This is a simple proof of concept showing how you can execute arbitrary commands to run on a web server, from the browser.
This is a terrible idea, except when it's not, so use this example carefully!
Read more about it here: https://www.codingblocks.net/programming/streaming-cmd-output-with-signalr/
Also, if you like .NET....
This was done as part of the 3rd Annual Advent of C#, 25 days worth of blog posts all about C#. Even better, there are two posts a day and 3 years to catch up on so you better hurry up and start reading!