INT 21 - DOS 2+ - "DUP2", "FORCEDUP" - FORCE DUPLICATE FILE HANDLE
AH = 46h
BX = file handle
CX = file handle to become duplicate of first handle
Return: CF clear if successful
CF set on error
AX = error code (04h,06h) (see AH=59h)
Notes:  closes file with handle CX if it is still open
DOS 3.30 hangs if BX=CX on entry
moving file pointer for either handle will also move it for the other,
because both will refer to the same system file table
SeeAlso: AH=45h

See also: 213D

2146 - DOS 2+ - "DUP2", "FORCEDUP" - FORCE DUPLICATE FILE HANDLE