30+ PHP Interview Questions [Most Frequently Asked]

PHP: Hypertext Preprocessor is a leading programming language that powers the backend of websites. It is a powerful web scripting language that has been ruling the world of web development for over 2 decades.

There are lucrative working opportunities available for PHP developers. As such, there is also no scarcity of learning material. Among other modes of learning, PHP interview questions is a great option.

Here, in this blog post, we will look into some of the most frequently asked basic and advanced PHP interview questions. So, let’s march on!

Most Popular PHP Interview Questions

Basic PHP Interview Questions

1. What is PHP?

PHP is also known as Hypertext Preprocessor. It is a popular server-side scripting language that is open source and used for web development.

2. What do you mean by PEAR in PHP?

PHP Extension and Application Repository, or PEAR, is what it stands for. It is a framework and acting repository that has all of the reusable PHP parts. It offers you a straightforward interface to automatically install packages and includes some of the PHP libraries.

3. Is PHP a case-sensitive language?

It is possible to think about PHP as a partially case-sensitive language. The names of functions are not case-sensitive, whereas the names of variables are. Additionally, the language as a whole is case-sensitive, although user-defined functions are not.

4. What are the rules for defining a PHP variable?

Some of the rules that must be followed to name a PHP variable are

• The variable must start with a letter or underscore( _ ).
• A variable should not contain spaces.
• A variable must begin with a dollar sign ($) and then have a name. Example: $rollno=21, where rollno is the name of a variable.
• Variables are case-sensitive. For example, $Rollno and $rollno will be considered two different variables.
• The characters in a variable name can be letters, digits, or underscores. However, you cannot use symbols like +, -, %, &, etc.

5. What is a session in PHP?

A PHP session is a method for storing data that can be used across numerous pages of an entire website. In contrast to cookies, the data is not kept on the user’s machine. The session will produce a file on the server that stores the values of registered session variables in a temporary directory. All pages on the website will have access to this information during that visit.

When using an application, you open it, make necessary changes, and close it. This is very similar to a session. You are recognized by the computer. It is aware of when you launch and shut off an application.

On the internet, however, the webserver is unaware of your identity or your occupation because an HTTP address does not keep a state. Session variables are used to solve this issue by storing user data across several pages.

All pages in the same application can access the data stored in session variables, which pertain to a single user.

6. What do you understand by NULL in PHP?

In PHP, the special data type NULL is used to indicate the presence of solely the NULL value. It cannot have any other value assigned to it.

There are two ways to declare null:

• $var=null;
• $var=NULL;

NULL is not case-sensitive so both ways can work fine.

7. How to define constant in PHP?

define() function is used to define constants in PHP. The constant values can be simply defined and obtained with this function. Constants are immutable after definition, as their name suggests. They don’t need the standard PHP syntax, which begins with the $ sign.

8. What are different pre-defined constants in PHP?

Some of the commonly used pre-defined constants that are available in PHP are

• _CLASS_ – used for returning class names.
• _FUNCTION_- used for denoting function name.
• _LINE_ – denotes the working line number.
• _FILE_ –  represents the file name and path of the file.

9. What do you understand by the phrase ‘PHP escape’?

PHP escape is a way for informing the PHP parser that specific code components are not part of the PHP code. This offers the fundamental tools for setting apart a section of PHP code from the rest of the application.

10. Differentiate between constants and variables in PHP?

Intermediate PHP Interview Questions

11. How does PHP handle object comparison?

When determining whether two objects are instances of the same class, possessing the same characteristics, and having the same values, we utilize the operator “==.” With the identity operator “===,” we may determine whether two objects are referring to the same instance of the same class.

12. What is the main difference between require() and require_once()?

The only difference between require once() and require() is that the latter function checks to see if the PHP script has previously been included before executing it.

13. How to display text with a PHP script?

There are two methods to display text with PHP script and those are:

• <!–?php echo “Hello world”; ?–>
• <!–?php print “Hello world”; ?–>

14. How can we use PHP to display information from a variable that is readable by humans?

To display output in a human-readable format one should use print_r().

15. How may a PHP script’s execution time be set to infinite?

To prevent the PHP error “maximum execution time exceeded,” a set time limit(0) is introduced at the beginning of a script. This sets the time of execution to infinite. This can also be specified in the php.ini file.

16. Do PHP and HTML interact?

Yes, the fundamental component that defines PHP is the interplay between HTML and PHP. PHP scripts can simply shift information around and generate HTML mode.

HTML is a client-side language, whereas PHP is a server-side language. By combining the strengths of the two languages, this engagement helps close gaps.

17. What kinds of arrays does PHP support?

PHP uses three main types of arrays:

• Associative Array: As an index, it makes reference to an array of strings. This saves element values along with key values rather than keeping them in a strict linear index order.
• Indexed Array: It refers to an array with an index that is a number. Values are kept and used in a linear way.
• Multidimensional Array: These are arrays with several dimensions and indexes.

18. Explain the working of the foreach loop in PHP.

In order to traverse and loop across the array, PHP uses the foreach statement, which is a looping construct. Foreach operates in a straightforward manner; pointers are increased and elements are allocated values with each iteration of the value. Until the array is finished, this operation is repeated.

Syntax:

foreach(array){
Code

}

19. Why are constructors and destructors used in PHP?

In PHP, constructors are utilized because they make it simple to pass parameters when building new objects. This is done to set the variables for the specific item under consideration.

An object can be destroyed using destructors. These two unique approaches are offered by PHP so that you can complete complicated processes in a single step.

