Curl: Data Transfer and API Interaction

The curl command is a powerful command-line tool used for transferring data from or to a server. It supports various protocols, making it indispensable for developers for tasks ranging from downloading files to interacting with RESTful APIs.

The basic syntax for curl is:

curl [options] [URL]

Common Curl Options

Option	Description
-o	Save the output to a file with a specified name.
-O	Save the output to a file using the same name as the remote file.
-C -	Resume a download from where it left off.
-I	Fetch only the HTTP headers of a URL.
-L	Follow HTTP redirects.

Curl Usage Examples

• Retrieve a webpage's content:

  curl example.com

• Save a webpage to a local file:

  curl example.com -o example.html

• Resume an interrupted download:

  curl -C - -O https://releases.ubuntu.com/21.10/ubuntu-21.10-desktop-amd64.iso

• Fetch only the headers of a URL:

  curl -I example.com

• Get weather information for a location:

  curl wttr.in/london

Handling REST API Calls with Curl

curl is widely used for making HTTP requests to interact with RESTful APIs. Here's how to perform common HTTP methods:

GET Requests

The GET method is used to fetch resources from a server. It is the default method in curl, so you often don't need to specify it explicitly.

Example of a GET request:

curl https://reqres.in/api/users/2

POST Requests

The POST method is used to create a new resource on the server. You typically send data in the request body.

To send a curl POST request, use the -X POST option and specify the content type and data using -H and -d respectively.

Example of a POST request to register a user:

curl -X POST -H "Content-Type: application/json" -d '{"email": "eve.holt@reqres.in","password": "pistol"}' https://reqres.in/api/register

PUT Requests

The PUT method is used to update an existing resource on the server. Similar to POST, you send data in the request body.

To send a curl PUT request, use the -X PUT option.

Example of a PUT request to update user information:

curl -X PUT -H "Content-Type: application/json" -d '{"name": "morpheus","job": "zion resident"}' https://reqres.in/api/users/2

DELETE Requests

The DELETE method is used to remove a resource from the server.

To send a curl DELETE request, use the -X DELETE option.

Example of a DELETE request:

curl -X DELETE https://reqres.in/api/users/2

For more advanced usage and options, refer to the official curl documentation.