Top 50 Must Know Interview Questions for PHP

Edited By Team Careers360 | Updated on Apr 04, 2024 06:35 PM IST | #Web Development

If you are considering a career in web development, one of the languages you should become familiar with is PHP. Hypertext Preprocessor, or PHP, is a widely used, open-source scripting language designed for web development. It is embedded within HTML and can be used to create dynamic web pages and applications. PHP has been around for more than two decades, and it is still a popular choice for web developers. As such, interview questions for PHP will likely remain relevant in the future.

Top 50 Must Know Interview Questions for PHP

In this blog post, we will cover the top PHP interview questions and answers for freshers as well as experienced professionals. We will look at everything from basics to more complex concepts such as object-oriented programming and security best practices. So, if you seek to increase your chances of landing a job in web development, check out these top interview questions with detailed answers for better preparation.

Q1. How to install PHP?

This is one of the most basic interview questions for PHP. Assuming you have a Windows machine, you can install PHP by following these steps:

Download the PHP Windows zip package from http://www.php.net/downloads.php.
Unzip the package into the directory you want PHP installed in (e.g., C:\PHP).
Add the path to the PHP binaries to your PATH environment variable so that you can run PHP from any command prompt.
Open up the php.ini file in a text editor and set any configuration options you want (e.g., enable error reporting, and set your time zone.).
Restart your web server so that it can load the new PHP configuration.

Q2. How to create a PHP script?

This is another one of the top interview questions for PHP. To create a PHP script, you will need a text editor such as Notepad++ or Sublime Text. Once you have your text editor open, you will need to start each new line of code. In between those two tags, you can add any lines of code that you want. For example, let us say that we want to create a PHP script that prints out the phrase "Hello, world!" on the screen. Here is what our code would look like: echo "Hello, world!"; ?>

Q3. How to run a PHP script?

To run a PHP script, you will need to have a web server that is configured to use the PHP programming language. Once you have a web server up and running, you can create a new file with a .php extension and place your PHP code within this file. After saving the file, you can then access it through your web browser by visiting the URL of the file. If everything is working correctly, you should see the output of your PHP code on the screen. This is amongst the topics that must be included in your PHP interview questions and answers preparation list.

Q4. What is a variable in PHP?

A variable is a value that can be changed during the script. A variable can be a number, a string, or an array. In PHP, variables start with a $ sign followed by the name of the variable. The name of the variable can be anything you want as long as it starts with a letter or an underscore. You must practice for this one of the PHP interview questions and answers for better preparation.

Q5. What are the data types in PHP?

This is one of the common interview questions for PHP. In PHP, there are four main data types: integers, floats, strings, and booleans. Integers are whole numbers that can be positive or negative. Floats are fractional numbers that can also be positive or negative. Strings are a sequence of characters and can be enclosed in single or double quotes. Booleans are true or false values.

Q6: What are PHP namespaces, and how do they help manage code organisation in large projects?

PHP namespaces are a way to organise code by encapsulating classes, functions, and constants within a distinct namespace. They help manage code organisation in large projects by preventing naming conflicts between different parts of the codebase. Namespaces allow developers to define classes or functions with the same name in separate namespaces without conflicts. This ensures that code remains organised, reduces naming clashes, and makes it easier to collaborate on larger projects.

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Q7. What is an object in PHP?

This type of interview questions for PHP are important to practice. An object is a data type that represents a real-world entity. In PHP, an object is a collection of data (variables) and methods (functions) that work together to model a complex system. For example, a car is an object. It has data such as colour, make, model, and year. It also has methods such as drive() and stop().

Q8. What are the control statements in PHP?

There are four control statements in PHP: if, elseif, else, and switch.

If statement: The if statement is used to execute a certain block of code if a condition is true.

If...else statement: The if...else statement is used to execute a certain block of code if a condition is true, and another block of code if the condition is false.

Elseif statement: The elseif statement is used to execute a certain block of code if a condition is true, and another block of code if the condition is false. The elseif statement can be used multiple times.

Switch statement: The switch statement is used to execute a certain block of code depending on the value of a variable.

Q9. What are the functions in PHP?

This type of PHP interview questions and answers are important to practice. PHP is a scripting language that is used to create dynamic web pages. PHP scripts are executed on the server and the results are then passed to the client. PHP is a powerful tool for creating dynamic and interactive web pages. The most common use of PHP is to display data from a database on a web page. PHP has many built-in functions that can be used to perform various tasks. Some of the most commonly used functions are:

echo: This function is used to output data to the screen.
print: This function is also used to output data to the screen. It can be used as a replacement for echo.
die: This function terminates the execution of a script. It can be used to display an error message or redirect the user to another page.
require: This function includes another PHP script in the current script. This allows you to reuse code from other scripts.
include: This function works like required, but does not cause an error if the file does not exist.

