Exploring cURL: The Command-Line Power Tool for Web Developers and Cyber Experts

By Shanu Mathew |Managing Editor| Brutnow Media 

cURL—short for Client URL—is one of the most powerful and versatile command-line tools available for transferring data using URLs. It supports a wide array of protocols including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, LDAP, and more. Whether you’re a developer, system administrator, cybersecurity analyst, or OSINT investigator, cURL is an essential part of your toolkit.

🌍 What Is cURL?

At its core, cURL is a utility that allows you to send and receive data from servers directly from the terminal or command line. It works on Linux, macOS, Windows, and nearly every modern operating system. It is especially useful for interacting with REST APIs, downloading or uploading files, and automating repetitive web-based tasks.

💡 Why Use cURL?

• ✅ Test APIs and endpoints directly
• ✅ Debug network requests
• ✅ Automate login forms, uploads, and data transfers
• ✅ Simulate browser requests
• ✅ Troubleshoot server issues

⚙️ Basic Syntax

curl [OPTIONS] [URL]

Example:

curl https://example.com

This command fetches the HTML content of the homepage.

Most Powerful cURL Commands

1. 📄 Make a GET Request (Default)

curl https://jsonplaceholder.typicode.com/posts/1

This retrieves a JSON response from a test API.

2. ✍️ POST Data to a Server

curl -X POST https://jsonplaceholder.typicode.com/posts \
     -H "Content-Type: application/json" \
     -d '{"title":"Hello","body":"World","userId":1}'

This sends a JSON payload to the server using POST.

3. 🔐 Include Custom Headers (Like Tokens)

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" https://api.example.com/data

Used for authenticated requests, especially with REST APIs.

4. 💾 Download a File

curl -O https://example.com/file.zip

The -O flag tells cURL to save the file with its original filename.

5. 📂 Upload a File

curl -F "file=@example.txt" https://example.com/upload

The -F option simulates file uploads via multipart/form-data.

6. 🌐 Follow Redirects Automatically

curl -L https://bit.ly/example

This ensures that cURL follows 301/302 redirects.

7. 📃 Save Output to a File

curl https://example.com -o homepage.html

This saves the HTML content of a website to a file.

8. 🕵️ View HTTP Headers Only

curl -I https://example.com

Displays only the response headers (uses a HEAD request).

9. 💬 Send URL-Encoded Form Data

curl -X POST -d "username=admin&password=123456" https://example.com/login

Useful for simulating traditional web form submissions.

10. 📊 Verbose Mode for Debugging

curl -v https://example.com

Displays the full request/response communication including SSL handshake, DNS resolution, and headers.

🛠️ Summary of Common cURL Flags

🔐 Security Best Practices

• Don’t store or expose your API tokens in public scripts.
• Use HTTPS for secure communication.
• Sanitize and validate inputs when automating requests.
• Test APIs in safe environments before going live.

🎯 Real-World Use Cases

• Developers: Test API endpoints quickly.
• Security Analysts: Check server headers, SSL certificates, simulate brute-force or fuzzing attacks.
• System Administrators: Automate server interactions, update files, or check connectivity.
• OSINT Investigators: Retrieve metadata, analyze web headers, and extract resources for profiling.

📌 Conclusion

cURL is far more than just a downloader—it’s a robust data transfer engine that can emulate nearly any type of HTTP client behavior. Once you master its core commands, you can easily test APIs, debug applications, automate uploads/downloads, and enhance your command-line workflow.

Whether you’re debugging a failing REST call or scripting a full data pipeline, cURL is the power tool you’ll always want by your side.

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