Most Popular PHP Interview Questions

PHP is one of the widely used server-side programming languages. PHP is used in approximately 80% of the world's top 10 websites, including Facebook, WordPress, Wikipedia, Etsy, Pinterest, etc.

Are you looking for a job as a PHP developer? One of the first things to do before getting hired as a PHP developer is to prepare yourself for the interview. In this article, we have listed the most common PHP interview questions that hiring companies are likely to ask while testing your knowledge and expertise!

 

Most Popular PHP Interview Questions

 

1. What is PHP?

PHP is an open-source programming language commonly used to create dynamic websites and mobile APIs. It can be used to turn static web pages like HTML, CSS, and JavaScript into dynamic ones. It was developed by Rasmus Lerdorf in 1994.

 

2. What are the advantages of PHP?

1. Easy to learn and use.
2. Flexible and versatile.
3. Widely used on the web.
4. Compatible with many databases and platforms.
5. Open source.
6. A large ecosystem and community support.
7. High performance.
8. Provision of up-to-date and secure versions.

 

3. What are the uses of PHP?

✔️ It is used to design dynamic websites or web applications.

✔️ It takes data from forms to generate dynamic page content.

✔️ It performs operations such as sending and receiving databases, sessions, authentication information, sending emails, etc.

✔️ It is used to add, delete, and modify content in the database.

✔️ It is used to set access restrictions to the user's web page.

 

4. What is PEAR in PHP?

🔄 PEAR is a distribution system for reusable PHP components that includes a library for reusing PHP snippets and code. PEAR stands for PHP Extensions and Applications Repository. It simplifies the use of PHP applications by hosting hundreds of extensions created and distributed by users.

 

 

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

👉 Static Website: In static websites, the content is not processed on the server.

👉 Dynamic Website: Web pages are returned from the server processed during runtime; this means there are no pre-built web pages.

 

 

6. What is the most common way to start and end a PHP code block?

Defining a PHP code block between <?php and ?> is the most common way. The most common way to start and end a PHP code block is shown as follows:

 

7. How to run a PHP script from the command line?

A PHP script can be run from the command line by following these steps: 

1️⃣ Open the terminal or command line window.

2️⃣ For Windows, type "cmd" or "Command Prompt" in the Start menu and press Enter. For MacOS or Linux, open the Terminal application. 

3️⃣ Use the "cd" command to navigate to the directory where the script is located. 

4️⃣ Run the script using PHP command line tools.

 

8. How to display text with a PHP script?

There are two methods to display text: echo and print. PHP tags are used to define the PHP code block. The echo or print command is used to display the text. When the script is run in a web browser, the text will appear on the screen.

 

9. Is PHP a case-sensitive programming language?

No, PHP is a partially case-sensitive language. Variable names are case-sensitive, and function names are not case-sensitive. This means that user-defined functions are not case-sensitive.

 

10. What is the main difference between PHP 4 and PHP 5?

👉 PHP 5 offers better object-oriented programming support. In PHP 4, classes and object definitions are weaker. 

👉 PHP 5 has better performance compared to PHP 4. PHP 5 offers faster execution speed, better error handling, and better XML support. Additionally, PHP 5 includes extra APIs and libraries.

 

11. What are the rules to consider when naming a PHP variable?

• ✅ A variable declared in PHP must start with a dollar sign ($) followed by the variable name. 
• ✅ A variable name can include alphanumeric characters and underscores (e.g., 'a-z', 'A-Z', '0-9', and '_'). 
• ✅ A variable name must start with a letter or an underscore, not a number. 
• ✅ PHP variables are case-sensitive, meaning $sum and $SUM are treated differently.

 

12. What are the types of PHP variables? 

There are 8 data types used to create variables in PHP: 

✔️ Integers - Whole numbers like 2345 

✔️ Doubles - Decimal numbers like 3.14159 or 49.1 

✔️ Booleans - Conditions that can only take two values: true or false 

✔️ NULL - A special type that can only have one value 

✔️ Strings - A variable type that represents text data. “Rain” 

✔️ Arrays - Structures that hold multiple pieces of data in a single variable. 

✔️ Objects - Special data types created by classes 

✔️ Resources - Special variables that contain references to external resources in PHP

 

13. How is a constant defined in PHP?

The define() function is used to create and define the value of a constant. A PHP constant is an identifier whose value cannot be changed over time. Therefore, once a constant is defined, it can never be altered or redefined. 

• ✅ Use define("CONSTANT_NAME", "Constant Value") to define a constant.
• ✅ First, give the constant a name consisting of letters, numbers, underscores, and uppercase letters.
• ✅ Then, determine its constant value.
• ✅ The defined constant can be used with the same value throughout the code. echo CONSTANT_NAME;

 

14. Provide examples of constants in PHP.

1. LINE - Represents the current line number of the file.
2. FILE - Represents the name of the file.
3. FUNCTION - Represents the name of the function.
4. METHOD - Represents the name of the class method.