Q10: What is the purpose of PHP's "PDO" (PHP Data Objects), and how does it enhance database security?

PHP's "PDO" is an extension that provides a consistent interface for interacting with various database management systems (DBMS). It enhances database security by facilitating the use of prepared statements and parameterized queries, which help prevent SQL injection attacks. "PDO" allows developers to write database queries with placeholders for user input and then bind user-provided values to these placeholders. This approach automatically escapes and sanitizes input, reducing the risk of malicious SQL injection. You must practice for this amongst the top PHP oops interview questions for a better understanding of the topic.

Q11: How does PHP differ from other scripting languages like JavaScript?

PHP is a server-side scripting language, while JavaScript is primarily a client-side scripting language. PHP is executed on the server, generating HTML or other output that is sent to the client's browser for rendering. In contrast, JavaScript runs in the browser, allowing for dynamic client-side interactions. This is one of the must-know PHP interview questions for freshers.

Q12: What is the difference between single quotes ('') and double quotes ("") in PHP when defining strings?

This is one of the must-know PHP basic interview questions for both freshers and experienced professionals. Single quotes ('') in PHP treat everything within them as a literal string, so variables and escape sequences are not interpreted. Double quotes ("") interpret variables and escape sequences within the string. For example, with single quotes: '$var' would be treated as the string "$var," while with double quotes: "$var" would be replaced with the value of the variable $var.

Q13: Explain the purpose of the PHP "echo" statement.

This is one of the frequently asked PHP logical interview questions. The "echo" statement in PHP is used to output text or variables to the web page. It is often used to display dynamic content generated by PHP scripts, such as HTML, text, or the results of calculations.

Q14: What is the use of the PHP "include" and "require" statements?

The "include" and "require" statements in PHP are used to include the contents of another PHP file into the current PHP script. The main difference is that if the "include" statement cannot find the file, it will produce a warning and continue executing the script. On the other hand, the "require" statement will produce a fatal error and stop script execution if the file is not found. This is one of the PHP interview questions for experienced programmers and freshers alike.

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Q15: How can you prevent SQL injection in PHP when working with databases?

This is one of the important PHP OOPs interview questions. To prevent SQL injection in PHP, you should use prepared statements or parameterized queries when interacting with databases. Prepared statements separate SQL code from user input, making it difficult for malicious input to alter the SQL query.

Q16: Explain the concept of PHP sessions and why they are used.

This is amongst the top PHP developer interview questions that must be included in your preparation list. PHP sessions are a way to store user data on the server to persist across multiple requests. Sessions are often used to store user login information, shopping cart contents, or other data that needs to be maintained as a user navigates a website. They are implemented using session variables and are essential for creating interactive and personalised web applications.

Q17: What is the purpose of the PHP function "unset()"?

This is one of the important PHP OOPs interview questions you should practice. The PHP function "unset()" serves the purpose of deallocating a variable, thereby releasing memory resources. It is commonly employed to eliminate a variable's value or erase an element from an array, promoting efficient memory management in PHP scripts.

Q18: How can you pass data from one PHP page to another?

Data can be passed from one PHP page to another using various methods, including:

Using URL parameters: Data can be appended to the URL and accessed using the $_GET superglobal.
Using sessions: Data can be stored in session variables and accessed across multiple pages.
Using cookies: Data can be stored in cookies and retrieved in subsequent requests.
Using HTML forms: Data can be submitted via forms and processed on the target PHP page.

Q19: What is the purpose of the "header()" function in PHP?

This is one of the frequently asked PHP interview questions and answers for freshers as well as experienced professionals. The "header()" function is used to send HTTP headers to the browser. It is often used to perform actions like redirecting the user to a different page or setting cookies. Headers must be sent before any actual output, such as HTML content.

Q20: Explain the concept of PHP namespaces and why they are used.

This is one of the basic PHP interview questions for freshers. PHP namespaces provide a way to organise and encapsulate code to prevent naming conflicts. They are especially useful in larger applications where multiple developers may be working on different parts of the code. Namespaces allow for clearer code organisation and reduce the risk of function or class name clashes.

Q21: What is the use of the PHP "isset()" function, and how does it differ from "empty()"?

