Testing for DEVICE NAMES

As stated in the CONDITION topic, EXIST always succeeds for a file. Some files
that always exist in every directory are the device names, including NUL, AUX, 
and PRN. Files that are device names cannot be deleted or COPYed, so it is
possible for an IF test to determine whether X (which may be an environment 
variable, replaceable parameter, or explicit FOR loop-variable) is a device
name. For example:

    IF EXIST X DEL X
    IF EXIST X ECHO X is a device name or a read-only file

    DEL FUNNYFIL
    IF EXIST X COPY X FUNNYFIL
    IF EXIST X IF NOT EXIST FUNNYFIL ECHO X is a device name or 0-length file

    MD FUNNYDIR
    IF EXIST FUNNYDIR\X ECHO X is a device name
    RD FUNNYDIR

Any non-existent file or directory name can be used in place of FUNNYFIL and 
FUNNYDIR, above.
