Answer: The key aspects of PHP variables include the following:

• No requirement for declaration before value assignment
• Value assignment using the ‘=’ operator
• Prefixing with a ‘$’ symbol
• Values determined by the most recent assignment
• Lack of intrinsic typing or explicit declaration

Q19. What is PHP used for?

Answer: PHP primarily serves as a server-side scripting language for web development. Its capabilities include database interaction, data analysis, and dynamic generation of HTML, JavaScript, and CSS. When combined with JavaScript, PHP can power sophisticated web applications, including progressive web apps.

Q20. Name the programming languages that are similar to PHP.

Answer: Perl and C share similarities with PHP in terms of syntax and structure. However, while PHP has maintained its popularity, Perl and C have seen a decline in web development usage. PHP continues to be a widely adopted language in modern web development practices.

Q21. What are traits of PHP?

Answer: Traits are a method used to resume code in single inheritance languages such as PHP. They assist developers in creating reusable sets of actions that may be included in various classes, hence reducing code duplication.

Q22. Define a PHP function.

Answer: A PHP function is a reusable code block that performs a specific task. It allows developers to organize and modularize their code, improving maintainability and reducing repetition. Functions can accept parameters and return values, enhancing their versatility in various programming scenarios.

Q23. What is the main difference between “echo” and “print” in PHP?

Answer: The key distinctions between echo and print in PHP are depicted in the table below:

Echo	Print
Can output multiple strings.	Outputs a single string and always returns 1.
Faster due to lack of return value.	Slightly slower than echo.
Requires parentheses for multiple parameters.	Doesn’t require parentheses for arguments.

Q24. Differentiate between static and dynamic websites.

Answer: Static websites consist of fixed content stored in files and served directly to users. They require manual editing for updates. In contrast, dynamic websites offer rich, adaptable content that can change based on various factors such as user input or database queries, providing a more interactive and personalized user experience.

Q25. How is PHP5 better than PHP4?

Answer: PHP5 introduced several improvements over PHP4, especially in terms of how developers could structure their code. One major change was the enhanced support for object-oriented programming (OOP). PHP5 allowed for more control with features like private and protected properties, as well as abstract and final classes. It also standardized how constructors and destructors were defined. This has helped in making the code easier to manage and understand. Another useful addition to PHP5 was static methods, which made it possible to call functions without creating an instance of a class.

Q26. Name some of the extensions PHP uses.

Answer: The common PHP file extensions include .PHP, .PHTML, and .PHP5, with .PHP being the most prevalent. However, PHP’s flexible configuration allows for the use of any file extension. Some websites even utilize .HTML extensions for PHP files, relying on server settings to process these files through PHP.

Q27. What are some of the disadvantages of PHP?

Answer: The potential drawbacks of PHP include:

• Limited suitability for large-scale, content-heavy web applications.
• Security concerns due to its open-source nature.
• Restrictions on modifying core behaviors of web applications.
• Performance issues when extensively using PHP frameworks and tools.
• Inadequate error handling and debugging capabilities compared to other languages.

Q28. How can lines be terminated in PHP?

Answer: In PHP, lines are terminated using a semicolon (;). This punctuation mark is crucial for proper code execution and helps prevent syntax errors.

Q29. What is Path Traversal?

Answer: Path traversal is a security vulnerability where attackers manipulate file paths to access sensitive information outside a web application’s intended directory. It often involves using “../” sequences to navigate directory structures, potentially exposing critical system files or confidential data.

Q30. How can you create a comment in PHP?

Answer: PHP supports two comment styles:

1. Single-line comments: Preceded by //
2. Multi-line comments: Enclosed within /* */

Proper commenting enhances code readability and maintenance by explaining functionality and purpose to other developers or future maintainers.

iii. Best PHP Interview Questions for Experienced Candidates

For experienced candidates, these PHP technical interview questions focus on technical expertise and past experiences. Here’s a list of commonly asked PHP interview questions for senior-level job roles.

Q31. What are the rules for naming a PHP variable?

Answer: The rules for naming a variable in PHP are as follows:

• Begin with a $ sign: Each variable must begin with a $ sign to ensure they are valid and contribute to a maintainable code.
• Add underscores or letters: Add letters or underscores after the $ sign. These letters can be both uppercase and lowercase, however, it cannot start with a number.
• Case sensitive: Variables in PHP are highly case sensitive, which means $var and $Var have different values.
• No special characters: Variables must not contain any special characters such as @, %, *, or ^.
• Avoid reserved words: Words such as if, function or class might be incorrectly read by the language’s syntax. Therefore, avoid using reserved words at all costs.

Q32. How can you create a WHILE() loop in PHP?

Answer: You can create a WHILE () loop in the following way:

$int = 1;
	while($int <= 10) {
		print("$int<br>");
		$int = $int+1;
	}

However, it’s important to note that WHILE () loops are barely used in PHP, since they can keep going until they meet certain criteria.

