cURL (Client URL) is a powerful command-line tool and library used for transferring data with URLs. It supports multiple protocols, including HTTP, HTTPS, FTP, SCP, SFTP, and more. Developers and system administrators commonly use cURL for API interactions, testing endpoints, downloading files, and troubleshooting network issues.

In this guide, we'll cover everything you need to know about cURL, from installation to advanced usage.

Table of Contents

  1. What is cURL?

  2. Installing cURL

  3. Basic cURL Commands

  4. cURL with HTTP Methods (GET, POST, PUT, DELETE)

  5. Sending Headers and Cookies

  6. Handling Authentication with cURL

  7. Uploading and Downloading Files

  8. Working with JSON and APIs

  9. Handling SSL/TLS Certificates

  10. Debugging with cURL

  11. Using cURL in PHP, Python, and Bash

  12. cURL Alternatives

  13. Conclusion

  1. What is cURL?

cURL is a free and open-source command-line utility for transferring data between a client and a server. It was created by Daniel Stenberg in 1996 and is widely used in web development, automation, and testing.

Key Features of cURL:

Supports multiple protocols (HTTP, FTP, SMTP, etc.).

Works on Linux, macOS, and Windows.

Allows sending custom headers, cookies, and authentication.

Can handle file uploads and downloads.

Supports SSL/TLS for secure communication.

  1. Installing cURL

On Linux (Ubuntu/Debian)

sudo apt update sudo apt install curl -y

On CentOS/RHEL

sudo yum install curl -y

On macOS

cURL is pre-installed on macOS. You can check the version using:

curl --version

If you need the latest version, install it using Homebrew:

brew install curl

On Windows

Download the latest cURL package from the official website. Alternatively, install it via Chocolatey:

choco install curl
  1. Basic cURL Commands

Here are some simple cURL commands:

Check cURL Version

curl --version

Fetch a Webpage

curl https://example.com

Save Output to a File

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

Follow Redirects

curl -L https://example.com

Show HTTP Response Headers

curl -I https://example.com

  1. cURL with HTTP Methods

cURL allows you to make HTTP requests using different methods.

GET Request

curl -X GET https://api.example.com/data

POST Request (Sending Data)

curl -X POST -d "name=John&age=30" https://api.example.com/users

PUT Request (Updating Data)

curl -X PUT -d "name=John Doe" https://api.example.com/users/1

DELETE Request

curl -X DELETE https://api.example.com/users/1

  1. Sending Headers and Cookies

Sending Custom Headers

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

Sending Cookies

curl -b "session=abc123" https://example.com

  1. Handling Authentication with cURL

Basic Authentication

curl -u username:password https://api.example.com/login

OAuth Token Authentication

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" https://api.example.com/data
  1. Uploading and Downloading Files

Download a File

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

Upload a File

curl -X POST -F "file=@/path/to/file.txt" https://api.example.com/upload

  1. Working with JSON and APIs

Sending JSON Data

curl -X POST -H "Content-Type: application/json" -d '{"name": "John", "age": 30}' https://api.example.com/users

Fetching JSON Data

curl -H "Accept: application/json" https://api.example.com/data

  1. Handling SSL/TLS Certificates

Ignore SSL Certificate Validation

curl -k https://example.com

Use a Custom Certificate

curl --cacert /path/to/cert.pem https://secure.example.com

  1. Debugging with cURL

Enable Verbose Mode

curl -v https://example.com

Show Request and Response

curl -i https://example.com

Log cURL Details

curl -o output.txt -s -w "%{http_code}\n" https://example.com

  1. Using cURL in Different Languages

PHP cURL Example

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://api.example.com/data");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$response = curl_exec($ch);
curl_close($ch);
echo $response;

Python cURL Example

import requests response = requests.get("https://api.example.com/data") print(response.text)

Bash Script Example

#!/bin/bash curl -X GET https://api.example.com/data

  1. cURL Alternatives

If cURL doesn't fit your needs, consider these alternatives:

Wget: Great for downloading files.

Postman: A GUI tool for API testing.

httpie: A user-friendly HTTP client.

  1. Conclusion

cURL is an essential tool for developers and system administrators. Whether you're making API requests, automating tasks, or debugging network issues, cURL provides flexibility and power.

If you're working with APIs frequently, mastering cURL can significantly improve your workflow. Try out the commands in this guide and explore its full potential!

Frequently Asked Questions (FAQs)

  1. What is the difference between cURL and Wget?

cURL is more versatile and supports multiple protocols, while Wget is optimized for downloading files.

  1. Can I use cURL in Windows?

Yes, you can install cURL on Windows using Chocolatey or download it from the official website.

  1. How do I save cURL output to a file?

Use the -o flag:

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

  1. How do I debug cURL requests?

Use -v (verbose) mode:

curl -v https://example.com