Top PHP Interview Questions (with Answers)

By | January 12, 2022
PHP Interview Questions

PHP is a scripting language that is easy to learn and simple to use for all levels of programmers. In general, PHP is a programming language suitable for back-end or server-side web development. Also, PHP has a large community that is ready to help PHP developers with their issues. So let’s discuss the most commonly asked PHP interview questions.

There are so many big web apps and online platforms that are using PHP, including Facebook, Wikipedia, WordPress, and Slack. Thus, there are several opportunities in building a career in PHP development. However, to join any big company as a PHP developer, you must have to face an interview.

Usually, while appearing for an interview, the interviewer will check your conceptual knowledge about PHP. Thus, to give your best, you must prepare yourself for the interview. To help you with that, we have curated a list of the most frequently asked interview questions for PHP along with their appropriate and detailed answers.

So, without any more delay, let’s start discussing the most popular PHP interview questions.

Top PHP Interview Questions and Answers

Here are the top PHP interview questions and answers that can help you prepare better for your upcoming interview.

1. What is PHP?

Answer: PHP, also known as Hypertext Preprocessor, is a general-purpose, open-source, scripting language for web development that runs on the server-side. PHP scripts are dynamically-typed and facilitate the creation of dynamic web pages efficiently and quickly. Also, PHP is completely free to download and use. Its syntax is inspired by some object-oriented programming languages, such as Java and Perl.

2. What is the full form of PHP?

Answer: The full form of PHP is Hypertext Preprocessor.

Vamware

3. What does PEAR stand for?

Answer: PEAR is an acronym for PHP Extension and Application Repository. It extends PHP to provide a higher level of programming for web developers. PEAR also offers a CLI (Command Line Interface) that allows automatic installation of “packages”.

4. Which programming language does PHP resemble?

Answer: PHP syntax is derived from Perl and C programming languages.

5. What are the differences between PHP & Java?

Answer:

PHP Java
It is a server-side scripting language. It is a high-level general-purpose programming language.
PHP is dynamically-typed. Java is statically-typed.
It doesn’t have a rich set of APIs. It supports a rich set of APIs.

6. What is the latest version of PHP?

Answer: The latest version of PHP is PHP 8.1. which was released in November 2021.

7. Which version of PHP is most popular?

Answer: Version 7.1 or 7.2 is the most popular version of PHP.

8. What is the command to execute a PHP script from the command line?

Answer: You can use the PHP command-line interface (CLI) and write the exact file name with the .php extension preceded by php execute it. Following is an example command to run a PHP file named script.

php script.php

9. Which function is used to encrypt the password in PHP?

Answer: To create a password with one-way encryption, we can use the crypt () function. This function is defined as crypt (input_string, salt), where input_string is the string that has to be encrypted and salt represents an optional parameter.

Below is a sample code for encrypting the string “techgeekbuzz”:

<?php
$password = crypt('techgeekbuzz');
print $password . "is the encrypted version of techgeekbuzz";
?>

10. Write a Hello World program using a variable?

Answer:

<html>
<head><title>Hello World Script using Variable</title></head>
<body>
<?php
$salutation = “Hello World!”;
echo “<p>$salutation</p>”;
?>
</body>
</html>

11. Define the Zend Engine?

Answer:

  • Zend Engine is a runtime engine and compiler that PHP uses internally. Zend has opcodes that are executed to generate HTML code which is sent to the client. PHP Scripts are loaded into memory and compiled into opcodes.
  • The Zend Engine provides many features such as memory and resource management and many other standard services for the PHP language. Reliability, high performance, and extensibility are key contributors to the increasing popularity of PHP.

12. Write the command to run the interactive PHP shell from the CLI (command-line interface)?

Answer:

The following command runs the interactive PHP shell:

php -a

13. How to display the output directly to the browser with the use of PHP?

Answer: We can use the special tags <?= and ?> to display the output directly to the browser.

14. Does PHP supports multiple inheritances or not?

Answer: No, PHP supports only single inheritance, and it allows the use of one single class to extend a class using the keyword ‘extended.

15. Highlight the main difference between PHP 4 and PHP 5?

Answer: PHP 5 offers additional features of OOP (Object Oriented Programming) compared to PHP 4.

16. What do you understand about a final class and a final method?

Answer: The ‘final’ keyword is introduced in PHP5.

A final class cannot be extended and a final method cannot be overridden.

17. Define echo vs print statement.

Answer:

  • echo() and print() are language constructs in PHP, which are used for output strings. The speed of both statements is almost the same.
  • print() cannot take multiple expressions, whereas echo() can take multiple expressions.
  • print() returns true or false which means success or failure, whereas echo() doesn’t return true or false.

