AUX (including AUX.*, in any directory on Windows ) is a special “file” representing a hardware device (by default, tue first serial port, same as COM1); trying to copy to or from a file name matching that pattern results in accessing the device instead.

There are a bunch of these special files. [0]

[0] A list is deep on this page: https://docs.microsoft.com/en-us/windows/win32/fileio/naming...

For legacy reasons, any drive path that ends in a special name, such as `AUX` will be rewritten by Win32 as the NT path `\??\AUX`. This `AUX` is a special device, not a file on the filesystem.

So, for example, `C:\Users\ChrisSD\AUX` will be resolved to `\??\AUX`.

Even more surprisingly, any filename that starts with `aux.` will also be affected by this. E.g. `C:\Users\ChrisSD\aux.txt`.

Try saving any file as aux.txt in windows.