The "isset()" function in PHP is one of the must-know topics while preparing for PHP programming interview questions and answers. The "isset()" function in PHP is used to check if a variable is set and not null. It returns true if the variable exists and has a non-null value. In contrast, the "empty()" function checks if a variable is empty, which includes values like an empty string, null, false, 0, or an empty array. "empty()" returns true if the variable is empty, false otherwise.

Q22: How can you handle errors and exceptions in PHP?

In PHP, errors and exceptions are amongst the topics that are frequently asked during interviews, thus, this must be included in your PHP interview questions and answers preparation list. Errors and exceptions can be handled using techniques such as:

Using the "try" and "catch" blocks to catch exceptions and handle them gracefully.
Custom error handling functions using set_error_handler() to define custom error handling behaviour.
Using error_reporting() to set the error reporting level to control which types of errors are displayed or logged.

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Q23: Explain the concept of PHP autoloaders and why they are used.

This is one of the advanced PHP interview questions you should prepare for. PHP autoloaders are functions or methods used to automatically load classes when they are needed, rather than requiring explicit "include" or "require" statements for each class. Autoloaders improve code organisation and make it easier to manage class dependencies in larger projects.

Q24: What is the purpose of the PHP function "array_push()"?

The "array_push()" function in PHP is another one of the topics that must be included in your PHP interview questions and answers preparation list. This function is used to add one or more elements to the end of an array. It takes the array as the first argument and the elements to add as subsequent arguments. The "array_push()" function is commonly used to append values to an existing array.

Q25: Explain the concepts of "GET" and "POST" methods in PHP forms.

This is one of the must-know interview questions for PHP. In PHP, "GET" and "POST" are two methods used to submit form data to a server.

"GET" method appends form data to the URL as query parameters. This method is suitable for data retrieval and should not be used for sensitive data, as the data is visible in the URL.

"POST" method sends form data in the body of the HTTP request. This method is suitable for sensitive data and can handle larger amounts of data.

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Q26: What is a PHP constant, and how is it different from a variable?

This topic must be included in your PHP interview questions and answers preparation list. A PHP constant is a name or an identifier for a simple value that cannot be changed during script execution. Constants are typically used for values that remain constant throughout the script, such as configuration settings. Unlike variables, constants do not have a dollar sign ($) prefix, and they are defined using the "define()" function.

Q27: How can you upload files in PHP using HTML forms?

This is one of the best PHP interview questions for freshers as well as experienced professionals. To upload files in PHP using HTML forms, you need to:

Create an HTML form with the "enctype" attribute set to "multipart/form-data." This attribute is required for file uploads.
Use the "input" element with the "type" attribute set to "file" to create a file input field.
In the PHP script that processes the form, use the $_FILES superglobal to access the uploaded file's information, including its temporary location and name.
Move the uploaded file from its temporary location to the desired destination using functions like "move_uploaded_file()".

Q28: Explain the purpose of the PHP "foreach" loop.

The "foreach" loop in PHP is used to iterate over arrays and objects. It simplifies the process of iterating through each element of an array or each property of an object. It is particularly useful when you want to act on each element without the need for explicit index management. This is one of the most asked interview questions for PHP.

Q29: What is the difference between "array_merge()" and "array_merge_recursive()" in PHP?

If you are preparing for your PHP interview, this is amongst the must-know interview questions for PHP. The "array_merge()" in PHP is used to merge two or more arrays by appending the values of one array to another. If two arrays have the same string keys, the values from the second array will overwrite the values from the first array. "array_merge_recursive()" is used to merge arrays recursively. When two arrays have the same string keys, "array_merge_recursive()" creates an array of values for that key, preserving both values.

Q30: How can you create and use cookies in PHP?

This is one of the important PHP interview questions for experienced professionals. To create and use cookies in PHP, you can use the "setcookie()" function. This function takes several parameters, including the cookie name, value, expiration time, path, and domain. Once a cookie is set, it can be accessed using the $_COOKIE superglobal in subsequent requests. Cookies are often used to store user preferences, session information, or tracking data.

Q31: What is the purpose of the PHP function "count()"?

The PHP function "count()" is a topic that must be practised while preparing for PHP logical interview questions. The PHP function "count()" serves the purpose of determining the quantity of elements within an array or the attributes within an object. It efficiently calculates and returns this count as an integer, facilitating dynamic data manipulation and control in PHP applications.

Q32: Explain the concept of PHP sessions and why they are used.

