The Something Terrible in this case is early DOS which did not have separate folders. So the device files were in the same namespace as the user's files, so the user couldn't name a file CON or LPT1. These are preserved for backwards compatibility. To this day you can write a program that writes to a CON file in any folder, and the program will print the write to console.

This has actually changed a bit in the last few years. In Windows 11 writing to `.\CON` will write to the file but writing to `CON` will still write to the console.

Another interesting aspect of this, which I remember specifically from reading MS-DOS manuals in the 90s as a kid (I was an incredibly fun 12 year old) is that this choice was an intentional one done in the name of flexibility. These device names were correctly written with a colon, but you are allowed to omit the colons. For instance:

copy con lpt1

And

copy con: lpt1:

were interchangeable. If they’d chosen to not save users keystrokes and force colons when referencing devices, I’m not positive, but I think it would have eliminated the need for many of these reserved words in file names in general.

Also, side note, the “copy con outputfilename.txt” idiom is one that I still can’t ever remember how to do the equivalent on UNIX/Linux!

> Also, side note, the “copy con outputfilename.txt” idiom is one that I still can’t ever remember how to do the equivalent on UNIX/Linux!

cat > outputfilename.txt

But it's not CTRL-Z to end, right? That's the part I forget every time :D

One of my favorite bbs sig tags was "REAL programmers use COPY CON FILE.EXE"

> What are you doing with this user-supplied input?

Creating Sharepoint shares which can be mounted as network shares in Windows where these filenames are not allowed?

I thought this as well but there's plenty of dangerous commands that aren't escaped here. I'm assuming it's a limitation of it actually writing something to the filesystem, hopefully your own (with the desktop app) and not one in Azure.

> I was about to say

Yet you said it twice[1].

[1] https://news.ycombinator.com/item?id=37076913