18. What are the different types of errors in PHP?

Answer: Warnings, Notices, and Fatal errors are the different types of errors in PHP. Here’s a brief overview of each error type:

  • Warnings

Warnings occur when calling include() a file, which does not exist. By default, errors are displayed to the user.

  • Notices

Notices are for non-critical errors. For example, accessing a variable that has not yet been defined. These types of small errors are not displayed to the user by default, however, you can change this default behavior.

  • Fatal errors

Fatal errors are critical errors. For example, calling a non-existent class or function. These errors cause the immediate termination of the script.

19. What is the htmlentities function?

Answer: The htmlentities() function is used to convert characters to HTML entities.

20. How PHP and HTML are connected with each other?

Answer: HTML can be generated through PHP scripts, and it is also possible to pass pieces of information from HTML to PHP.

21. Which operator is used to compare the objects in PHP?

Answer: The ‘==’ operator is used to test if two objects are instanced from the same class with the same attributes and equal values. If two objects are referring to the same instance of the same class, we can test it by using the identity operator ‘===’.

22. What library is used for pdf in PHP?

Answer: The PDFlib library Version 6 is used for the PDF functions in PHP to create PDF files. Also, there is FPDF, which is a PHP class that allows the generation of PDF files with pure PHP (without using the PDFlib library). FPDF stands for Free PDF, and you can modify it as per your needs.

23. What are the new features in PHP7?

Answer:

There are several new features in PHP7 that are as follows:

  • Improved performance of Zend Engine 3
  • 64-bit integer support on Windows
  • AST-based compilation process
  • Newly added Closure::call()
  • Declarations of the return type
  • Unicode codepoint escape syntax
  • integer, float, string, and boolean declarations.

24. Which type of operation is required to pass the values through a form or an URL?

Answer: To pass values through a form or an URL, we need to encode and decode them using htmlspecialchars() and urlencode() functions.

25. What is the full form and meaning of MIME?

Answer: MIME stands for Multi-purpose Internet Mail Extensions. It is the standard way of classifying file types over the internet. MIME has two parts, namely type and subtype, and they are separated by a slash (/).

26. How to execute a PHP script using the command line?

Answer: SAPI (Server Application Programming Interface) is used to execute a PHP script. By using the SAPI command, the PHP code can be passed to execute directly.

Ex.:

Php –r ‘print_r(get_defined_constanrs());’

In a shell, PHP –v will display whether the SAPI is CLI or CGI.

27. Explain the htaccess and its use?

Answer: htaccess files are configuration files of Apache Server. These files provide a way to make configuration changes on a per-directory basis. Also, the .htaccess files are used to change the features and functionality of the Apache webserver. Here are some key highlights of an htaccess file:

  • htaccess file is used for URL rewrite.
  • htaccess file can restrict some IP addresses.
  • It can protect the site password; on the restricted IP addresses, the site will not open.

28. How to use image function in PHP?

Answer: A library named GD library is used to execute image functions.

29. What is meant by PEAR in PHP?

Answer: PEAR stands for “PHP Extension and Application Repository”. Following are the key highlights of PEAR:

  • PEAR is a system to use for package maintenance and code distribution.
  • It is a structured library with open-sourced code for PHP users.
  • It offers a different style for writing PHP code.

30. What’s the output buffering in PHP?

Answer: Output buffering in PHP is used to buffer a script’s output. This buffer executes before returning it to the client. Sending to output is by choice because output buffers are stackable.

31. Explain the session in PHP.

Answer: Whenever a new user logs in to an application, they must enter the details that are usually stored in a session variable. This detail is then available to all pages in one application. PHP Sessions work using a unique id for each visitor.

32. How to display text using a PHP script?

Answer: Two methods are available to display a text:

<!--?php echo "Method 1"; print "Method 2"; ?-->

33. How to find the number of days between two given dates in PHP?

Answer: You can use the code as shown below to find the start date and end date

$date2= strotime($end_date);
$date_diff = (($date1)- ($date2)) / (60*60*24)

34. What is Memcache?

Answer: Memcache is a technology that is used to cache objects in memory to increase the speed of your web application so that they can get to them fast. It is used by sites such as NowPublic.com, Digg.com, and Facebook.com. Also, it is widely recognized as an essential ingredient in scaling any LAMP-based app.

