Re: Get dos errorlevel

 BBS: Inland Empire Archive
Date: 02-16-94 (16:03)             Number: 155
From: GARY GLUECKERT               Refer#: 136
  To: FLOYD HOBSON                  Recvd: NO  
Subj: Re: Get dos errorlevel         Conf: (2) Quik_Bas
FH>check for the errorlevel<G>.  There doesn't appear to be a clean way
FH>to do this - my workaroud has been to call the child via a batch file
FH>that creates a nul length semaphore file to reflect the error level,
FH>then delete the nul file after determining the error level.

I found a public domain ASM object file that can be linked into QB4.x,
BASIC 7.x programs which does this so now we can go and do it cleanly
<g>. If you study the code below you will see how it's done and perhaps
you can write the Int calls in BASIC (but why bother if they are in

; MonitorShell (MONSHELL.ASM)

; Written by Tony Elliott

; EllTech Development, Inc.
; 4374 Shallowford Industrial Parkway
; Marietta, GA 30066
; (404) 928-8960 Voice or (404) 928-7111 BBS (HST)

; Released into the public domain.

; This routine is written for Microsoft QuickBASIC 4.x, BASIC 6.x and
Microsoft ; PDS 7.x. Assemble using MASM 5.1:  MASM MONSHELL;

; You can link it directly to your program, place it in a LINK library
(.LIB) ; or a .QLB.

; To use it:

;   DECLARE SUB MonitorShell ()
;   DECLARE FUNCTION FetchErrorLevel% ()
;   CALL MonitorShell
;   SHELL "PkZip -Xxy"
;   PRINT "ErrorLevel returned from SHELL:";FetchErrorLevel

.model medium, basic

Old21        Label Dword        ;Label pointing to old Int 21h handler
Old21Offset  dw ?               ;Offset part
Old21Segment dw ?               ;Segment part
MonitorSet   db 0               ;Our "hooked" flag
ExitCode     db ?               ;Where we store the exit code

MonitorShell proc uses ds

    ; From BASIC: CALL MonitorShell

    cmp cs:MonitorSet,0         ;Are we already hooked?
    jnz MonitorExit             ;If so, exit
    mov ax,3521h                ;Get current vector for int 21h
    int 21h
    mov cs:Old21Segment,es      ;Remember it for later
    mov cs:Old21Offset,bx
    mov ax,2521h
    push cs
    pop ds                      ;Point int 21h handler to our code
    mov dx, offset OurInt21
    int 21h
    mov cs:MonitorSet,-1        ;Set our flag


OurInt21:                       ;Our Int 21h handler
    cmp ah,4ch                  ;Is it a 'terminate' request?
    jnz Continue                ;If not, continue on

    mov cs:ExitCode,al          ;Remember the exit code
    push ax
    push ds
    mov ax,2521h                ;Unhook ourself after the first hit
    mov ds,Old21Segment
    mov dx,Old21Offset
    int 21h                     ;Point Int 21h back to original handler
    pop ds
    pop ax
    mov cs:MonitorSet,0         ;Set out flag back to zero

    jmp dword ptr [Old21]       ;Transfer control to original Int 21h

MonitorShell endp

FetchErrorLevel proc

    ;From BASIC: DECLARE FUNCTION FetchErrorLevel%
    ;            PRINT "Last errorlevel:"; FetchErrorLevel%

    mov al,cs:ExitCode          ;Put the errorlevel into al
    xor ah,ah                   ;Zero ah
    ret                         ;ErrorLevel returned as result

FetchErrorLevel endp

If you don't have the MASM compiler to create the .OBJ file you can
FREQ the entire package from 1:107/270 with the magic name MONSHELL,
This goes for all others... help yourself.

Thanks to Tony Elliott for this great little helper!
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