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Understanding curl

A dense, one-page guide on curl.

Loni

Loni

— 1 min read
Understanding curl
Photo by Sandy Millar / Unsplash

curl is a powerful command-line tool for transferring data to or from a server. curl supports a lot of protocols, including HTTP, FTP, and POP3. curl is a go-to utility for a variety of network operations.

Key Features

curl excels at downloading files, sending data, and managing server interactions. Its strength is its versatility in dealing with different data formats and different authentication methods. You can use curl to pull data from a remote location or to push data to a server, and it can do all of this using a variety of different network protocols.

This is a tool that's not just good at what it does, it can be used in most, if not all network environments.

Common Use Cases

  1. Downloading Files: Download files using curl http://example.com --output path/to/file. To save a file under its remote name, use curl --remote-name http://example.com/filename.
  2. Handling Redirects and Resuming Downloads: curl handles location redirects and resumes interrupted downloads. For instance, curl --fail --remote-name --location --continue-at - http://example.com/filename continues a previous download and returns an error on server issues.
  3. Sending Data: Submitting data is straightforward with curl --data 'name=bob' http://example.com/form. For JSON data, use curl --data '{"name":"bob"}' --header 'Content-Type: application/json' http://example.com/users/1234.
  4. Custom Headers and HTTP Methods: Modify requests with headers using curl --header 'X-My-Header: 123' --request PUT http://example.com.

Advanced Features and Edge Cases

  • Authentication: Pass credentials with curl --user username http://example.com.
  • Certificates and Insecure Connections: Handle certificates via curl --cert client.pem --key key.pem --insecure https://example.com.
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Be aware of less common, but important scenarios, like proxy handling, and content type management.

Conclusion and Additional Resources

curl is a tool of remarkable flexibility, indispensable for handling a wide array of data transfer tasks. Its utility spans from simple file downloads to complex data interaction across various protocols. For more exploration, especially into its less common options and functionalities, refer to the official curl documentation at https://curl.se/docs/manpage.html.

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