Are you planning to start your career as a PHP developer? Great — you've decided to work with a programming language that powers nearly 80% of the world's top 10 websites, including Facebook, WordPress, Wikipedia, Etsy, Pinterest, and so on.
Interestingly, it's one of the most widely-used server-side languages and has been so for the past 25 years. Despite its long-term history, the demand for PHP hasn't dwindled. Per the U.S. Board of Labor Statistics, there will be a 15% increase in web development positions — including PHP positions — by 2026.
That said, one of the first things to do before you can land a job as a PHP developer is to prepare yourself for the interview. To this end, we've compiled a list of top PHP interview questions that hiring companies are likely to ask while testing your knowledge and expertise.
Of course, that's not all. You will be tested on various other grounds such as general aptitude, management, and communication skills. So if you would like to know more about what it takes to break into this career, check out our in-depth guide on how to become a PHP developer.
The PHP interview questions and answers we’re about to discuss are approved by our PHP Certification Training experts and will come in handy for beginners as well as those looking to upgrade their skills. So let’s not wait anymore and dive right in.
For the sake of clarity and convenience, we’ll divide the list of questions into three parts:
- Beginner PHP interview questions
- Intermediate PHP interview questions
- Advanced PHP interview questions
Beginner-Level PHP Interview Questions
Let us now begin with the basic PHP interview questions and answers.
1. Who do we know as the father of PHP?
Rasmus Lerdorf who created the language in 1994.
2. What did the acronym PHP originally stand for?
Initially, PHP stood for Personal Home Page, but it now stands for the recursive acronym for PHP: Hypertext Preprocessor.
3. What are some of the common applications of PHP?
PHP is commonly used to perform −
- system functions. It can create, open, read, write, and close to files on a system.
- handling forms. It can help. Collect data from files, save data to a file, send data through email, return data to the user, etc.
- tasks that involve adding, deleting, and modify elements within your database
- accessing cookies variables and set cookies.
- user restriction to access some pages of your website
- data encryption
4. What is the recommended PHP version?
The latest versions of PHP are 7.2.30, 7.3.17, and 7.4.5, which was released in April 2020
5. Which programming language is PHP similar to?
PHP is influenced by Perl and C. As such, PHP syntax resembles these languages.
6. What is the PHP scripting engine called?
PHP is powered by the scripting engine Zend Engine 2.
7. What is the main difference between PHP4 and PHP5?
PHP4 uses Zend Engine 1 and doesn't support the OOPs concept, while PHP5 supports the OOPs concept and uses Zend Engine 2.
8. Is PHP a case sensitive language?
Not fully. PHP is partly a case sensitive language where the variable names are case-sensitive but function names are not. Also, user-defined functions aren’t case sensitive but the rest of the language is.
9. What are the popular frameworks in PHP?
Some popular PHP frameworks are:
- Zend Framework
- Yii 2
10. Name the popular Content Management Systems (CMS) in PHP.
Intermediate-Level PHP Interview Questions
Let us now go through the intermediate PHP interview questions and answers.
11. How can PHP interact with HTML?
PHP is designed to interact with HTML. It’s possible to embed PHP scripts in an HTML page without a problem and transfer information from HTML to PHP.
12. How can you embed PHP code in an HTML page?
When embedding PHP code with an HTML file, we must use the .php file extension for that file. This allows your webserver to send the file to PHP for processing. If the webserver is configured to use a different extension for PHP files, that extension must be used instead.
We need to use PHP start and end tags to tell the web server where the PHP code starts and ends. There are three styles of start and end tags that PHP parser recognizes.
- XML style – Mostly used when when merging PHP with XML or HTML documents
- Short style – This is the simplest type, though it is not recommended to avoid interference with XML document declarations.
PHP code goes here
14. Name the different types of variables in PHP.
There are eight data types used to construct variables in PHP −
- Integers − these are whole numbers without a decimal point, like 4195.
- Doubles − are floating-point numbers, like 3.14159 or 49.1.
- Booleans – come with only possible values of either true or false.
- NULL − is a special type with only one value: NULL.
- Strings − are sequences of characters.
