Reversing Lines in a File

 Executive Summary:

To see what happened most recently first in text-based logs, you can use the Microsoft .NET Framework's class in both Windows Script Host (WSH) and PowerShell to create a simple reversal script.

I occasionally need to reverse the order of the lines in a text file. Reversal lets me see what happened most recently first in logs, and I can even use it to roll back complex changes such as extended file copy and move operations. No tool does this exact job in Windows, but you can use the Microsoft .NET Framework's Stack class in the System.Collections namespace to make your own tool. I'll demonstrate how to use the Stack class for reversal in both Windows Script Host (WSH) and PowerShell; when I'm done, you'll have tools usable in both the cmd.exe and PowerShell console environments.

The Need for LIFO
Let's talk about the way we typically see files and why reversing the order of their lines might be useful. Due to the way files are stored, we typically understand them as streams of data. The first item into the stream is the first out of the stream; the last item put into a stream is always at the tail end of the stream. This first-in, first-out (FIFO) processing model is called a queue. FIFO is the standard way that data is handled in most simple contexts such as reading, writing, and appending to files from a script. . . .