How do I use curl?

Curl is a command-line tool that transfers data with URLs. Essentially, it's like a web browser, but instead of displaying a webpage visually, it shows you the raw data that the web server sends back. To use it, you generally open your terminal or command prompt and type curl followed by the URL you want to access.

Basic Usage

The most fundamental way to use curl is to retrieve the content of a web page:

curl https://www.example.com

This command will fetch the HTML source code of https://www.example.com and display it directly in your terminal. It's the equivalent of viewing the source code of a webpage in your browser.

Common Options and Examples

Curl offers a wide range of options to customize your requests. Here are some of the most common:

• -I or --head: Retrieves only the HTTP headers of the response. This is useful for checking server status, content type, or other metadata without downloading the entire page.

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

• -v or --verbose: Provides verbose output, showing you details about the request and response, including headers, connection information, and more. This is invaluable for debugging.

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

• -o or --output: Saves the output to a file instead of displaying it in the terminal.

  curl -o example.html https://www.example.com

  This saves the HTML of https://www.example.com to a file named example.html.

• -X or --request: Specifies the HTTP request method (e.g., GET, POST, PUT, DELETE). The default is GET. To make a POST request:

  curl -X POST https://www.example.com/api/endpoint

• -d or --data: Sends data in a POST request. Used with -X POST.

  curl -X POST -d "param1=value1&param2=value2" https://www.example.com/api/endpoint

• -H or --header: Adds a custom header to the request. Useful for setting content types, authorization tokens, or other request-specific information.

  curl -H "Content-Type: application/json" -X POST -d '{"key": "value"}' https://www.example.com/api/endpoint

• -u or --user: Provides authentication credentials (username and password).

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

Examples in a Table

Command	Description
curl https://www.example.com	Fetches the content of the website.
curl -I https://www.example.com	Retrieves only the HTTP headers.
curl -o myfile.html https://www.example.com	Saves the website content to myfile.html.
curl -X POST -d "name=John" https://api.example.com	Sends a POST request with data to the API endpoint.
curl -H "Authorization: Bearer TOKEN" https://api.example.com	Sends a request with an authorization header.

Advanced Usage and Considerations

Curl is a powerful tool with many more features, including support for cookies, proxies, SSL certificates, and more. Refer to the curl man page (man curl in your terminal) for a complete list of options. Security is important when using curl, especially when sending sensitive data. Always use HTTPS to encrypt communication and be cautious about storing or displaying authentication credentials.

In summary, curl is a versatile command-line tool that allows you to make HTTP requests and retrieve data from web servers. Understanding its basic usage and options opens up a wide range of possibilities for testing APIs, automating tasks, and debugging web applications.