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Table of contents
1.
Introduction 
2.
Curl Command in Linux
3.
Syntax
4.
Using Curl with URLs
5.
Understanding the Progress Meter
6.
Exploring Curl's Options
7.
Frequently Asked Questions
7.1.
Can curl download multiple files at once?
7.2.
How does curl handle secure connections?
7.3.
Is it possible to resume a download with curl?
8.
Conclusion
Last Updated: Mar 27, 2024
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Curl Command in Linux

Author Sinki Kumari
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Introduction 

In the digital era, the effective management & interaction with web resources has become crucial. Whether it's downloading files, querying APIs, or testing web applications, the tools we use significantly streamline these tasks. One such tool, often overlooked yet incredibly powerful, is the curl command in Linux. This command-line utility is a versatile way to communicate with servers & retrieve data. 

By the end of this article, you'll gain a solid understanding of curl, including its syntax, how to use it with URLs, interpret its progress meter, and explore its various options. Let's embark on this journey to master the curl command & elevate your Linux skills.

Curl Command in Linux

curl, short for Client URL, is a command-line tool available on Linux & other Unix-like operating systems. It's used to transfer data to or from a server using supported protocols like HTTP, HTTPS, FTP, and more. One of its primary uses is in web development & testing, where it helps in sending requests & receiving responses without a graphical interface.

For example, if you want to download a file or query an API, curl provides a straightforward way to accomplish this from the command line. This makes it an indispensable tool for developers, especially when working with server-side applications or when a GUI is not available.

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Syntax

The basic syntax of the curl command is:

curl [options] [URL...]


Here, [options] are the various flags or parameters you can pass to modify the behavior of curl, and [URL...] is the address of the server or the resource you want to interact with.

For instance, a simple curl command to retrieve the contents of a webpage would look like this:

curl https://www.example.com


This command will output the HTML content of www.example.com to your terminal.

Using Curl with URLs

Understanding how to use curl with URLs is essential for effective data transfer. The URL in a curl command specifies the target resource on the internet or a local network. curl can handle a variety of URL formats, allowing you to interact with different types of servers and protocols.

For instance, to download a file from a server, you would use:

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


This command tells curl to download the file from the specified URL. The -O option instructs curl to save the file with its original name.

Moreover, curl is often used for testing APIs. For example, to make a GET request to an API, you can use:

curl https://api.example.com/data


This will fetch data from the API endpoint and display it in the terminal.

Understanding the Progress Meter

When you download large files or data, curl displays a progress meter in the terminal. This meter provides valuable information such as the amount of data transferred, transfer speed, and estimated time left.

For example, during a file download, you might see:

  Total  Received %  Xferd  Average Data Load  Average Speed Upload  Time Total Time  Current Time  Left

 Current

Speed

100  150M  100   150M 0 0 10.5 0  0:00:14    0:00:14  0 11.2M

This indicates the total size of the file (150M), the percentage completed, the average download speed (10.5M/s), and the time taken so far.

Exploring Curl's Options

curl comes with a wide range of options that modify its behavior. Some commonly used options include:

  • -o or --output [file_name]: Save the output to a file instead of displaying it.
     
  • -X or --request [command]: Specify a custom request method (like GET, POST, PUT).
     
  • -H or --header: Add extra headers to the request.
     
  • -d or --data: Send data in a POST request.
     
  • -u or --user: Provide username and password for server authentication.
     

Here's an example using some of these options:

curl -X POST -d "param1=value1&param2=value2" -H "Content-Type: application/x-www-form-urlencoded" https://api.example.com/post


This command makes a POST request with data and includes a header specifying the content type.

Frequently Asked Questions

Can curl download multiple files at once?

Yes, curl can download multiple files simultaneously. You can use a command like curl -O URL1 -O URL2 to download files from multiple URLs in a single command.

How does curl handle secure connections?

curl supports HTTPS and can handle secure connections. Use the https:// prefix in your URL to ensure a secure connection.

Is it possible to resume a download with curl?

Absolutely! You can resume a download using the -C - option with curl, which continues the download from where it was interrupted.

Conclusion

This article discusses the curl command in Linux, a powerful tool for transferring data using various protocols. We've covered its basic syntax, the significance of using it with URLs, the utility of the progress meter, and explored its myriad options. Armed with this knowledge, you're now well-equipped to utilize curl effectively in your projects and tasks, enhancing your efficiency and skillset in the Linux environment. Remember, practice is key to mastering any new tool, so feel free to experiment with curl and discover its full potential.

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