PHP Interview Questions

PHP (Hypertext Preprocessor) is a widely-used open-source server-side scripting language designed primarily for web development. It can be embedded within HTML and is especially suited for creating dynamic and interactive websites.

Key Features of PHP:

• Server-Side Language: PHP code runs on the server and generates dynamic content that is sent to the client’s browser.
• Dynamic Content Creation: It can process user input, handle forms, and interact with databases to build data-driven applications.
• Cross-Platform: PHP is compatible with major operating systems like Windows, Linux, and macOS.
• Database Integration: It supports a wide range of databases such as MySQL, PostgreSQL, Oracle, etc., making it ideal for back-end web development.
• Open-Source: PHP is free to use, maintained by a large community of developers worldwide.

Origin: PHP was created by Rasmus Lerdorf in 1994 and has evolved significantly to support modern web development practices.

In PHP, you can redirect a user to another page using the header() function. This function sends a raw HTTP header to the browser instructing it to navigate to a different location. It's commonly used after form submissions, authentication, or when you want to guide users to another part of your application.

Example:

Note: Always call exit() right after header() to stop further script execution. Also, make sure you haven't sent any output (like HTML or echo statements) before using header(), or it will result in a 'headers already sent' error.

In PHP, a session is a way to store data (variables) across multiple pages for an individual user. Unlike cookies, which are stored on the user's browser, session data is stored on the server.

When a session is started using session_start(), PHP generates a unique session ID for each user. This ID is usually stored in a cookie on the client-side and is used to access session data stored on the server.

Example:

This code starts a session, stores a username, and then displays it. The value will be accessible on any other page of the application as long as the session is active.

Both session_unset() and session_destroy() are used to handle session management in PHP, but they differ in how they impact session data and session lifecycle.

Key Differences Between session_unset() and session_destroy():

Full Form of PHP:
PHP stands for Hypertext Preprocessor. It's a recursive acronym where the first 'P' actually stands for 'PHP' itself.

Old Name of PHP:
Originally, PHP stood for Personal Home Page when it was first created by Rasmus Lerdorf in 1994. It was initially designed for managing personal websites before evolving into a powerful server-side scripting language.

PEAR stands for PHP Extension and Application Repository. It is a structured library and distribution system for reusable PHP code components. PEAR provides a command-line interface for installing and managing packages, helping developers save time by reusing code instead of writing it from scratch.

Key Features of PEAR:

• Reusable Code: Offers pre-written PHP packages to avoid redundant code.
• Package Management: Enables easy installation, upgrading, and removal of libraries.
• Standardization: Promotes consistent coding standards and practices across PHP applications.
• Autoloading: Helps in automatically loading PHP classes when needed.
• Command-line Interface (CLI): Provides tools to install and manage packages directly from the terminal.
• Web-based Interface: Allows users to browse and download packages through a web interface.

The following rules must be followed while naming a PHP variable:

• A variable in PHP must start with a dollar sign ($), followed by the variable name. Example: $price = 100;
• Variable names must begin with a letter (a-z, A-Z) or an underscore (_).
• Variable names can contain letters, numbers, and underscores, but cannot contain special characters like +, -, %, &, etc.
• PHP variable names cannot contain spaces.
• PHP variables are case-sensitive, meaning $NAME and $name are considered different variables.

Steps to execute a PHP script from the command line:

1. Open the terminal or command line window.
2. Navigate to the folder or directory where the PHP files are located.
3. Run the PHP file using: php file_name.php
4. To start a server for testing, use: php -S localhost:port -t your_folder/

The crypt() function in PHP can be used for hashing passwords. It supports algorithms such as SHA-1, SHA-256, and MD5. However, these algorithms are no longer considered secure for password hashing due to vulnerabilities to brute-force and rainbow table attacks. Modern applications prefer using password_hash() with PASSWORD_BCRYPT or PASSWORD_ARGON2I.

Yes, JavaScript can interact with PHP, typically through AJAX (Asynchronous JavaScript and XML). JavaScript sends requests to PHP on the server, and PHP processes these requests and returns data (often in JSON or HTML format) to JavaScript for client-side use.

Common use cases include:

• Submitting forms without reloading the page.
• Fetching dynamic data from the server.
• Updating page content based on user actions.

• Notices: Non-critical errors that do not stop script execution. Example: Accessing an undefined variable.
• Warnings: More critical than notices but still allow script execution. Example: Including a non-existent file with include().
• Fatal Errors: Critical errors that stop script execution immediately. Example: Requiring a non-existent file with require().

Constants in PHP are defined using the define() function. Constants are identifiers whose value cannot be changed during the script execution. They are defined without the dollar sign ($).

Example: define("SITE_NAME", "example.com");

• Laravel
• CodeIgniter
• Symfony
• CakePHP
• Yii
• Zend Framework
• Phalcon
• FuelPHP
• PHPixie
• Slim

• WordPress: Open-source CMS, most widely used.
• Joomla: Open-source CMS following the MVC framework.
• Magento: Open-source e-commerce platform.
• Drupal: CMS platform under the GNU General Public License.

• break: Immediately terminates the loop or switch statement and moves control to the statement after it.
• continue: Skips the current iteration of a loop and moves to the next iteration.

The count() function returns the number of elements in an array. It returns 0 for an empty array or an unset variable.

A cookie is a small record that the server installs on the client’s computer to store user-related data in the browser. It is used to identify users and maintain sessions between the client and server.

Cookies store only string values, not objects, and are URL-specific. By default, they are temporary and per site up to 20 cookies can be stored, with a maximum size of 4096 bytes.

In PHP, cookies are created using the setcookie() function:

setcookie(name, value, expire, path, domain, secure, httponly);

Example:

setcookie("instrument_selected", "guitar");

• include(): Includes and evaluates the specified file. If the file is not found, it produces a warning (E_WARNING) but the script continues execution.
• require(): Works like include(), but if the file is not found, it produces a fatal error (E_COMPILE_ERROR) and stops script execution.

The crypt() function is used for password hashing in PHP. It supports various algorithms such as sha1, sha256, and md5. While these are fast, modern best practices recommend using password_hash() with PASSWORD_BCRYPT or PASSWORD_ARGON2I for stronger security.

PHP4 uses Zend Engine 1 and does not support the Object-Oriented Programming (OOP) concept, while PHP5 supports OOP and uses Zend Engine 2.

PHP is partly case-sensitive. Variable names are case-sensitive, but function names are not. User-defined functions are also case-insensitive, but the rest of the language is case-sensitive.

The constant() function is used to retrieve the value of a constant. This value remains unchanged throughout the script’s execution and can be used as a reference for calculations or configuration.

Single-quoted strings are treated as literals and do not parse variables or escape sequences (except for \ and '). Double-quoted strings parse variables and recognize escape sequences, allowing dynamic content within the string.

• Notices: Non-critical errors that occur during script execution and are not shown to the user by default. Example: accessing an undefined variable.
• Warnings: More serious than notices but do not halt script execution. Example: including a non-existent file using include().
• Fatal Errors: Critical errors that immediately terminate the script. Example: requiring a non-existent file using require().

A final class is a class that cannot be extended or inherited by any other class. This means that no other class can subclass it to override or modify its behavior.

Similarly, a final method is a method that cannot be overridden in a subclass. If a method is declared as final, child classes can still inherit it, but cannot provide their own implementation.

Final classes and methods are typically used to preserve intended behavior, enhance security, and prevent accidental changes in critical parts of the code.