Master the Curl Command in Linux with 15 Examples

The curl command in Linux is a tool for transferring data using various protocols. It allows users to download, upload, and manage files efficiently through simple command-line instructions.

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The curl command in Linux is used for transferring data across a network using various protocols such as HTTP and FTP. It enables users to easily download and upload files through command-line interactions. This command is essential for developers to manage data transfers efficiently, support testing, and automate network tasks.

Brief History of the curl command

In the mid-1990s, Daniel Stenberg, a Swedish programmer, began developing the Curl project. This initiative aimed to create a bot that periodically downloaded exchange rates, providing the Swedish krona equivalent in US dollars to IRC users. Over time, Curl evolved significantly as more protocols and features were introduced, resulting in the comprehensive curl command we use in Linux distros today.

Curl Command in Linux with 15 Practical Examples

Below, I provide 15 essential use cases of the curl command to efficiently manage data in Linux, particularly beneficial for developers:

1. Show Curl Version

Use the -V or --version option to display the version, supported protocols, and features of the installed curl command.

Example:

$ curl --version

2. Download a File

The -O option allows you to download and save a file in your current directory with its original name. To rename it, use the -o option. These options help in maintaining organized data storage.

Examples:

$ curl -O http://yourdomain.com/yourfile.tar.gz

$ curl -o newfile.tar.gz http://yourdomain.com/yourfile.tar.gz

3. Continue a Discontinued Download

Resuming incomplete downloads with -C - prevents data loss and saves time by continuing from where the download was interrupted.

Example:

$ curl -C - -O http://yourdomain.com/yourfile.tar.gz

4. Download Multiple Files

Using xargs with curl to download files listed in a text file optimizes batch processing, reducing manual download efforts.

Example:

$ xargs -n 1 curl -O < listurls.txt

5. Use a Proxy with Authentication

For secure data transfers via a proxy server, specify proxy details with -x and authenticate with -U if needed. This ensures controlled access to resources.

Example:

$ curl -x proxy.yourdomain.com:8080 -U user:password -O http://yourdomain.com/yourfile.tar.gz

6. HTTP Header Query

Retrieving HTTP headers using -I offers insights into server responses, aiding in web server communications and debugging.

Example:

$ curl -I host.linux-zone.org

7. Create a POST Request with Parameters

Simulate HTML form submissions with the --data option, useful for testing web forms and applications.

Example:

$ curl --data "firstName=John&lastName=Doe" https://yourdomain.com/info.php

8. Download from an FTP Server with Authentication

Download files securely from FTP servers using -u to provide authentication, essential for accessing protected data.

Example:

$ curl -u username:password -O ftp://yourftpserver/yourfile.tar.gz

9. Upload Files to an FTP Server

Upload files to an FTP server efficiently with -T , facilitating easy file management and transfers.

Example:

$ curl -u username:password -T mylocalfile.tar.gz ftp://yourftpserver

10. Specify a User-Agent

Change the user-agent string with --user-agent to test client-server interactions and browser emulations.

Example:

$ curl -I http://localhost --user-agent "I am a new web browser"

11. Save Cookies from a Website

Use --cookie-jar to store cookies, allowing for session persistence in subsequent visits.

Example:

$ curl --cookie-jar cnncookies.txt https://www.cnn.com/index.html -O

12. Send Website Cookies

Reuse stored cookies with --cookie to maintain session continuity, enhancing user experience and testing accuracy.

Example:

$ curl --cookie cnncookies.txt https://www.cnn.com

13. Resolve Domain Names Locally

Local domain testing with --resolve before going live is critical for verifying server configurations and avoiding DNS complications.

Example:

$ curl --resolve www.yourdomain.com:80:localhost http://www.yourdomain.com/

14. Limit Download Speed

Regulate bandwidth usage with --limit-rate , preventing curl from overconsuming resources and maintaining network stability.

Example:

$ curl --limit-rate 100K http://yourdomain.com/yourfile.tar.gz -O

FAQ:

curl -u username:password -T localfile ftp://server

Conclusion

In this article, I have provided a concise overview of the curl command in Linux with 15 practical examples. These tools and techniques can significantly improve your data management and development processes.

Do you know any other curl commands that may not be mentioned in this article? Be comfortable with us and share it in the comments section. Also, if you have a question, ask it. We are waiting for you.