HTTP requests with curl in scripts in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this curl command?

You run this command in a terminal to get the HTTP status code of a website:

curl -o /dev/null -s -w "%{http_code}" https://example.com

What will this command output?

Bash Scripting

curl -o /dev/null -s -w "%{http_code}" https://example.com

A The full HTML content of https://example.com

B 200

C An error message about missing output file

D Nothing (blank output)

💡 Hint

The flags -o /dev/null and -s hide the content and progress, -w "%{http_code}" prints the status code.

The command fetches the URL but discards the body (-o /dev/null), runs silently (-s), and prints only the HTTP status code (-w "%{http_code}"). For a successful request, it outputs 200.

💻 Command Output

intermediate

What does this curl command output?

This command sends a POST request with JSON data:

curl -X POST -H "Content-Type: application/json" -d '{"name":"Alice"}' https://httpbin.org/post

What kind of output will you get?

Bash Scripting

curl -X POST -H "Content-Type: application/json" -d '{"name":"Alice"}' https://httpbin.org/post

A No output, command runs silently

B The HTML page of httpbin.org homepage

C A JSON response showing the data sent and request details

D An error about unsupported HTTP method

💡 Hint

httpbin.org/post echoes back the POST data in JSON format.

The command sends JSON data to httpbin.org/post, which responds with JSON showing the data received and other request info.

🔧 Debug

advanced

Why does this curl command fail with a certificate error?

You run this command:

curl https://self-signed.badssl.com/

It fails with an SSL certificate error. Which option fixes this error by ignoring certificate validation?

Bash Scripting

curl https://self-signed.badssl.com/

A curl --insecure https://self-signed.badssl.com/

B curl --no-ssl https://self-signed.badssl.com/

C curl --ignore-certs https://self-signed.badssl.com/

D curl --skip-verify https://self-signed.badssl.com/

💡 Hint

The option to ignore SSL certificate errors is --insecure or -k.

The --insecure flag tells curl to skip SSL certificate verification, allowing connection to servers with self-signed or invalid certificates.

🚀 Application

advanced

How to save HTTP response headers to a file using curl?

You want to save only the HTTP response headers from a GET request to https://example.com into a file named headers.txt. Which command does this correctly?

A curl -D headers.txt https://example.com -o /dev/null

B curl -H headers.txt https://example.com

C curl -I https://example.com > headers.txt

D curl --headers https://example.com > headers.txt

💡 Hint

The -D option saves headers to a file; -o /dev/null discards the body.

Using -D headers.txt saves the response headers to the file. The -o /dev/null discards the body so only headers are saved.

🧠 Conceptual

expert

What is the effect of this curl command in a script?

Consider this bash script snippet:

response=$(curl -s -w "%{http_code}" -o response.txt https://example.com)

What will be stored in the variable response after running this command?

Bash Scripting

response=$(curl -s -w "%{http_code}" -o response.txt https://example.com)

A An empty string

B The full HTML content of https://example.com

C The path to the saved file response.txt

D The HTTP status code as a string, e.g., "200"

💡 Hint

The -w option outputs the status code to stdout, -o saves body to file, -s silences progress.

The command saves the response body to response.txt (-o response.txt), suppresses progress (-s), and outputs only the HTTP status code (-w "%{http_code}"). This output is captured in the variable response.

Practice

1. What does the curl command do in a bash script?

easy

A. It creates a new directory on the system.

B. It sends HTTP requests to websites or APIs.

C. It compiles the bash script into an executable.

D. It displays the current date and time.

Solution

1. Step 1: Understand the purpose of curl

   The curl command is designed to transfer data from or to a server using various protocols, mainly HTTP.

2. Step 2: Match curl's function to the options

   Among the options, only sending HTTP requests matches curl's purpose.

