In PHP, how can you get information about the client browser such as name and version?

Introduction / Context:
Many PHP applications want to adapt behaviour based on the client browser, such as serving different layouts to mobile devices or handling legacy browsers. To do this, the application needs access to browser related information coming from the HTTP request. Interview questions often ask how to get browser properties in PHP to ensure that candidates understand the role of request headers, the $_SERVER superglobal, and helper functions like get_browser().

Given Data / Assumptions:

• The client browser sends an HTTP request that includes a User Agent header.
• PHP exposes request and server information through the $_SERVER superglobal array.
• PHP provides an optional get_browser() function which can return structured information if configured with a browscap file.
• The task is to obtain browser information in a typical PHP web application.

Concept / Approach:
The fundamental concept is that the web server does not guess browser details; it reads the User Agent string that the browser sends in the HTTP headers. PHP makes this header available via the $_SERVER array as HTTP_USER_AGENT. Developers can read this string directly or pass it to libraries that parse it. Additionally, PHP offers get_browser(), which attempts to map the User Agent string to a structured set of properties such as browser name, version, and capabilities, based on the browscap configuration. However, get_browser() requires additional setup and is not always enabled on shared hosts.

Step-by-Step Solution:
Step 1: Access the raw User Agent string by reading $_SERVER["HTTP_USER_AGENT"] in your PHP script. This gives you the browser identification that the client sent. Step 2: If you only need simple checks, you can search within this string, for example checking whether it contains substrings for known browsers or device types. Step 3: For more detailed information, configure the browscap directive in php.ini to point to a browscap file that describes many known User Agent strings. Step 4: Once browscap is configured, you can call get_browser(null, true) to obtain an associative array of browser properties, including browser name, version, and platform. Step 5: Use this data to make decisions in your application, but always fall back gracefully because User Agent data can be missing or spoofed. Step 6: This workflow shows that reading HTTP_USER_AGENT or using get_browser() are the standard ways to access browser properties in PHP.

Verification / Alternative check:
You can verify this by writing a small PHP script that echoes $_SERVER["HTTP_USER_AGENT"] and running it from different browsers and devices. The output will change according to the browser, confirming that the value comes from the client. If you configure browscap and call get_browser(), you will see a structured array describing the browser. No database queries or automatic session variables are involved, which supports the explanation above.

Why Other Options Are Wrong:
Option b is wrong because phpinfo() is meant for diagnostics and outputs a full HTML page; parsing it on every request would be inefficient and unreliable. Option c is incorrect because there is no built in BROWSER session variable; sessions only store what the developer puts into them. Option d is wrong because browser data is not stored in a server database by default; it is sent by the client on each request via HTTP headers.

Common Pitfalls:
A common pitfall is relying too heavily on User Agent detection for critical functionality, even though User Agent strings can be spoofed or changed. Another is assuming that get_browser() will work automatically without configuring browscap, which leads to unexpected empty or incomplete results. Best practice is to use feature detection on the client side where possible, use server side browser checks only when necessary, and handle unknown or misleading User Agent values safely.

Final Answer:
You can get browser properties in PHP by reading the HTTP_USER_AGENT value from the $_SERVER superglobal or by using the get_browser() function with a configured browscap file to obtain structured information about the client browser.