Int 21 Fn 4D  - DOS 2+ - Get Return Code (errorlevel)                      [D]

   AH = 4Dh

Return: AH = termination type
       00h normal (INT 20,INT 21/AH=00h, or INT 21/AH=4Ch)
       01h control-C abort
       02h critical error abort
       03h terminate and stay resident (INT 21/AH=31h or INT 27)
   AL = return code

Notes: the word in which DOS stores the return code is cleared after being
     read by this function, so the return code can only be retrieved once
   COMMAND.COM stores the return code of the last external command it
     executed as ERRORLEVEL
   this call should not be used if the child was started with AX=4B04h;
     use AH=8Ah instead
   the following sequence will close a Virtual DOS Machine under OS/2 2.0:
     MOV   AH,4Dh
     INT   21h
     HLT
     DB    02h,0FDh
     This sequence is the only way to close a specific VDM which was
     booted from floppy or a disk image.

See Also: AH=4Bh,AH=4Ch,AH=8Ah