3. Final Answer:

   It sends HTTP requests to websites or APIs. -> Option B

4. Quick Check:

   curl = HTTP requests [OK]

Hint: Remember curl talks to websites using HTTP [OK]

Common Mistakes:

• Confusing curl with system commands like mkdir or date
• Thinking curl compiles scripts
• Assuming curl only downloads files

2. Which of the following is the correct syntax to send a GET request with curl in a bash script?

easy

A. curl -send https://example.com

B. curl --post https://example.com

C. curl -X GET https://example.com

D. curl get https://example.com

Solution

1. Step 1: Identify the correct curl option for GET

   The -X GET option explicitly tells curl to use the GET method, which is the default.

2. Step 2: Check other options for correctness

   Options B, C, and D use invalid or incorrect flags for curl.

3. Final Answer:

   curl -X GET https://example.com -> Option C

4. Quick Check:

   GET request syntax = curl -X GET [OK]

Hint: Use -X GET to specify GET method explicitly [OK]

Common Mistakes:

• Using --post instead of -X POST for POST requests
• Typing invalid flags like -send or get
• Omitting the URL

3. What will the following script output?

response=$(curl -s -o /dev/null -w "%{http_code}" https://httpbin.org/status/200)
echo $response

medium

A. 200

B. OK

C. 404

D. curl: command not found

Solution

1. Step 1: Understand curl options used

   The -s option silences progress, -o /dev/null discards output, and -w "%{http_code}" prints the HTTP status code.

2. Step 2: Analyze the URL and expected status

   The URL https://httpbin.org/status/200 returns HTTP status 200, so the variable response will hold "200".

3. Final Answer:

   200 -> Option A

4. Quick Check:

   HTTP status code = 200 [OK]

Hint: Use -w "%{http_code}" to get HTTP status code [OK]

Common Mistakes:

• Expecting full page content instead of status code
• Missing quotes around %{http_code}
• Not using -s to silence output

4. Identify the error in this script snippet:

curl -X POST -d 'name=John' https://example.com/api
if [ $? -eq 0 ]; then
  echo "Success"
else
  echo "Failed"
fi

medium

A. No error; script works correctly

B. Missing quotes around URL

C. Single quotes prevent variable expansion in -d

D. Using -X POST with -d is invalid

Solution

1. Step 1: Check curl command syntax

   The command uses -X POST with -d 'name=John' correctly to send POST data.

2. Step 2: Verify script logic for success check

   The script checks the exit status $? properly and echoes success or failure accordingly.

3. Final Answer:

   No error; script works correctly -> Option A

4. Quick Check:

   Script syntax and logic = correct [OK]

Hint: Check exit status $? after curl for success [OK]

Common Mistakes:

• Thinking single quotes block variable expansion here (no variables used)
• Assuming -X POST and -d can't be combined
• Forgetting to check curl exit status

5. You want to write a bash script that sends a JSON POST request with curl to https://api.example.com/data and saves the response to response.json. Which script snippet correctly does this?

hard

A. curl -X POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data >> response.json

B. curl -POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data > response.json

C. curl -X POST -H Content-Type application/json -d '{"key":"value"}' https://api.example.com/data > response.json

D. curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json

Solution

1. Step 1: Check HTTP method and headers

   curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json correctly uses -X POST and sets the header -H 'Content-Type: application/json' with quotes.

2. Step 2: Validate JSON data and output redirection

   curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json uses valid JSON with escaped quotes and redirects output with > to overwrite response.json.

3. Step 3: Identify errors in other options

   curl -POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data > response.json uses invalid -POST flag and unquoted JSON keys. curl -X POST -H Content-Type application/json -d '{"key":"value"}' https://api.example.com/data > response.json misses quotes around header value. curl -X POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data >> response.json appends with >> and has invalid JSON keys.

4. Final Answer:

   curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json -> Option D

5. Quick Check:

   Correct POST JSON syntax and output redirection = curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json [OK]

Hint: Use -H for headers, -d with valid JSON, > to save output [OK]

Common Mistakes:

• Forgetting quotes around JSON keys and values
• Using invalid curl flags like -POST
• Appending instead of overwriting output file