$_SERVER information in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of accessing $_SERVER['REQUEST_METHOD']?

Consider a PHP script accessed via a POST request. What will echo $_SERVER['REQUEST_METHOD']; output?

PHP

<?php
// Assume this script is accessed via POST method
echo $_SERVER['REQUEST_METHOD'];
?>

A POST

B GET

C PUT

D DELETE

💡 Hint

Think about how the HTTP method used to access the page is stored in $_SERVER.

The $_SERVER['REQUEST_METHOD'] contains the HTTP method used to access the page. If the request is POST, it will output "POST".

❓ Predict Output

intermediate

What does $_SERVER['HTTP_USER_AGENT'] contain?

If you run echo $_SERVER['HTTP_USER_AGENT']; in a PHP script, what kind of information will it output?

PHP

<?php
echo $_SERVER['HTTP_USER_AGENT'];
?>

A The browser and operating system details of the client

B The server software version

C The requested URL path

D The IP address of the client

💡 Hint

User agent strings describe the client software making the request.

$_SERVER['HTTP_USER_AGENT'] contains the user agent string sent by the browser. This string usually includes browser name, version, and operating system details.

🧠 Conceptual

advanced

Which $_SERVER key gives the absolute path of the currently executing script?

You want to get the full filesystem path to the PHP script currently running. Which $_SERVER key should you use?

A 'REQUEST_URI'

B 'PHP_SELF'

C 'SCRIPT_FILENAME'

D 'DOCUMENT_ROOT'

💡 Hint

Think about the difference between URL paths and filesystem paths.

$_SERVER['SCRIPT_FILENAME'] contains the absolute filesystem path to the currently executing script.

PHP_SELF is the path relative to the web root, REQUEST_URI is the URI requested, and DOCUMENT_ROOT is the root directory of the web server.

❓ Predict Output

advanced

What error occurs when accessing an undefined $_SERVER key?

What happens if you try to echo $_SERVER['NON_EXISTENT_KEY'] in PHP?

PHP

<?php
echo $_SERVER['NON_EXISTENT_KEY'];
?>

A Throws a fatal error and stops script execution

B Outputs an empty string with a PHP Notice about undefined index

C Outputs the string 'NON_EXISTENT_KEY'

D Outputs NULL silently without any error

💡 Hint

PHP warns about undefined array keys but does not stop execution by default.

Accessing an undefined key in $_SERVER triggers a PHP Notice about an undefined index but outputs an empty string. The script continues running.

🧠 Conceptual

expert

How to securely get the client's IP address using $_SERVER?

Which $_SERVER key is the most reliable and secure to get the client's real IP address in PHP?

A 'SERVER_ADDR'

B 'HTTP_X_FORWARDED_FOR'

C 'HTTP_CLIENT_IP'

D 'REMOTE_ADDR'

💡 Hint

Some keys can be spoofed by the client or proxies.

$_SERVER['REMOTE_ADDR'] contains the IP address from which the request was sent to the web server. It is the most reliable source for the client's IP.

Other keys like HTTP_X_FORWARDED_FOR or HTTP_CLIENT_IP can be spoofed by the client or proxies and should not be trusted without validation.