How to Use cURL to Download Files: A Comprehensive Guide

cURL is a powerful, open-source command-line tool that allows you to transfer data. In this comprehensive guide, we ‘ll tell you the process of using cURL to download files, covering everything from basic downloads to more advanced operations. By mastering these techniques, you’ll enhance your ability to handle file downloads in an automated and reliable manner.

What is cURL?

cURL is an open-source command-line tool that supports data transfer over various protocols such as HTTP, FTP, and SMTP. It can be used for file download management, remote control, and is often combined with Python for automation tasks.

Why use cURL to download files?

As a free open-source tool, cURL can fetch and transfer web data and is often used for web debugging. It offers the advantages of being free and easy to use.
cURL is very powerful, and mastering the cURL command line can help software developers with their daily tasks.

Basic File Download

Using the original filename

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

For example, let’s demonstrate how to use the cURL command to download a file from the example website:
The -O (uppercase) option instructs cURL to save the file with the same name as the URL.

Managing Filenames with cURL

If you want to save the file with a custom filename, use the -o (lowercase) option.

curl -o newfile.zip https://thordata.com/file.zip

Handling Redirects

When using cURL to access an HTTP website and encountering status codes 301, 302, or 303, by default cURL will not follow the redirect page information. You will need to use a command to request the URL again.
For detailed status code explanations: MDN Web Docs

Status Code	Meaning	Common Use Case
301	Moved Permanently	URL changed, SEO redirect
302	Found (Temporary Redirect)	Temporary redirect (e.g., page maintenance)
303	See Other	Form submission redirect to prevent resubmission

Check Response Headers (including status codes)

curl -I https://example.com

View the full response

This shows detailed request and response information, including the status code and the target URL for redirection.

curl -v https://example.com

Using the -L option to handle redirects

curl -L https://example.com

Automatically handling redirects and downloading the file

You can combine the -L option and the -O (save file) option, so that when a file is redirected, cURL will automatically download the file.
The -O option saves the downloaded file with its original filename.

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

Rate Limiting

curl --limit-rate 100k -O https://example.com/file.zip

The –limit-rate 100k option limits the download speed to 100KB/s.

Silent Download

A silent download typically refers to downloading a file without displaying any output such as progress bars, error messages, or other log data. It’s commonly used for automation scripts, background tasks, or when you don’t want to disrupt the user.

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

The -s or –silent flag enables silent mode, meaning no progress bars, error messages, etc., will be shown.
The -O option saves the file with the same name as the URL.

Authentication

Basic authentication is the most common HTTP authentication method, which typically requires a username and password. The server verifies these credentials to confirm the request’s legitimacy.

curl -u username:password -O https://example.com/protectedfile.zip

The -u username:password option is used to provide the username and password.
The -O option saves the file with the same name as the URL.

Download via Proxy

curl -x http://v****.pr.thordata.net:8080 -O https://example.com/file.zip

Advanced Operations with cURL Command for Downloading Files

Resuming Downloads

When a file download is interrupted, you can use cURL to resume downloading.

curl -C - -O https://example.com/largefile.zip

The -C – option tells cURL to continue downloading the file from where it was interrupted, and the -O option saves the file with its original filename.

Downloading Multiple Files

You can download multiple files by calling curl multiple times, or by placing multiple file URLs in a text file.

Method 1: Calling curl multiple times

curl -O https://thordata.com/file1.zip

curl -O https://thordata.com/file2.zip

Method 2: Place multiple file URLs in a text file and use xargs

echo -e "https://example.com/file1.zip\nhttps://thordata.com/file2.zip" | xargs -n 1 -P 2 curl -O

Displaying the Download Progress Bar

By default, cURL displays a progress bar showing the download progress. If you need more detailed progress information (such as download speed, size, etc.), you can use the –progress-bar flag:

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

Common cURL Command Examples

Command Example	Purpose and Action
-O	Downloads the file and saves it with the URL’s original filename.
-o	Specifies a custom filename for the downloaded content.
-I	View the HTTP response headers.
-v	Display detailed request and response information.
-L	Handle redirects with the -L option.
-s	Enable silent mode (no output).
-k	Ignore SSL certificate verification (useful for self-signed certificates).
-x	Set the proxy server.
–progress-bar	Show the download progress bar.
–limit-rate	Limit download speed.

For more cURL command-line options, check the manual: cURL Manual

Differences between cURL and wget

Both cURL and wget can be used to download files, but they have some differences.

Functionality: cURL excels at handling various HTTP request types (e.g., GET, POST). Wget primarily focuses on downloading files from the internet.

Command Parameters: cURL requires the -o parameter to specify a file for downloading, whereas wget does not require parameters to download a file directly.

For simple one-off file downloads, both tools can be used. However, for complex data exchange tasks, cURL is usually recommended. For downloading large, static resources efficiently, wget may be a better choice.

Common Errors and Best Practices

Not Handling Redirects: Failing to handle HTTP redirects during file downloads can cause downloads to fail, especially if the target URL has changed. The best practice is to use -L to redirect cURL to the target site.

Not Using -O or -o to Specify Filenames: This can lead to cURL saving files with default names instead of custom ones.

Not Handling Failures or Errors: If the server returns a 404 error or other failures, cURL will continue attempting to access the error message. The correct approach is to use -f to stop the download when cURL encounters an error.

Not Considering Bandwidth Limitation for Large Files: For large file downloads, setting an appropriate bandwidth limit can prevent disruption to other network activities. Use the –limit-rate option to control download speed.

Conclusion

This article introduced how to use cURL to download files, covering everything from basic downloads to advanced operations. Through this guide, you’ll learn how to manage filenames, handle redirects, perform authentication, limit download speed, and avoid common errors.