INT 21h AH=3Ah: remove a directory — 8086 assembly guide

Remove an empty directory, the RD command. It fails if the directory holds anything or is the current directory of its drive.

INT 21h AH=3Ah removes the directory named by the ASCIIZ path at DS:DX: RD (RMDIR) at the prompt. It removes only an empty directory, one with no entries but "." and "..".

AX (CF = 1)	Why
3	path not found: there is no such directory
5	access denied: not empty, read-only, or the root directory
16 (10h)	it is the current directory of its drive

Hidden and system files count. DIR does not show them, so a directory can look empty and still fail with 5. To clear one, find its files with INT 21h AH=4Eh (with hidden and system bits in CX), clear a read-only attribute with INT 21h AH=43h, and delete each with INT 21h AH=41h; subdirectories have to be emptied and removed first.

No drive's current directory can be removed, not only the current drive's: change out of it first. The example goes into TESTDIR, tries to remove it from inside, then from its parent, then once more:

prints: rmdir while inside it: error 16 / rmdir from its parent: ok / rmdir once more: error 3

MOV     AH, 39h           ; make TESTDIR
MOV     DX, OFFSET DIR1
INT     21h
MOV     AH, 3Bh           ; and go into it
MOV     DX, OFFSET DIR1
INT     21h
MOV     DX, OFFSET INM1
MOV     AH, 09h
INT     21h
MOV     AH, 3Ah           ; DOS: remove the directory named at DS:DX
MOV     DX, OFFSET SELF1  ; "..\TESTDIR": where we are
INT     21h
CALL    RESULT            ; error 16
MOV     AH, 3Bh           ; up to the parent
MOV     DX, OFFSET UP1
INT     21h
MOV     DX, OFFSET OUTM1
MOV     AH, 09h
INT     21h
MOV     AH, 3Ah
MOV     DX, OFFSET DIR1
INT     21h
CALL    RESULT            ; ok
MOV     DX, OFFSET AGAINM1
MOV     AH, 09h
INT     21h
MOV     AH, 3Ah
MOV     DX, OFFSET DIR1
INT     21h
CALL    RESULT            ; error 3: it is gone
 
DIR1    DB      "TESTDIR", 0
SELF1   DB      "..\TESTDIR", 0
UP1     DB      "..", 0
INM1    DB      "rmdir while inside it: $"
OUTM1   DB      "rmdir from its parent: $"
AGAINM1 DB      "rmdir once more: $"
RESULT  PROC    NEAR      ; print "ok", or "error" and AX when CF = 1
PUSHF                     ; keeps AX and CF for the caller
PUSH    AX
MOV     DX, OFFSET OKMSG
JNC     RESULT1
MOV     DX, OFFSET ERRMSG
MOV     AH, 09h
INT     21h
POP     AX
PUSH    AX
CALL    PDEC              ; the error code
MOV     DX, OFFSET CRLF
RESULT1:
MOV     AH, 09h
INT     21h
POP     AX
POPF
RET
RESULT  ENDP
OKMSG   DB      "ok", 13, 10, "$"
ERRMSG  DB      "error $"
PDEC    PROC    NEAR      ; print AX in decimal (changes AX BX CX DX)
MOV     BX, 10
XOR     CX, CX            ; digits on the stack
PDEC1:
XOR     DX, DX
DIV     BX                ; AX = AX / 10, DX = the last digit
PUSH    DX
INC     CX
OR      AX, AX
JNZ     PDEC1
PDEC2:
POP     DX                ; the digits come back first to last
ADD     DL, "0"
MOV     AH, 02h
INT     21h
LOOP    PDEC2
RET
PDEC    ENDP
CRLF    DB      13, 10, "$"

DOSBox-X makes the error 16 check itself before it asks the host to delete the folder, since the host knows nothing about DOS's current directories. When the host refuses for another reason, DOSBox-X reports 5, as DOS does for a directory that is not empty.