Int 21H, AH=4DH

2 and higher

GET RETURN CODE (ERRORLEVEL)

AH = 4Dh

 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
CF clear

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 SVC function 2 will close a Virtual DOS Machine under OS/2 2.0+. This call is the only way to close a specific VDM which was booted from floppy or a disk image.

AH=4Bh,AH=4Ch

Text based on Ralf Brown Interrupt List Release 61