20. What purpose do PHP’s $message and $$message serve?

In PHP, there are two variables: $message and $$message. The name is what makes the difference. While $message has a fixed name, $$message has a variable name that is actually recorded in $message.

For example:

If ‘var’ makes up $message, then $$message is simply ‘$var’.

21. Define the main types of errors in PHP.

The four main types of errors in PHP are as follows:

• Syntax/Parse error: It is the kind of mistake the programmer made in the program’s source code. Non-closed quotes, additional parentheses, non-closed braces, a missing semicolon, etc. can all result in parse issues.
• Notice: These are non-critical mistakes that could happen while the script is running. Users are unable to see these. An example of a “Notice” is accessing a variable that is not defined.
• Warnings: Even though they are more serious than Notices, Warnings don’t stop the script from running. The user can see these by default. Take the example to include() a nonexistent file.
• Fatal: This is the most serious error kind, and when it occurs, the script execution is instantly stopped. This error type manifests itself, for instance, while attempting to access a property of a non-existent object or calling require() on a non-existent file.

22. What exactly is a PSR standard? What does it matter?

Because different developers and businesses have different coding standards, it might be challenging to fix another developer’s code because it may have a different structure. A PSR standard can help with that. It establishes a standard for how the code should appear, which sometimes helps to get rid of problems and even syntax errors.

23. Explain the difference between for and foreach loop.

• While the foreach loop hides the iteration and is obviously more simple, the for loop is thought to be openly conducting the iteration.
• Although the foreach loop iterates over an array of elements, its execution is more straightforward and it completes the loop faster than the for loop.
• For each iteration of the index, the foreach loop allocates temporary memory, which degrades the system’s overall memory allocation efficiency.

24. What is the difference between GET and POST?

GET – In this method data is requested from a specific resource. This approach sends the data as URL parameters, which are typically strings of name-value pairs separated by &.

Syntax:

<?php

$_GET[‘variablename’];

?>

POST – This approach involves communicating separately with the processing script and sending the data to the server as a package. POST method data will not be displayed in the URL.

Syntax:

<?php

$_POST[‘variablename’];

?>

Advanced PHP Interview Questions

25. What is the difference between the unset() and unlink() functions?

Unset() – PHP includes a built-in method called Unset() that can be used to empty a file of all of its content. It means that rather than destroying a file, the function clears its contents. The unset() method accepts a single input variable and clears the contents of the file in addition to unsetting a variable and emptying it.

Unlink() – An in-built PHP method called unlink() is used to remove files from the system. The function takes a filename as an input and outputs True or False depending on whether the operation was successful or unsuccessful. Filename and context are two of the parameters that the unlink() method in PHP accepts.

26. Explain the behavior of the spaceship operator.

“<=>” stands for the spaceship operator, also known as the combined comparison operator. This operator performs comparisons between two operands in three different ways: greater than, less than, and equal. This operator returns:

• 0 if values on both sides are equal
• 1 if the value on the left side is greater
• -1 if the value on the right side is greater

27. Explain urlencode() and urldecode() functions.

urlencode() – A built-in method in PHP called urlencode() is used to encode URLs. With the exception of -_. which is substituted by the percent (%) sign, two hex digits, and spaces encoded as plus (+) signs, this function outputs a string that is entirely non-alphanumeric.

urldecode() – The URL that has been encoded by the encoded() method is decoded using the built-in PHP function urldecode().

28. Explain the differences between runtime exceptions and compile-time exceptions in PHP.

Compile-time exceptions are what they sound like: they happen when a script is being built, during the compilation process. A nice illustration of a compile-time exception is the FileNotFoundException while a runtime exception is one that prevents the script from continuing to execute. An illustration of a runtime exception is the ArrayIndexOutOfBoundException.

29. What do you understand by type hinting in PHP?

In PHP, type hinting is employed when it is necessary to define the data type of an argument before passing it to a function.

The first time this method is used, PHP will quickly check to see if all the requested data types are present. If the result is different, the runtime will halt and an exception will be thrown.

30. What are sessions and cookies in PHP?

The architecture stores sessions, which are global variables, on the server. An individual server ID is assigned to each session, which is later used to handle the storage and retrieval of values.

In the architecture, cookies are utilized as entities to identify certain users. The client system receives a tiny file from the server. This is done in order to collect valuable client feedback that will help the server progress in a number of different areas.

31. What is the difference between echo and print?

32. What are traits?

In languages like PHP and others that do not provide multiple inheritances, traits provide a technique for creating reusable code. It cannot be instantiated by itself.

Through the free reuse of method sets across many independent classes with various class hierarchies, a trait enables developers to overcome the drawbacks of single inheritance.

33. What functions are used to get image properties like size, width, and height?

The functions which are used to get image properties are

• getimagesize – to get the size of the image
• imagesx – to get the width of the image
• imagesy – to get the height of the image

34. How can we make sure a given variable’s value is a number?

To confirm if the variable’s value is a number or not you can use the is_numeric() function.

35. How can we make sure a given variable’s value is alphanumeric?

To confirm if the variable’s value is an alphanumeric or not you can use the ctype_alum function.

Conclusion

There are multiple ways of learning PHP. In addition to learning the popular programming language with PHP books, tutorials, and courses, these interview questions will help you to learn the concepts better. Moreover, you can use these questions to assess your interview readiness.

Aditya Thakur

Aditya is a seasoned JavaScript developer with extensive experience in MEAN stack development. He also has solid knowledge of various programming tools and technologies, including .NET and Java. His hobbies include reading comics, playing games, and camping.