PHP sessions are a way to store user data on the server to persist across multiple requests. Sessions are often used to store user login information, shopping cart contents, or other data that needs to be maintained as a user navigates a website. They are implemented using session variables and are essential for creating interactive and personalised web applications. For better preparation, you must this one of the interview questions for PHP.

Q33: What is the purpose of the PHP function "file_get_contents()"?

This is one of the advanced PHP interview questions you should practice. The "file_get_contents()" function in PHP is used to read the entire contents of a file into a string. It simplifies the process of reading and working with the contents of files, such as text files or remote resources accessible via URLs.

Q34: Explain the purpose of PHP's "htmlspecialchars()" function and how it contributes to security.

The "htmlspecialchars()" function in PHP is amongst the most asked interview questions for PHP. This function is used to convert potentially dangerous characters in user input, such as HTML tags and special characters like "<" and ">", into their HTML entity equivalents. The "htmlspecialchars()" function is crucial for security because it prevents cross-site scripting (XSS) attacks by ensuring that user-provided data is displayed as plain text rather than being interpreted as HTML or JavaScript. By using "htmlspecialchars()" to sanitise user input before displaying it on a web page, you can significantly reduce the risk of XSS vulnerabilities.

Q35: What is the purpose of the PHP function "header()"?

This is another topic that must be included in your PHP developer interview questions and answers preparation list. The "header()" function in PHP is used to send HTTP headers to the browser. It is often used to perform actions like redirecting the user to a different page, setting cookies, or specifying the content type of the response. Headers must be sent before any actual output, such as HTML content.

Q36: What is Type hinting in PHP?

Type hinting refers to a concept that provides hints to function for the expected data type of arguments. When you write the function, PHP will check whether or not the arguments are of the specified type. If not, the run-time will raise an error and execution will be halted. Type hinting helps users debug the code easily or the code provides errors very specifically. This is another one of the interview questions for PHP you should practice for better preparation.

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Q37: What is the purpose of the PHP function "unlink()"?

This is one of the must-know PHP developer interview questions. The "unlink()" function in PHP serves the purpose of permanently deleting files from the server's file system. By specifying the file path as its argument, it enables the removal of unwanted or temporary files, ensuring they are no longer stored on the server.

Q38: Explain the concept of PHP traits and how they are used.

This is among the most important interview questions for PHP. The PHP traits are a way to reuse and share methods among classes without using multiple inheritance. A trait is a collection of methods that can be used in multiple classes. Classes can use multiple traits to inherit methods and behaviours, allowing for code reuse and improved code organisation.

Q39: What is PHP composer, and why is it used in web development?

PHP Composer is a dependency management tool for PHP that simplifies the process of managing external libraries and packages. It allows developers to define project dependencies in a "composer.json" file and automatically download and install them. Composer is widely used in web development to manage packages and streamline the integration of third-party components into PHP projects. You must practice for this one of the PHP logical interview questions for your next interview.

Q40: How can you optimise the performance of a PHP web application?

This is one of the advanced PHP interview questions. To optimise the performance of a PHP web application, you can:

Use caching mechanisms like opcode caching (e.g., APC or OPcache) to reduce script execution time.
Optimise database queries by indexing tables and using proper SQL queries.
Minimise HTTP requests by combining and minimising CSS and JavaScript files.
Use a content delivery network (CDN) to serve static assets.
Implement server-side caching for dynamic content.
Profile and analyse the code to identify performance bottlenecks and optimise critical sections.

These strategies help improve the speed and efficiency of PHP web applications for better user experiences.

Q41: What is the purpose of the PHP function "array_key_exists()"?

The "array_key_exists()" function in PHP is used to check if a specific key exists within an array. It returns true if the key exists and false otherwise. This function is useful for validating the presence of keys before accessing their corresponding values in an array. This is another one of the interview questions for PHP.

Q42: Explain the difference between the "GET" and "POST" superglobals in PHP.

Amongst the must-know interview questions for PHP is the differences between super global variables of PHP. $_GET is a PHP superglobal used to collect data sent to the server via the URL's query parameters. It is suitable for non-sensitive data and is commonly used for retrieving information. On the other hand, $_POST is another PHP superglobal used to collect data sent to the server via HTTP POST requests. It is more secure and suitable for handling sensitive data, such as login credentials or form submissions.

Q43: What is the purpose of the PHP function "array_unique()"?