Q33. What do you mean by ‘escaping to PHP’?

Answer: The transition from HTML to PHP code within a document is known as ‘escaping to PHP’. This is done when you want to use PHP logic within an HTML structure. ‘Escaping to PHP’ is done to reduce ambiguity and create webpages that can adapt based on user input, different variables, and server-side logic to increase the interactivity of the web application.

Q34. How can you determine the ‘truth’ in PHP?

Answer: In order to determine the ‘truth’ of any value in PHP, we would have to assess it in a boolean context, where some values are considered true while others are considered false. Here is how you can do it:

• Truthy values: Values such as a non-empty string, like ‘Hello’ or ‘0’, any non-zero number, like 1,5,-8,.2, or a non-empty array, like 1,2 and 3, resources and objects are considered ‘truthy values’.
• Falsy values: In PHP, values such as the integer 0, float 0.0, boolean ‘false’, empty array [], and null are considered ‘falsy’ values.

Q35. How can you create a FOR() loop in PHP?

Answer: A FOR() loop in PHP is a control structure that enables you to execute a block of code repeatedly for a specified number of iterations. You can create a FOR() loop by inputting the following command:

or($int = 1; $int <= 10; $int++) {
		print("$int<br>");
	}

Tip: To answer such technical PHP developer interview questions, you can try to implement loops for a better understanding of the concept.

Q36. Is PHP strictly typed?

Answer: No, PHP is not a strictly typed language. This means variables in PHP can change during runtime and have no fixed types. This means you can assign a value of one type to a variable and then later assign a value of a different type without any issues.

Q37. How do PHP and HTML interact with each other?

Answer: PHP and HTML interact in the following ways:

• Embedding PHP in HTML: PHP code is embedded directly within HTML using special tags. This enables developers to mix static HTML with dynamic PHP content.
• Dynamic Content Generation: PHP can retrieve data from databases, process it, and generate HTML output based on that data. This helps in creating a list of ‘items’ from a database.
• Form Handling: PHP is also used to process form submissions. When a user submits a form, PHP can handle the data, perform validations, and generate appropriate responses.
• Content Management: PHP allows for the creation of content management systems (CMS) where the HTML structure remains constant while the content can be dynamically updated based on user input or database records.

Q38. What is the main difference between ASP.NET and PHP?

Answer: The main differences between ASP.NET and PHP are as follows:

ASP.NET	PHP
ASP.NET is a web application framework.	PHP is a server side scripting language.
ASP.NET is primarily Window based.	PHP can be used over a wide range of platforms such as macOS, Linux, and Windows.
ASP.NET is generally faster due to its compiled nature.	PHP runs comparatively slower on most occasions.
ASP.NET primarily uses SQL server.	PHP supports a wide range of databases such as PostgreSQL, MySQL, and more.

Q39. Define cookies. How can you create them in PHP?

Answer: Cookies are information stored on the user’s browser by the web server. They are essential in creating a more customized experience for the user. Additionally, they also remember information such as login history, tracking information, and user preference and permission. Cookies retain user-specific data. 

Creating a cookie in PHP involves the following steps:

1. Open your PHP file: Open the PHP file where you want to create your cookie. Go to the beginning of the script, before an HTML output.
2. Use the setcookie() function: Use the setcookie() function to create a cookie. 
3. Define Parameters: Choose the parameters you want to apply to your cookie. This can be the name of the cookie, the value you would like to store, and the cookie’s expiration time. You can also add information about the server’s path where your cookie would be and the domain name. 
4. Access the Cookie: Finally, you can access the cookie by using the $_COOKIE superglobal array. This can be done on the same page or a different page after the cookie is set.
5. Test the Cookie: You can test the cookie by loading the PHP file in your browser. You would either see a greeting text or a message indicating the cookie is not set.
6. Check Cookies in the Browser: If the cookie was created in Chrome, right-click on the page, select ‘Inspect’ and go to the ‘Application’ tab, and check under ‘Cookies’ to ensure your cookie is running.

Q40. How does the PHP spl_autoload_register() function work, and why is it preferable over traditional autoloading methods?

Answer: The spl_autoload_register() lets you define a function that loads classes when they are incorporated. It is preferred over the conventional __autoload() function because it allows you to write the logic to load classes easily and register numerous autoload routines. 

Conclusion

PHP is a complex field; therefore, as a PHP developer, you must have a strong understanding of technical concepts. These sample PHP developer interview questions ranging from fundamental PHP principles to complex programming syntax can help you outline your past working experience and understanding of the programming language. Moreover, interviewers also look for candidates with problem-solving skills. By demonstrating how you have solved complex problems in the past, you can stand out from the crowd. 

To make an impact, you would also need to know the qualifications interviewers are looking for. Our guide on PHP developer job description discusses the key skills and qualifications interviewers look for in a candidate. Make sure to check it out to prepare well!

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