cURL has become an essential tool for developers and sysadmins alike. This versatile command-line tool for transferring data using various protocols allows you to interact with APIs web services servers, and more. As cURL continues to grow in popularity, expect more interviewers to test your cURL skills with targeted questions.
To help you ace your next technical interview, here are the top 25 most common cURL interview questions with example answers
1. What is cURL and what is it commonly used for?
cURL (Client URL) is a command-line tool that allows you to transfer data to and from a server using one of its many supported protocols cURL is most commonly used for
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Interacting with REST APIs – cURL lets you easily send GET, POST, PUT, DELETE requests to API endpoints.
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Downloading or uploading files via FTP, SFTP, SCP
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Testing web applications by sending requests and examining responses
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Automating data transfers for backup, web scraping, etc.
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Debugging connection issues by providing detailed request/response information
2. How does cURL handle HTTP requests and responses?
cURL handles HTTP requests by establishing a connection with the target server, constructing the HTTP request with headers, method, and body, sending the request, and then waiting for a response.
The server processes the request and sends back an HTTP response containing status codes, response headers, and body content.
cURL receives the response, closes the connection, and displays the output. Features like cookies and authentication can be handled using cURL options.
3. Give an example of using cURL to send a POST request with JSON data.
curl -X POST -H "Content-Type: application/json" -d '{"key1":"value1"}' http://example.com/apiThis sends a POST request to the API endpoint with a JSON payload.
-X POST sets method to POST, -H adds a header, -d provides the JSON data for request body.
4. How is cURL different from wget?
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cURL supports many more protocols – HTTP, HTTPS, FTP, SFTP, SMTP, POP3, Telnet, etc. wget only supports HTTP, HTTPS and FTP.
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cURL can be built into applications using libcurl. wget runs standalone.
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cURL displays output to stdout by default. wget shows a progress bar.
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cURL supports downloading multiple files in parallel. wget specializes in recursive mirroring of sites.
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cURL is better for APIs, web apps testing, automation. wget is great for mirroring websites.
5. How can you use cURL to download multiple files simultaneously?
To download multiple files concurrently with cURL:
# Bash curl -O url1 & curl -O url2 & curl -O url3# Pythonimport threading import osdef download(url): os.system(f"curl -O {url}")urls = ["url1", "url2", "url3"]threads = [threading.Thread(target=download, args=(url,)) for url in urls]for thread in threads: thread.start()We run each cURL command in background thread to enable parallel downloads.
6. How would you use cURL to interact with a REST API?
To interact with a REST API using cURL:
- Use HTTP GET request:
curl https://api.example.com/endpoint - POST data:
curl -X POST -d '{"key":"value"}' https://api.example.com/endpoint - Set request headers like Authentication using -H flag
- Handle response codes and errors appropriately
- Use -i to view response headers, -o to save response to file
Refer to API documentation for required headers, authentication, request/response format.
7. How can you maintain session cookies when using cURL?
Use -c cookie-file option to save cookies to a file on first request:
curl -c cookies.txt https://example.com Then use -b cookie-file to send cookies in subsequent requests:
curl -b cookies.txt https://example.com/user-dashboardThis maintains session by sending cookies stored in cookies.txt with every request.
8. What is the basic syntax for sending a GET request with cURL?
curl https://example.comThis sends a GET request to the specified URL.
To save response to file:
curl -o file.txt https://example.com 9. How can you debug problems and handle errors in cURL?
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Use CURLOPT_VERBOSE option to get detailed debug output
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curl_getinfo() returns information on the request/response
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curl_errno() and curl_error() provide error code and message
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Temporarily disable SSL verification with -k option
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Capture core dump on crash for debugging with –dump-header option
Carefully analyze error messages and debug output to fix issues.
10. Give an example of using cURL with a proxy server.
curl -x http://proxy.example.com:8080 https://example.comThis sends the request to https://example.com through proxy server proxy.example.com on port 8080 (replace with actual proxy host/port).
If proxy needs authentication:
curl -x user:password@proxy.example.com:8080 https://example.com11. How can you upload a file to a server with cURL?
To upload a file use the -T option followed by file path:
curl -T localfile.txt -u user:pass ftp://example.com/upload/This uploads localfile.txt to the upload folder on the FTP server using the provided username and password.
12. How does cURL handle SSL connections and certificates?
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Use –cacert to specify CA bundle for verifying peer certificate
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–capath to specify directory of CA certs
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–cert to provide client side certificate
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–key for private key if required
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–insecure to skip verification but not recommended
Handle SSL connections carefully to avoid man-in-the-middle attacks.
13. How can you authenticate using username and password with cURL?
Use the -u option followed by username:password to enable server authentication:
curl -u myusername:password https://example.comThis will pass the credentials using HTTP Basic authentication.
For HTTP Digest authentication use –digest option.
14. What does the -I option do in cURL?
The -I or –head option fetches only the HTTP headers for a given request. It sends a HEAD request for fetching metadata without downloading the actual response body.
curl -I https://example.com 15. How can cURL be used to monitor website performance?
Use -w option to print timing details:
curl -o /dev/null -s -w "Connect: %{time_connect} TTFB: %{time_starttransfer} Total time: %{time_total}n" https://example.comThis fetches https://example.com, discards output, prints timing metrics for connection, TTFB, and total time taken.
16. When would you use the -k (–insecure) option in cURL?
The -k or –insecure option is used to bypass SSL certificate validation and proceed even if site uses untrusted/self-signed certs. This exposes you to man-in-the-middle attacks so only use it for testing on trusted networks.
17. Give an example of using cURL to interact with a REST API.
To send a GET request to a REST API endpoint:
curl https://api.example.com/resourcesTo POST data to create a resource:
curl -X POST -H "Content-Type: application/json" -d '{"name":"xyz"}' https://api.example.com/resourcesYou can also use PUT, DELETE and handle headers, params and auth as needed.
18. How can you access a URL protected by HTTP basic authentication using cURL?
curl -u username:password https://example.comThe -u option provides the username and password to enable basic authentication. Omitting password prompts for it interactively.
19. How do you follow redirects with cURL?
Use the -L option to automatically follow redirects:
curl -L https://example.comThis will follow redirects until the final URL is reached. To avoid infinite loops specify max redirects:
curl --max-redirs 5 https://example.com20. How can cURL be use
Can Curl be used for programming mobile phones or PDA’s? edit
No, not yet. In the event that the Asian market brings in enough money, Curl could be brought to these devices.
Why is your baby son a worshipped deity? edit
I dont understand the question.
Linux Essentials: Curl Fundamentals
FAQ
What is curl and why it is used?
How to explain rest API in interview?
What happens when you type curl?
What is curl format?
What is a curl request?
cURL is a command-line tool used for transferring data with URLs. When making POST requests with cURL, the general structure can be described as: Here are the flags and options relevant to POST requests: -X, –request: Specifies the HTTP method to be used. For a POST request, this would be -X POST.
Are natural curls a good fit for a job interview?
While it seems that the times are changing and people are becoming more accepting of natural curls and textures, there is still some work to be done. When it comes to interviews, it can be extra nerve wracking if you’re afraid your prospective employer won’t accept your natural style.
How long did a curl interview last?
The interview went on for 2 weeks. I had a great experience attending the interview with curl. There was a total of 4 rounds of interviews, 2 were technical rounds followed by a discussion with the manager, and an HR round for a salary discussion.
What is curl & how do I use it?
Curl is a command-line tool that allows us to do HTTP requests from shell. It also covers many other protocols, like FTP, though they go beyond the scope of this tutorial. Its name stands for “Client URL”, and it was developed by Swedish developer Daniel Stenberg.
