curl for HTTP requests in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send a simple GET request to example.com using curl.

Linux CLI

curl [1]

Drag options to blanks, or click blank then click option'

A-d 'data' http://example.com

B-X POST http://example.com

Chttp://example.com

D-I http://example.com

Attempts:

3 left

💡 Hint

Common Mistakes

Using -X POST when you want a GET request.

Adding data (-d) when not needed.

Using -I which only fetches headers.

The simplest way to send a GET request with curl is to provide the URL directly without extra options.

2fill in blank

medium

Complete the code to send a POST request with curl to http://example.com.

Linux CLI

curl [1] http://example.com

Drag options to blanks, or click blank then click option'

A-X GET

B-X POST

C-L

D-I

Attempts:

3 left

💡 Hint

Common Mistakes

Using -X GET instead of POST.

Using -I which only fetches headers.

Using -L which follows redirects but does not change method.

Use -X POST to specify the POST method explicitly with curl.

3fill in blank

hard

Fix the error in the curl command to send JSON data with POST to http://example.com.

Linux CLI

curl -X POST -H 'Content-Type: application/json' -d [1] http://example.com

Drag options to blanks, or click blank then click option'

A"name=John"

B{"name":"John"}

C'name=John'

D'{"name":"John"}'

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting JSON properly causing shell errors.

Using URL-encoded format instead of JSON.

Missing quotes causing syntax errors.

JSON data must be a properly quoted string. Single quotes around the JSON string prevent shell issues.

4fill in blank

hard

Fill both blanks to save the output of a curl GET request to a file named response.txt.

Linux CLI

curl [1] [2]

Drag options to blanks, or click blank then click option'

A-o response.txt

Bhttp://example.com

C-O

D-I

Attempts:

3 left

💡 Hint

Common Mistakes

Using -I which only fetches headers.

Using -O which saves with original filename, not custom.

Putting options in wrong order.

Use -o with the filename before the URL to save output to that file.

5fill in blank

hard

Fill all three blanks to send a POST request with JSON data and include a custom header.

Linux CLI

curl [1] -H [2] -d [3] http://example.com

Drag options to blanks, or click blank then click option'

A-X POST

B'Authorization: Bearer token123'

C'{"id":5}'

D-I

Attempts:

3 left

💡 Hint

Common Mistakes

Using -I which only fetches headers.

Not quoting header or data properly.

Missing -X POST option.

Use -X POST to set method, -H for custom header, and -d for JSON data.

Practice

1. What does the curl command primarily do in Linux?

easy

A. Monitor system processes

B. Send HTTP requests to websites

C. Manage file permissions

D. Compile source code

Solution

1. Step 1: Understand the purpose of curl

   The curl command is designed to send HTTP requests and interact with web servers.

2. Step 2: Compare with other options

   Compiling code, managing permissions, and monitoring processes are unrelated to curl's function.

3. Final Answer:

   Send HTTP requests to websites -> Option B

4. Quick Check:

   curl = HTTP requests [OK]

Hint: curl is for web requests, not system tasks [OK]

Common Mistakes:

• Confusing curl with system commands like chmod or ps
• Thinking curl compiles code
• Assuming curl manages files locally

2. Which of the following is the correct syntax to fetch the content of http://example.com using curl?

easy

A. curl http://example.com

B. curl --head http://example.com

C. curl -x http://example.com

D. curl -d http://example.com

Solution

1. Step 1: Identify basic curl usage

   To fetch a webpage, simply use curl URL. No extra flags are needed for a simple GET request.

2. Step 2: Analyze other options

   -x is for proxy, --head fetches headers only, -d sends data (POST), so they are incorrect for simple fetch.

3. Final Answer:

   curl http://example.com -> Option A

4. Quick Check:

   Basic fetch = curl URL [OK]

Hint: Use curl followed by URL to fetch page [OK]

Common Mistakes:

• Using -x which is for proxy
• Using -d which sends data instead of fetching
• Using --head which fetches headers only

3. What will be the output of this command?

curl -I https://example.com

medium

A. An error because -I is invalid

B. The full HTML content of the page

C. Only the HTTP headers of the response

D. The page content saved to a file

Solution

1. Step 1: Understand the -I option in curl

   The -I flag tells curl to fetch only the HTTP headers, not the full content.

2. Step 2: Check other options

   The full HTML content of the page is full content, which -I does not do. An error because -I is invalid is wrong because -I is valid. The page content saved to a file requires -o flag, not present here.

3. Final Answer:

   Only the HTTP headers of the response -> Option C

4. Quick Check:

   -I = headers only [OK]

Hint: Remember -I fetches headers only [OK]

Common Mistakes:

• Thinking -I fetches full page
• Confusing -I with -o for output file
• Assuming -I is invalid flag

4. You want to send JSON data {"name":"John"} to http://api.example.com/users using curl. Which command has an error?

medium

A. curl -d '{name:John}' -X POST -H "Content-Type: application/json" http://api.example.com/users

B. curl -X POST -H "Content-Type: application/json" -d '{"name":"John"}' http://api.example.com/users

C. curl -d '{"name":"John"}' http://api.example.com/users -H "Content-Type: application/json" -X POST

D. curl -X POST -d '{"name":"John"}' -H "Content-Type: application/json" http://api.example.com/users

Solution

1. Step 1: Check JSON data format

   curl -d '{name:John}' -X POST -H "Content-Type: application/json" http://api.example.com/users uses '{name:John}' which misses double quotes around keys and values, making it invalid JSON. Options A, C, D use correct JSON '{"name":"John"}'.

2. Step 2: Confirm curl flags order

   Order of flags does not matter in curl, so A, C, D are valid. Only data format in B is wrong.

3. Final Answer:

   curl -d '{name:John}' -X POST -H "Content-Type: application/json" http://api.example.com/users -> Option A

4. Quick Check:

   JSON must have quotes [OK]

Hint: JSON keys and values need quotes [OK]

Common Mistakes:

• Omitting quotes in JSON data
• Thinking flag order matters in curl
• Using wrong content-type header

5. You want to download a file from http://example.com/file.zip and save it as myfile.zip. Which curl command does this correctly?

hard

A. curl --save myfile.zip http://example.com/file.zip

B. curl -O http://example.com/file.zip > myfile.zip

C. curl -O myfile.zip http://example.com/file.zip

D. curl -o myfile.zip http://example.com/file.zip

Solution

1. Step 1: Understand curl file saving options

   -o filename saves the download to the specified filename. -O saves with original name from URL.

2. Step 2: Analyze each option

   B: curl -O http://example.com/file.zip > myfile.zip saves to 'file.zip' via -O and redirects empty stdout to myfile.zip. C: curl -O myfile.zip http://example.com/file.zip uses -O incorrectly, treating myfile.zip as URL. D: uses invalid flag --save.

3. Final Answer:

   curl -o myfile.zip http://example.com/file.zip -> Option D

4. Quick Check:

   -o sets output filename [OK]

Hint: Use -o to name downloaded file [OK]

Common Mistakes:

• Using > redirection for binary files
• Confusing -O and -o flags
• Using non-existent flags like --save