cURL

Back in the day you could use a computer unless you knew command line, but all that is changed now thanks to the GUIs. Although not mandatory, commands are still used nowadays to get things done faster and some of the most powerful tools out there still rely on it.

cURL is a command line tool that has the role of helping you transfer data to and from various web servers. Since the tool is scriptable and versatile, it can be configured to perform complex data transfer operations. If you need something simpler that involves rather minimalistic tasks, then wget may be a better option.

Considering that one of the primary roles of the program is to communicate with web servers, it means it is an ideal candidate for testing APIs, managing cURL compatible apps and web scraping. As far as the latter is concerned, there are some websites out there that provide data to curl.

While it has many uses, the main one is to test APIs, as you can easily send and receive responses via the tool. Providing that you are authenticated, you can send GET and POST requests from various API endpoints.

Functionality-wise, the best way to describe the tool is a non-interactive browser. Unlike Firefox or Chrome that render the information by default, the app pulls the information from the web and displays it in your terminal. If necessary, you can save the data in a file.

Lastly, it is worth mentioning that cURL comes with extensive support for a wide array of protocols, so you may use it with all sorts of connections, including, but not limited to POP3, IMAP, Telnet, HTTPS, FTPS or SCP. On a side note, if no protocol is provided, then the app will use HTTP by default.