$_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.

Practice

1. What type of data does the PHP $_SERVER superglobal array hold?

easy

A. User input from forms

B. Information about headers, paths, and script locations

C. Database connection details

D. Session variables

Solution

1. Step 1: Understand what $_SERVER contains

   $_SERVER holds server and execution environment information like headers and script paths.

2. Step 2: Compare with other options

   User input is in $_POST or $_GET, database details are not stored here, and session variables are in $_SESSION.

3. Final Answer:

   Information about headers, paths, and script locations -> Option B

4. Quick Check:

   $_SERVER = server info [OK]

Hint: Remember: $_SERVER = server and request info [OK]

Common Mistakes:

• Confusing $_SERVER with $_POST or $_GET
• Thinking $_SERVER holds user session data
• Assuming $_SERVER contains database info

2. Which of the following is the correct way to get the current script's filename using $_SERVER?

easy

A. $_SERVER['SCRIPT_NAME']

B. $_SERVER['USER_AGENT']

C. $_SERVER['REMOTE_ADDR']

D. $_SERVER['HTTP_HOST']

Solution

1. Step 1: Identify the key for current script filename

   $_SERVER['SCRIPT_NAME'] returns the path of the current script.

2. Step 2: Understand other keys

   USER_AGENT is client browser info, REMOTE_ADDR is client IP, and HTTP_HOST is the host name.

3. Final Answer:

   $_SERVER['SCRIPT_NAME'] -> Option A

4. Quick Check:

   Script filename = $_SERVER['SCRIPT_NAME'] [OK]

Hint: SCRIPT_NAME gives current script path [OK]

Common Mistakes:

• Using REMOTE_ADDR for filename
• Confusing HTTP_HOST with script name
• Trying USER_AGENT for script info

3. What will the following PHP code output if the visitor's IP address is 192.168.1.10?

echo $_SERVER['REMOTE_ADDR'];

medium

A. 192.168.1.10

B. The server's IP address

C. The visitor's browser name

D. An empty string

Solution

1. Step 1: Understand what REMOTE_ADDR holds

   $_SERVER['REMOTE_ADDR'] contains the IP address of the client visiting the page.

2. Step 2: Match with given IP

   The visitor's IP is 192.168.1.10, so that is what will be printed.

3. Final Answer:

   192.168.1.10 -> Option A

4. Quick Check:

   REMOTE_ADDR = visitor IP [OK]

Hint: REMOTE_ADDR shows visitor IP address [OK]

Common Mistakes:

• Thinking REMOTE_ADDR is server IP
• Confusing REMOTE_ADDR with HTTP_USER_AGENT
• Expecting browser name instead of IP

4. Identify the error in this PHP code snippet that tries to print the visitor's browser info:

echo $_SERVER[HTTP_USER_AGENT];

medium

A. $_SERVER cannot be echoed directly

B. Using wrong key name

C. Missing quotes around the array key

D. HTTP_USER_AGENT is not available in $_SERVER

Solution

1. Step 1: Check array key syntax

   Array keys must be strings in quotes. Here, HTTP_USER_AGENT is missing quotes.

2. Step 2: Confirm key existence

   HTTP_USER_AGENT is a valid key in $_SERVER, so the key name is correct.

3. Final Answer:

   Missing quotes around the array key -> Option C

4. Quick Check:

   Array keys need quotes [OK]

Hint: Always quote $_SERVER keys like 'HTTP_USER_AGENT' [OK]

Common Mistakes:

• Forgetting quotes around keys
• Assuming key name is wrong
• Trying to echo whole $_SERVER array directly

5. You want to create a PHP script that shows the visitor's IP address and the current script's filename. Which code snippet correctly does this?

hard

A. echo 'IP: ' . $_SERVER['REMOTE_HOST'] . ', Script: ' . $_SERVER['SCRIPT_FILENAME'];

B. echo 'IP: ' . $_SERVER['SCRIPT_NAME'] . ', Script: ' . $_SERVER['REMOTE_ADDR'];

C. echo 'IP: ' . $_SERVER['HTTP_HOST'] . ', Script: ' . $_SERVER['REMOTE_ADDR'];

D. echo 'IP: ' . $_SERVER['REMOTE_ADDR'] . ', Script: ' . $_SERVER['SCRIPT_NAME'];

Solution

1. Step 1: Identify keys for IP and script filename

   REMOTE_ADDR is visitor IP, SCRIPT_NAME is current script path.

2. Step 2: Check code correctness

   echo 'IP: ' . $_SERVER['REMOTE_ADDR'] . ', Script: ' . $_SERVER['SCRIPT_NAME'];

   correctly concatenates IP and script name.

   echo 'IP: ' . $_SERVER['SCRIPT_NAME'] . ', Script: ' . $_SERVER['REMOTE_ADDR'];

   swaps them incorrectly.

   echo 'IP: ' . $_SERVER['HTTP_HOST'] . ', Script: ' . $_SERVER['REMOTE_ADDR'];

   uses HTTP_HOST (server host) instead of IP.

   echo 'IP: ' . $_SERVER['REMOTE_HOST'] . ', Script: ' . $_SERVER['SCRIPT_FILENAME'];

   uses REMOTE_HOST (often empty) and SCRIPT_FILENAME (full path, not filename).

3. Final Answer:

   echo 'IP: ' . $_SERVER['REMOTE_ADDR'] . ', Script: ' . $_SERVER['SCRIPT_NAME']; -> Option D

4. Quick Check:

   IP = REMOTE_ADDR, Script = SCRIPT_NAME [OK]

Hint: Use REMOTE_ADDR for IP and SCRIPT_NAME for script path [OK]

Common Mistakes:

• Mixing up REMOTE_ADDR and SCRIPT_NAME
• Using HTTP_HOST instead of REMOTE_ADDR
• Using REMOTE_HOST which may be empty