How do I remove a file named "NUL" on Windows?

Try

Del \\?\C:\My\Path\NUL

in the command prompt.

See this Microsoft Support article for details: You cannot delete a file or a folder on an NTFS file system volume, under "Cause 5: The file name includes a reserved name in the Win32 name space".

Alternatively if you have Cygwin installed, you may want to know, that it has no problem with such files or folders. Particularly,

rm -r /cygdrive/c/path/to/the/file/or/folder/you/want/to/delete

typed in the Cygwin terminal deletes the file or folder named nul or a folder, containing it. This is also applicable to other special file names such as CON, PRN, AUX, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8.

I'm adding this here because it is high in the google results and I had a similar issue for a folder named NUL. Unfortunately the above fixes didnt help. Neither did a ton of other stuff I looked at.

I tried rmdir\\?\C:\My\Path\NUL and rmdir\\.\C:\My\Path\NUL without any success and also tried several commands using bash from my SourceTree installation. No joy.

In the end I used DIR /X /A from cmd to list the short names in the parent directory. This returned NUL~1 for my NUL folder.

This was then used in the standard command rmdir /s NUL~1 and finally fixed the problem.