To compile this, you execute the mono C# compiler:

mcs fileinfo.cs

Which should give us a file named fileinfo.exe -- it's interesting to note that because this file is in IL, it can be run on Windows as well.

Now you can just run the exe:

csharp-fileinfo# ./fileinfo.exe fileinfo.cs
Filename:  fileinfo.cs
Extension: .cs
Path to:   /home/mikal/opensource/csharp-fileinfo
Size:      762
Hash:      1783806388