https://fd.lod.bz/redist/testing/devNUL/
NUL Device Existence Test
2023-05-23 

This test reveals two separate issues:

Issue 1:

	Testing for the existence of a path by using the NUL device does not
	work on CD/DVD drives or Network Shares. The result is always FALSE.

	IF EXIST N:\NUL ECHO Drive N: exists.

	See either result0.htm or result1.htm.

	Although this behavior deviates from that of other drives,it is 
	consistent with the behavior of MS-DOS 6.22 using MSCDEX. There is 
	the possibility that correcting this issue has the potential to break
	compatibility with any program that may rely on this behavior. 

Issue 2:

	Testing for the existence of a non-existing drive returns unreliable
	results. This seems reproducible based on the current working directory
	when the test is performed. For each test, a copy of the test.bat was
	placed in the current working directory.

	result0.htm was run with the current drive and directory on an internal
	local drive (C:) and incorrectly shows that the non-existing drive (P:)
	was found.

	result1.htm was run with the current drive and directory on an remote
	network share (N:) and correctly shows that the non-existing drive (P:)
	was not found.

	
	Switching back and forth between drive C: and N: and running the 
	TEST.BAT consistently produces the same results.