This is one of the PHP programming interview questions you must prepare for. The "array_unique()" function in PHP is used to remove duplicate values from an array. It returns a new array containing only the unique values found in the original array, preserving the order of the first occurrence of each value.

Q44: How can you handle file uploads in PHP and ensure security?

To handle file uploads in PHP securely, you should:

Use the "enctype" attribute with the value "multipart/form-data" in the HTML form to enable file uploads.
Validate file types and sizes on the server side to prevent malicious uploads.
Store uploaded files in a directory with appropriate permissions.
Generate unique file names to avoid overwriting existing files.
Implement measures like MIME type verification and file extension checks to ensure uploaded files are safe.

Q45: Explain the purpose of the PHP "try," "catch," and "finally" blocks in exception handling.

This is another one of the important PHP interview questions and answers for freshers and professionals alike. In PHP exception handling, the "try" block is used to enclose code that might throw an exception. The "catch" block is used to catch and handle exceptions that occur within the "try" block. The "finally" block (optional) is used to specify code that runs regardless of whether an exception is thrown or not. It is often used for cleanup tasks.

Q46: What is the difference between "echo" and "print" in PHP?

This type of interview questions for PHP is frequently asked during the interview. "echo" is a language construct in PHP and does not return a value. It is used to output one or more strings and can be used with multiple arguments separated by commas. On the other hand, "print" is a language construct but returns a value (1). It is used to output a single string and does not support multiple arguments.

Q47: What is PHP's "magic_quotes_gpc," and why is it deprecated?

This is amongst the most asked interview questions for PHP. "magic_quotes_gpc" was a PHP feature designed to automatically escape data from GET, POST, and COOKIE variables to protect against SQL injection and other security vulnerabilities. However, it is deprecated as of PHP 5.3 because it led to issues when handling data with certain database systems and caused confusion among developers. Modern PHP applications should use prepared statements or parameterized queries for security instead.

Q48: Explain the purpose of the PHP function "json_encode()" and "json_decode()".

This is another one of the frequently asked interview questions for PHP. "json_encode()" is used to convert a PHP data structure (arrays or objects) into a JSON-encoded string. This is useful for transmitting data to JavaScript or other systems that can parse JSON.

"json_decode()" is used to parse a JSON-encoded string and convert it into a PHP data structure (arrays or objects). It is commonly used to process JSON data received from external sources.

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Q49: What is the difference between "require_once" and "include_once" in PHP?

This is another topic you must include in your PHP interview questions and answers preparation list. "require_once" and "include_once" are used to include external files in PHP. "require_once" includes a file and generates a fatal error if the file is not found or cannot be included. It ensures that the file is included only once, even if called multiple times. "include_once" includes a file but does not generate a fatal error if the file is missing or cannot be included. It also ensures that the file is included only once.

Q50: Explain the concept of PHP closures (anonymous functions) and their use cases.

This is one of the advanced PHP programming interview questions that must be included in your PHP interview questions and answers preparation list. PHP closures, also known as anonymous functions, are functions without a specific name. They can be assigned to variables, passed as arguments to other functions, and used as return values from functions. Closures are useful for tasks like defining callback functions, creating reusable functions on the fly, and implementing concise one-off functions within code.

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Conclusion

PHP is a versatile programming language that can be used to create powerful web applications. To land your dream job in PHP development, you must be well-prepared and know PHP interview questions and answers. We hope this article on interview questions for PHP has made the process easier by providing a comprehensive list of the top PHP interview questions and answers for your next interview.

Frequently Asked Question (FAQs)

1. Is PHP a good career option?

PHP is a widely used programming language and is in high demand by employers. There are a plethora of career options after competing PHP courses including PHP developer, PHP programmer and more.

2. What should I wear for PHP job interviews?

It is always best to dress professionally for a job interview, regardless of the industry or role. For a PHP developer role, you can opt for business casual attire such as a collared shirt, dress pants or a skirt, and closed-toe shoes.

3. What kind of questions can I expect in a job interview for a PHP developer role?

You can be asked technical questions on PHP programming, web development, and database management. Additionally, you may be asked behavioural questions to assess your communication skills, problem-solving abilities, and teamwork experience.

4. What are some important skills and qualifications required for a PHP developer?

Some of the important skills for a PHP developer include a strong understanding of PHP programming, web development frameworks such as Laravel or Symfony, and SQL databases.

5. What qualities should I bring to a job interview for a PHP developer role?

You must possess certain good work qualities including communication skills, confidence, problem solving abilities, initiative, persistence, leadership, creativity, accountability, and professionalism, among others.