INT 21 - DOS 2+ - "DUP" - DUPLICATE FILE HANDLE
AH = 45h
BX = file handle
Return: CF clear if successful
AX = new handle
CF set on error
AX = error code (04h,06h) (see AH=59h)
Notes:  moving file pointer for either handle will also move it for the other,
because both will refer to the same system file table
for DOS versions prior to 3.3, file writes may be forced to disk by
duplicating the file handle and closing the duplicate
SeeAlso: AH=46h

See also: 213D

2145 - DOS 2+ - "DUP" - DUPLICATE FILE HANDLE