Unreliable IF EXIST NUL

[shidel]

Hi,

Here are two separate issues when using IF EXIST ?:\NUL. I'm lazy and wrote up a info text file over at https://fd.lod.bz/redist/testing/devNUL/ that I will just paste in here. The test batch and result files referenced in the text can be found there as well.

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NUL Device Existence Test

https://fd.lod.bz/redist/testing/devNUL/
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:). It 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:). It 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.