Finding missing and duplicate lines in text files using PowerShell

Every now and then I need to investigate bugs that get exposed because countable "things" are less or more than expected. In my special case I was dealing with an application that manages subscription handles to memory registers of programmable logic controllers (PLC). These programs are called Data Access Servers. Occasionally we get calls form customers reporting that the number of handles is less, or sometimes more than expected. The first step to debug this situation is to find out, which handles are missing or which ones are duplicates. This blog post describes how PowerShell's Compare-Object cmdlet makes this task, which used to be a pain in the "peep" now a piece of cake.