35. Give the statements that are used to connect PHP and MySQL.

Answer: Below statements are used to connect PHP with MySQL:

<?
$conn = mysql_connect('localhost');
echo $conn;
?>

This statement gives the resource of the localhost. Other different ways to connect to the database and are as follows:

<?
mysql_connect('db.domain.com:33306','root','user');
mysql_connect('localhost:/tmp/mysql.sock');
mysql_connect('localhost','rasmus','foobar',
true,MYSQL_CLIENT_SSL|MYSQL_CLIENT_COMPRESS);
?>

36. How can we execute a PHP script using the command line?

Answer: Open the PHP CLI (Command Line Interface) program and write the PHP script file name.

For example, “php myScript.php”, “PHP” is the command to invoke the CLI program.

Note– If your PHP script is written for the Web CGI interface, it may not execute in the command line environment.

37. Highlight the differences between the $message and $$message?

Answer:

  • $$message can be used to store the variable of a variable, while $message is used to store variable data.
  • Data stored in the $$message can be changed dynamically, while data stored in the $message is fixed.
  • $$message is a variable of another variable and $message is a variable.

Example

$Message = "YOU";
$you= "Me";
echo $message //Output:- you
echo $$message //output :-Me

38. Why PHP is called a Scripting language?

Answer: PHP is a scripting language, which is used to write scripts. Scripts are files that consist of a set of instructions. Scripts are used to tell the computer to execute the file and print the output on the screen.

39. How to display information of a variable that is readable by a human in PHP?

Answer: We use print_r() to display a human-readable result.

40. Highlight the difference between PHP and JavaScript?

Answer: PHP is a server-side scripting language, which means that it is not allowed to interact directly with the user.

On the other hand, JavaScript is a client-side scripting language, that makes it possible to directly interact with the user.

41. What is the use of ODBC in PHP?

Answer: ODBC stands for “Open Database connectivity”, which allows a user to communicate with other databases like IBM DB2 and Access. PHP supports many databases, like Microsft SQL Server, dBase, Oracle, etc. Other databases like filePro, FrontBase, and InterBase can be used with ODBC connectivity.

42. What is the use of the function file_get_contents()?

Answer: Function file_get_contents() is used to read a file and store it in a string variable.

43. What’s difference between require(), require_once(), and include()?

Answer:

  • require() is used to include and evaluate a specific file. If the file is not found, it gives a Fatal Error.
  • require_once() only includes the file which is being included once. It is recommended for the files where you have lots of functions stored.
  • include() is used to include the file, and if the file is not found, it gives a warning to the user.

44. PHP is an open-source language, therefore is there any support available to use it?

Answer: PHP is an open-source language, and there is a vast community of developers and programmers to support it.

45. How to run PHP?

Answer: Following are the steps to run PHP:

  • Set up the web environment.
  • Set up the web servers. The most used web server for PHP is Apache. Also, one can use IIS (Internet information server) server offered by Microsoft.
  • Install the web server and PHP.
  • Update and administer the system for changes.

46. What is the function which gives us the number of affected entries by a query?

Answer: mysqli_affected_rows() return the number of entries affected by an SQL query.

47. What is the difference between echo, print, and printf()?

Answer:

  • echo is used to print out a string and it shows the content of the message written.
  • print is a construct, it returns TRUE and FALSE.
  • printf() is a function that allows the string output to be formatted. It is the slowest medium to print the data out.

48. How to check whether the value of a given variable is a number?

Answer: The function is_numeric() is used to check whether the value of a variable is a number or not.

49. What is the use of the unlink() function?

Answer: The unlink() function is for file system handling. It deletes the file given as an entry.

50. Why IDE is recommended for PHP development?

Answer: IDE (Integrated Development Environment) is a software program that combines several development tools and makes them readily accessible for one single UI. An IDE can be used for:

  • Debugging
  • Preview
  • Testing
  • FTP
  • Version control

51. What is the difference between a PHP statement and a PHP script?

Answer: PHP statements are a set of instructions that tells PHP to perform an action. On the other hand, a PHP script consists of a series of PHP statements that is used for execution.

Example:

PHP statement: echo “Hi”;
PHP script:
if (time = midnight)
{
put on pajamas;
brush teeth;
go to bed;
}

Conclusion

The PHP interview questions mentioned above cover several important concepts of PHP that interviewers usually ask about. Also, during a PHP interview, the interviewer may give you a problem and ask you to write code, so it’s important for you to learn the PHP syntax. Keep in mind that whether you are a beginner or a professional PHP developer,  you need to make sure that you go through all the PHP basics before you appear in an interview.

If you have any suggestions related to PHP interview questions, feel free to comment them down below.

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Author: Paridhi Joshi

Paridhi Joshi is an expert web content manager with significant experience in content creation. Professionally she is dedicated to staying up to date with the latest trends and technologies in content writing and committed to bringing state-of-the-art web approaches to the workplace. She is an efficient multi-tasker who can complete multiple projects under strict deadlines.

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