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cURL

curl (short for "Client URL") is a command-line tool and library for transferring data with URLs. It supports various protocols, including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, LDAP, and more. curl is widely used to interact with web services, download files, and perform data transfers from the command line in Unix-like operating systems.

Basic Syntax​

curl [options] [URL]

Common Options​

  • -O or --remote-name: Save the downloaded file with the remote file name.
  • -o or --output: Specify the output file name.
  • -L or --location: Follow redirects.
  • -I or --head: Fetch only the headers.
  • -s or --silent: Silent mode (no progress meter or error messages).
  • -A or --user-agent: Set the user agent string.
  • -X or --request: Specify HTTP request method.
  • -d or --data: HTTP POST data.
  • -H or --header: Add custom headers.
  • -u or --user: HTTP authentication credentials.
  • -k or --insecure: Allow connections to SSL sites without certificates.

Examples​

  1. Downloading a File:

    curl -O https://www.example.com/file.txt

    This downloads file.txt from example.com and saves it with the same name.

  2. Downloading with Custom Output Name:

    curl -o output.txt https://www.example.com/file.txt

    This downloads file.txt from example.com and saves it as output.txt.

  3. Following Redirects:

    curl -L https://www.example.com

    This follows redirects and fetches the content from the final URL.

  4. Fetching Only Headers:

    curl -I https://www.example.com

    This fetches only the headers of the web page.

  5. Sending POST Data:

    curl -X POST -d "key=value" https://www.example.com/post_endpoint

    This sends POST data to the specified endpoint.

  6. Adding Custom Headers:

    curl -H "Authorization: Bearer TOKEN" https://api.example.com/resource

    This adds a custom authorization header to the request.

  7. HTTP Authentication:

    curl -u username:password https://www.example.com/protected

    This performs HTTP basic authentication with the provided credentials.

  8. Ignoring SSL Certificate Verification:

    curl -k https://www.example.com

    This allows connecting to an SSL site without verifying the certificate.

Advanced Usage​

  • curl supports a wide range of options and can be used to upload files, send custom HTTP headers, handle cookies, and perform more advanced HTTP interactions.
  • curl is also available as a library and can be integrated into scripts and applications.

Use Cases​

  • Downloading files from the internet.
  • Interacting with RESTful APIs.
  • Testing web services and APIs.
  • Debugging network issues.
  • Automating tasks involving data transfer.

Conclusion​

curl is a powerful and flexible tool for interacting with web resources from the command line. Its wide range of features and support for various protocols make it a valuable tool for both casual users and developers.


✅ Resources​