- Arrays − are named and indexed set of other values.
- Objects − are f programmer-defined classes, which can include both other kinds of values and functions that are specific to the class.
- Resources − are special variables that refer to resources external to PHP (such as database connections).
15. List the main types of errors in PHP and explain their differences.
There are three main error types in PHP:
- Notices. These are non-critical errors that can occur during the script execution. These are not visible to users. Accessing an undefined variable is an example of a 'Notice'.
- Warnings. These are more critical than Notices, but just like them, Warnings don't interrupt the script execution. However, these are visible to the user by default. Example: include() a file that doesn't exist.
- Fatal. This is the most critical error type which, when occurs, immediately terminates the script execution. Accessing a property of a non-existent object or require() a non-existent file is an example of this error type
16. What are 'Traits'?
A mechanism that lets you create reusable code in PHP and similar languages where multiple inheritances are not supported is called Traits. It's not possible to instantiate it on its own.
17. Can the value of a constant change during the script’s execution?
No, the value of a constant cannot be changed once it’s declared during the PHP execution.
18. Name and define the three scope levels available in PHP.
- Private – Detectable only in its own class
- Public – Can be seen by any other code accessing the class
- Protected – Can be seen by classes parent(s) and classes that extend the current class
19. What do we mean by ‘escaping to PHP’?
The PHP parsing engine must be able to distinguish PHP code from other page elements. The mechanism to achieve this is called ‘escaping to PHP’.
20. How many types of an array are there in PHP?
Three types of an array are present in PHP:
- Indexed array, which is an array with a numeric key.
- An associative array is where each key has its specific value.
- A multidimensional array contains one or more arrays within itself.
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21. What do we mean by a PSR standard? What is its importance?
Because varying coding standards exist between developers and companies, one may run into problems when trying to fix another developer’s code which might have a different structure. That’s where a PSR standard comes in. It standardizes how the code should look, which helps eliminate issues and even syntax errors in some cases.
Advanced-Level PHP interview questions
We will now look into some of the advanced PHP interview questions and answers.
22. What is the use of the function' imagetypes()'?
The imagetypes() function is an inbuilt PHP function which is used to give the image types supported by the current version of PHP inbuilt installed library.
23. What is needed to be able to use the image function?
GD library, which is the inbuilt installed library in PHP, is needed to execute image functions.
24. How do you handle failures in execution with include() and require() functions?
If the function requires () fails to access the file, then it ends with a 'fatal' error. However, in case of the include() function, it gives a warning, and the PHP script continues to run.
25. What is the main difference between require() and require_once()?
require(), and require_once() basically perform the same task. The difference is that the latter checks whether the PHP script is already included or not before executing it.
26. What is the primary difference between include_once() and include()?
Same as above.
27. How do you display text with a PHP script?
There are two ways to do this:
<!--?php echo "Method 1"; print "Method 2"; ?-->
28. How do we use PHP to display information of a variable that's readable by a human?
To achieve this result, we need to use print_r().
29. How do we set an infinite execution time for PHP script?
We add a set_time_limit(0) at the start of a script to make the time of execution infinite. This helps to prevent the PHP error of 'maximum execution time exceeded.' We can also specify this in the php.ini file.
30. Explain the PHP error 'Parse error in PHP - unexpected T_variable at line x'.
This is a syntax error in PHP which tells us that a mistake at the line x stops parsing and executing the program.
31. How to export data into an Excel file?
Commonly, the data is obtained in a format supported by Excel. For instance, we can write a .csv file, select a separator between fields (a comma for example), and then proceed to open the file with Excel.
32. How to execute a PHP script from the command line?
To execute a PHP script, we can use the PHP Command Line Interface (CLI) and specify the file name of the script in this way:
These were some of the common PHP interview questions that hiring companies are most likely to ask during their interview process. We hope these PHP interview questions for freshers as well as professionals will help you regardless of whether you’re about to start your PHP career or are ready to take it to the next level.
If you’re serious about a PHP development career and want to answer your PHP interview questions more confidently, you’d want to master this language and get more in-depth answers to these questions. As such, getting an industry-standard PHP development training will steer you in the right direction.
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