IF EXISTS Command Exhibits Different Behavior on HPFS (97841)
This article was previously published under Q97841
Testing for the existence of a remote drive or directory via the IF
EXISTS drive:\nul command exhibits different behavior on an HPFS
partition than it does on a FAT partition. On an HPFS system, the IF
EXISTS command always returns FALSE when testing for the NUL device.
if exist %1\NUL goto dir_ok
echo %1 doesn't exist
echo %1 exists
The code returns "P: doesn't exist," but if P is an HPFS partition
linked to a sharename on a FAT partition, then the code returns "P:
exists." If you substitute the local hard drive for P, then the
command works as expected.
FAT and HPFS partitions respond differently to the IF EXISTS NUL
from an MS-DOS workstation, but not if you copy EXIST.BAT to
EXIST.CMD and run it from both types of partitions while at the
This behavior exists because of design differences in the two file
systems. In the FAT file system, the NUL device is one associated
with each partition, as well as each directory on that partition.
On an HPFS partition, however, the NUL device does not live as part
of the file system on the disk, and as such cannot be tested for
via the IF EXISTS from a remote client. Nevertheless, the device
does exist, and behaves identically to the implementation on FAT.
The following batch file shows an alternative way to test for the
existence of a remote drive/directory:
copy c:\config.sys %1\$$$$$.tst
if exists %1\$$$$$.txt goto dir_there
echo %1 does not exist!
echo %1 does exist!
Also, using the LAN Manager PTK, it is possible to programatically
test for the existence of a remote drive/directory.
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