 

15. What are the popular content management systems (CMS) in PHP?

 

Among these CMS, you can choose the one that best suits your needs:

🎯 WordPress: WordPress is a free, highly popular, and open-source content management system (CMS) framework. 

🎯 Joomla: It is a free and open-source content management system (CMS) used to distribute web content. 

🎯 Magento: It is an open-source e-commerce platform for developing online businesses. 

🎯 Drupal: It is a content management system (CMS) platform developed in PHP and distributed under the GNU (General Public License).

🎯 Shopify: It is a simple and easy-to-use e-commerce platform.

 

16. What are the popular frameworks in PHP?

• Laravel: It is a high-performance, customizable, and flexible PHP framework. CodeIgniter: It is a simple and fast framework used for small to medium-sized projects. 
• Symfony: It is an advanced framework suitable for large projects. 
• CakePHP: It is an easy-to-use and flexible framework.
• CodeIgniter: It is an open-source, easy-to-use, fast framework based on the Model-View-Controller (MVC) design pattern principles.

 

17. How to create single-line and multi-line comments in PHP?

In PHP, there are two types of comments: single-line comments and multi-line comments. 

Single-line comments start with double slashes (//). 

 

Multi-line comments are enclosed within /* comment section */.

 

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

The count() function in PHP is used to count the number of elements in an array. 

 

19. What is the difference between for and foreach loops in PHP?

There are two types of loop counters in PHP: For loop and Foreach loop. 

 

1️⃣ It is considered that the for loop explicitly performs the iteration, while the foreach loop hides the iteration and simplifies it noticeably. 

2️⃣ The performance of the foreach loop is considered better compared to the for loop. Both types of loops have different advantages for different situations, and the appropriate one can be used depending on the scenario.

 

20. How to enable error reporting in PHP?

If you encounter an error, you can use the error_reporting() function. This function provides information about where and why these errors occur. 

 

21. What are the types of errors in PHP?

PHP has various types of errors, but there are basically four main types of errors. ⚠️

1. Parse error or Syntax Error: These are error types caused by syntax errors in PHP code. For example, mismatched opening and closing parentheses, missing or extra parentheses, unclosed parentheses, missing semicolons, etc.
2. Fatal Error: Serious errors that completely halt the execution of PHP code. 
3. Warning: Errors that can prevent the execution of PHP code but do not stop the entire script from running. 
4. Notice Error: Minor error types. This means the program contains something incorrect but allows the script to execute.

 

22. What is inheritance in PHP? Does PHP support multiple inheritance?

Inheritance in PHP is when a property and function of one object are inherited by another object. The extend keyword is used. Also, PHP does not support multiple inheritance.

 

23. What are GET and POST in PHP?

• 1️⃣ GET: GET is a method of sending data. It requests data from a specific source. Data is sent as URL parameters, which are strings consisting of name-value pairs separated by ampersands (&). 
• 2️⃣ POST: POST is a method of sending data. It allows data generated from a user's browser to be sent securely without being displayed in the URL.

 

24. What are the unset() and unlink() functions in PHP?

• 1️⃣ The unlink() function: It is a built-in function used to delete a file in PHP. The function returns True on success and False on failure. 
• 2️⃣ The unset() function: It is used to remove content by emptying it from the file. 

 

25. What is the maximum size of a file that can be uploaded using PHP?

The default maximum upload file size for PHP scripts is set to 128 megabytes. However, this can be changed.

 

26. How to remove line breaks from a string?

Line breaks can be removed from a string using the str_replace() function. 

 

27. What is NULL?

NULL is a special data type that can only have one value. 

NULL can be assigned as follows 👇: 

 

By default, NULL is written in uppercase. However, it is actually case-insensitive, meaning it can also be written as follows 👇:

 

28. What is the purpose of the constant() function?

The constant() function is a PHP function that returns the value of a constant corresponding to a given constant name. 

 

29. What are the two most common ways to start and end a PHP code block?

 

1️⃣

 

2️⃣

 

 

30. What are constructors and destructors in PHP?

Constructors and destructors are special types of functions in PHP classes that are automatically called when a class object is created and destroyed. 

👉 Constructor: It is used to perform tasks such as initializing the class and assigning initial values to its properties. 

👉 Destructor: It is used to perform tasks such as freeing resources (e.g., file connections or database connections). 

 

 

31. How to use sessions and cookies in PHP?

A session is a global variable stored on the server. Sessions have a relatively large capacity for storing data compared to authentication information. Session values are automatically deleted when the browser is closed.

A session in PHP is started as follows 👇:

 

A cookie in PHP is created as follows 👇: