PHP is an older scripting language (it made its debut in 1994) that’s utilized in many web-based services. Its latest version, 8.3, was released in November 2023, with another update due this November. If you’re interested in building web apps, knowing how PHP works can come in useful—and if you apply for any kind of web-related job, chances are good you could face some questions about your PHP knowledge.

If you’re about to apply for a PHP developer job, keep these things in mind as you prep:

• Brush up on fundamentals: Revisit core PHP concepts like object-oriented programming, working with databases, and security best practices.
• Practice your problem-solving skills: Be prepared to tackle coding challenges that assess your ability to think critically and translate requirements into functional code.
• Research the company and role: Tailor your responses to highlight how your skills and experience align with the specific project needs and the company culture.
• Showcase your passion: Let your enthusiasm for PHP shine through!

With all that in mind, here are some PHP interview questions (with responses) you might face:

“How would you find a specific string of text in a batch of files?”

Potential answer: “That’s simple. I'd probably use something like ‘opendir’ or ‘readdir’ to loop though the files and ‘file_get_contents’ to get their content and look for a match.”

Why you should say it: Out-of-memory errors are some of the most common and hard-to-fix problems that PHP developers encounter in the course of their workday. A more experienced developer understands the limitations of the language and knows how to work around its shortcomings.

“Describe an HTTP request from start to finish.”

Potential answer: “The browser submits an HTTP request message to the server using plain ASCII text. The first line of the request contains some basic information, but the header contains the major operating parameters of an HTTP transaction. Specially, the header defines things such as from, accept, user-agent, accept-encoding, accept-language, if-match, referrer, authorization, modifications and dates as well as pragma. An HTTP request has over 20 steps, would you like me to go through all of them?” (If you need help, here are some additional ways to make HTTP requests in PHP.)

Why you should say it: Demonstrating a fundamental knowledge of the foundational building blocks of Web requests is important. Especially in things like REST APIs where the HTTP action (the “verb”) is a key component of the request.

“Describe the most common PHP security issues.”

Potential answer: “I’m familiar with dozens of issues including source code revelation, remote file inclusion, session hijacking, cross site request forgery (CSRF) and directory traversal. New issues come up all the time.”

Why you should say it: An experienced developer takes security seriously, stays-up-to-date on the latest issues, and is committed to writing secure code. He or she demonstrates an understanding of the risks and how to fix/prevent the issues or where to go for help. Security is yet another piece of the puzzle and has to be balanced with other things—like speed, usability, etc.—when the work is decided on.

“What is separation of concerns and how does it relate to MVC applications?”

Potential answer: “Separation of concerns is a way to build layered applications and a key component of object-oriented architecture. It breaks an app down into distinct features based on functionality, making it easy for multiple development teams to work simultaneously or change existing code. The MVC design pattern encourages separation of concerns by assigning objects in an application one of three roles: model, view or controller. Some of the benefits of MVC include clarity of design, ease of growth and the ability to create multiple interfaces using the same data.”

Why you should say it: Well-structured applications provide separation of concerns because it creates scalability, multiple views and powerful user interfaces. Proficient developers have a base understanding of object-oriented architecture and know how to use the concepts to create robust, flexible applications that support diverse users today and in the future.

“Tell us about yourself and your interest in PHP development.”

Potential answer: Briefly discuss your educational background and highlight relevant projects. Explain what initially drew you to PHP and how your interest has evolved. Mention specific aspects you enjoy, like building user interfaces or backend logic.

Why you should say it: This is your opportunity to showcase your career arc and how you’ve become a master of all things PHP-related.

“What are your greatest strengths and weaknesses as a PHP developer?”

Potential answer: Acknowledge your strengths (for example: problem-solving, analytical skills, or experience with specific frameworks like Laravel). Then, pivot to a weakness, emphasizing how you’re actively trying to improve yourself in that arena, whether it’s knowledge of a new library or something else. Interviewers respond strongly when you exhibit a willingness to learn and grow. 

Why you should say it: Everyone has a weakness; if you don’t come to your interview prepared with one, your interviewer may look at you strangely. The key here is to emphasize that you learn and adapt, making up for your weaknesses and buttressing your strengths as you learn more.

“Describe your experience with object-oriented programming (OOP) in PHP.”

Potential answer: Explain the basic OOP principles: classes, objects, inheritance, polymorphism, and encapsulation. Discuss how you've leveraged these concepts in previous projects. Here’s a breakdown if you need it.

Why you should say it: OOP is a core concept in PHP development.

“How would you debug a critical error in a live production environment?”

Potential answer: Outline a step-by-step process: identifying the error message, analyzing logs, using debugging tools (e.g., Xdebug), and replicating the issue in a development environment. Emphasize clear communication with the team and caution while making production code changes.

Why you should say it: Most interviewers will want you to demonstrate your ability to fix things quickly under pressure. You can improve your answer even more by describing times in which you swooped in to repair an issue at a critical moment.

“Explain the concept of dependency injection in PHP.”

Potential answer: Define dependency injection as a technique to provide dependencies (objects) to a function or class rather than creating them within the code itself. Explain how it promotes loose coupling and improves testability. (Here’s a more detailed run-through if you’re interested.)

Why you should say it: Dependency injection is a best practice for maintainable code, so the chances it will pop up in an interview are high.

“Walk us through the process of connecting to a database using PHP and PDO.”

Potential answer: Explain the steps involved in establishing a PDO connection: specifying the database type, host, username, and password. Demonstrate how to construct queries using prepared statements to prevent SQL injection.

Why you should say it: This assesses your database interaction skills.

“How would you handle user authentication and authorization in a PHP application?”

Potential answer: Discuss secure password hashing and storage techniques. Explain using sessions or tokens for user authentication and implementing role-based access control (RBAC) for authorization, ensuring users only access authorized functionalities.

Why you should say it: Security is a critical aspect of any developer job, and companies will want to see how you weave your security knowledge into your coding and workflows.