If you’ve ever wondered how to interact with websites and APIs directly from your terminal, curl is the tool you need to know. This guide will walk you through everything from what curl is to how to use it effectively.
What is curl?
curl (short for “Client URL”) is a powerful command-line tool that lets you transfer data to or from a server using URLs. Think of it as your terminal’s web browser—but instead of clicking buttons, you type commands.
Why use curl?
- Test APIs without needing a graphical interface
- Download files quickly from the command line
- Automate tasks in scripts
- Debug web requests to see exactly what’s happening
- Work with multiple protocols (HTTP, HTTPS, FTP, and more)
Getting Started: Basic curl Commands
1. View Website Content
The simplest curl command fetches and displays webpage content:
curl https://example.com
This retrieves the HTML of the website and displays it in your terminal.
2. Download Files
To save a file from the internet:
curl -O https://example.com/file.txt
The -O flag tells curl to save the file with its original name.
Want to give it a different name?
curl -o myfile.txt https://example.com/file.txt
3. Send Data to a Server
When working with APIs, you often need to send data:
curl -X POST -d "name=Sonny" https://api.example.com/submit
-X POSTspecifies the HTTP method (POST, GET, PUT, DELETE, etc.)-dsends data in the request body
4. Work with Authentication
Many APIs require credentials:
curl -u username:password https://example.com
The -u flag handles basic authentication for you.
Understanding curl -s (Silent Mode)
One of the most useful flags is -s, which enables silent mode.
What happens normally?
When you run curl without any flags, you see a progress meter:
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1256 100 1256 0 0 4891 0 --:--:-- --:--:-- --:--:-- 4891
What does -s do?
curl -s https://example.com
With -s (or --silent), curl will:
✅ Hide the progress meter
✅ Suppress error messages
✅ Show only the actual output
This is perfect when you want clean output, especially in scripts.
Pro tip: Silent but show errors
Sometimes you want silent mode but still need to see if something went wrong:
curl -sS https://example.com
The -S flag (capital S) shows errors even in silent mode.
Common curl Flags You Should Know
| Flag | What it does | Example |
|---|---|---|
-O | Save file with original name | curl -O https://site.com/file.zip |
-o | Save file with custom name | curl -o custom.zip https://site.com/file.zip |
-s | Silent mode (no progress) | curl -s https://api.com/data |
-S | Show errors in silent mode | curl -sS https://api.com/data |
-X | Specify HTTP method | curl -X POST https://api.com |
-d | Send data | curl -d "key=value" https://api.com |
-H | Add custom headers | curl -H "Content-Type: application/json" |
-u | Authentication | curl -u user:pass https://site.com |
-L | Follow redirects | curl -L https://short.link |
-I | Get headers only | curl -I https://example.com |
Practical Examples
Example 1: Check if a website is up
curl -sS -o /dev/null -w "%{http_code}" https://example.com
This returns just the HTTP status code (like 200 for success).
Example 2: Download with progress bar
curl -# -O https://example.com/largefile.zip
The -# shows a simple progress bar instead of the detailed meter.
Example 3: Send JSON data to an API
curl -X POST https://api.example.com/users \
-H "Content-Type: application/json" \
-d '{"name":"John","email":"john@example.com"}'
Example 4: Save API response to file
curl -s https://api.github.com/users/octocat > user.json
Example 5: Follow redirects
Some URLs redirect to other pages. Use -L to follow them:
curl -L https://bit.ly/shortened-url
Supported Protocols
curl isn’t just for websites—it supports many protocols:
- HTTP/HTTPS – Web requests
- FTP/FTPS – File transfers
- SMTP – Sending emails
- IMAP/POP3 – Reading emails
- SCP/SFTP – Secure file transfers
- And many more!
Tips for Beginners
- Start simple: Begin with basic
curl https://example.comcommands before adding flags - Use -v for debugging: The
-v(verbose) flag shows you everything happening behind the scenes - Combine flags: You can use multiple flags together like
curl -sS -L -o file.txt - Check the manual: Run
curl --helporman curlfor complete documentation - Practice with public APIs: Try https://api.github.com or https://jsonplaceholder.typicode.com for safe testing
Common Use Cases
For Developers
- Testing REST APIs during development
- Automating file downloads in deployment scripts
- Checking server responses and headers
- Debugging authentication issues
For DevOps/Security
- Health checks for services
- Monitoring endpoint availability
- Testing SSL certificates
- Scanning for security headers
For Daily Tasks
- Downloading files from the terminal
- Checking website status
- Fetching data for scripts
- Quick web scraping
Troubleshooting
Problem: Getting SSL certificate errors
Solution: Use -k to skip certificate validation (only for testing!)
curl -k https://self-signed-cert.example.com
Problem: curl command too long
Solution: Use a config file or break it into multiple lines with \
curl -X POST \
-H "Content-Type: application/json" \
-d '{"data":"value"}' \
https://api.example.com
Problem: Need to see what’s being sent
Solution: Use verbose mode with -v
curl -v https://example.com
Summary
curl is an essential tool for anyone working with web technologies. Whether you’re:
- A developer testing APIs
- A sysadmin monitoring services
- A beginner learning web protocols
- Someone who just wants to download files efficiently
…curl has you covered.
Key takeaway: curl -s gives you clean output by hiding progress meters—perfect for scripts and when you just want the data.
Start experimenting with these commands, and you’ll quickly see why curl is installed on virtually every system by default!
Ready to practice? Try running curl -s https://api.github.com/zen for a random piece of GitHub wisdom!
Leave a Reply