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Can DOSBox set the ErrorLevel on exit?

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First post, by RrnR

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I have DOSBox set up so that I can pass it command lines which previously were called directly from batch files (I call it from a wrapper batch file that checks to see if the platform is 64-bit - if it isn't, it just executes the command line, otherwise it fires up DOSBox and passes the command line to it - that way the batch files run on both 32 and 64-bit systems).

Anyway, these command lines usually invoke a build process that sets ErrorLevel according to success or failure. When the command line executes inside DOSBox, how can I pass the resulting ErrorLevel back to the process that invoked DOSBox when DOSBox exits?

Reply 3 of 12, by Qbix

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not sure if passing the emulated error code back to host is a good idea.
As there is not really a problem in dosbox itself if your application fails to find a file.

Water flows down the stream
How to ask questions the smart way!

Reply 5 of 12, by RrnR

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@Qbix I disagree. When you are using DOSBox essentially as a 32-bit command processor emulator for a single command line, then it makes the emulation more complete. I'm not suggesting it become a permanent feature, but a DOSBox.exe command line option like -SetErrorLevel.

@Malvineous I like your idea!

I just tried it however, and I can't see how to get ErrorLevel

echo %ErrorLevel% ><some path>\ErrorLevel.txt

doesn't work, as DOSBox doesn't set an environment variable to ErrorLevel. Any suggestions?

Reply 6 of 12, by collector

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DOSBox's emulation was never meant to be that complete or accurate. It is meant for compatibility with decent performance with DOS games. There are other emulators out there if you need more.

The Sierra Help Pages -- New Sierra Game Installers -- Sierra Game Patches -- New Non-Sierra Game Installers

Reply 7 of 12, by Joey_sw

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if you can access debug.exe that usually supplied with Microsoft OS, you can create a .COM executable file to output the Errorlevel.
My version should works if errorlevel are lower than 10.

0100  B44D          MOV     AH,4D
0102  CD21          INT     21
0104  88C2          MOV     DL,AL
0106  80C230        ADD     DL,30
0109  B402          MOV     AH,02
010B  CD21          INT     21
010D  B44C          MOV     AH,4C
010F  CD21          INT     21

you can make that .COM file using hex-editor program too.

B4 4D CD 21 88 C2 80 C2-30 B4 02 CD 21 B4 4C CD 21

Its depends if above int 21h functions were implemented in dosbox or not.
But it should works if you're booting using MS-DOS boot-image in dosbox.

-fffuuu

Reply 9 of 12, by Malvineous

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If DOSBox did set the errorlevel to an environment variable, then it would no longer be emulating DOS. The %errorlevel% environment variable wasn't added until cmd.exe came about. See ERRORLEVEL is not %ERRORLEVEL%.

Joey_sw's idea is very good, because otherwise I think you have to resort to something terrible like this, to keep within DOS compatibility:

IF ERRORLEVEL 0 ECHO 0 > E.TXT
IF ERRORLEVEL 1 ECHO 1 > E.TXT
IF ERRORLEVEL 2 ECHO 2 > E.TXT
...

Reply 10 of 12, by RrnR

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I don't see anything wrong with "not emulating DOS". Keeping the faith can be protected from additions to functionality like this by requiring a command line parameter when launching the program, e.g.

DOSBox.exe -AllowExtensions

If this wasn't present then DOSBox would behave as it does now. Developers would then be free to add other enhancements like the GEQ, LEQ, etc operators in IF statements.

Reply 11 of 12, by collector

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The emphasis of DOSBox will not change and pushing the point will only annoy the DOSBox devs. You might present this to the developers of either vDos or DOSBox-X.

The Sierra Help Pages -- New Sierra Game Installers -- Sierra Game Patches -- New Non-Sierra Game Installers

Reply 12 of 12, by MtheK2

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  FYI

  I have a simple way to get the feature, the Environment Variable %errorlevel%
that DOSBox-x doesn't seem to want to give us, by merely enhancing the usage of
the previously-supplied 16bit program that gets the previous RC (return code). 

  As B 4, this does NOT need so many fixed RCs using ECHO and a file to determine
it, and certainly not a different "hypervisor"/emulator, as follows:


1. make a 16-bit MASM program (or use the previously-supplied program for up to 10)
to create a .log file from STDOUT re-direction. Partial code:

 006A 0000			DBLWRD   WORD  ?
 006C 00			SAVERC   BYTE  ?

 006D  0003 [			CNTNUM   BYTE  3 DUP('0')
        30
       ]
 0070 0D			RECEND   BYTE  0Dh
 0071  0A			         BYTE  0Ah     

 0000				        .CODE

				        .STARTUP                   ; prime regs properly

 001F  B4 4D			         MOV   AH,4Dh              ; get prev return code in AL (8bit only)
 0021  CD 21			         INT   21h
 0023  A2 006C R		         MOV   SAVERC,AL

 0026  B4 00			         MOV   AH,0
 0028  BB 006D R		         MOV   BX,OFFSET CNTNUM+0
 002B  BA 0000			         MOV   DX,0
 002E  C7 06 006A R 000A	         MOV   DBLWRD,10
 0034  F7 36 006A R		         DIV   DBLWRD              ; divide by 10
 0038  83 C2 30			         ADD   DX,0030h
 003B  88 57 02			         MOV   [BX+2],DL    ; move remainder (3rd digit)  
 003E  BA 0000			         MOV   DX,0
 0041  C7 06 006A R 000A	         MOV   DBLWRD,10
 0047  F7 36 006A R		         DIV   DBLWRD              ; divide by 10
 004B  83 C2 30			         ADD   DX,0030h
 004E  88 57 01			         MOV   [BX+1],DL    ; move remainder (2nd digit)  
 0051  83 C0 30			         ADD   AX,0030h
 0054  88 07			         MOV   [BX+0],AL    ; move quotient  (1st digit)

				; send to STDOUT (re-directed to file)...         

 0056  8A 16 006D R		         MOV   DL,CNTNUM+0
 005A  B4 02			         MOV   AH,02h
 005C  CD 21			         INT   21h
 005E  8A 16 006E R		         MOV   DL,CNTNUM+1
 0062  B4 02			         MOV   AH,02h
 0064  CD 21			         INT   21h
 0066  8A 16 006F R		         MOV   DL,CNTNUM+2
 006A  B4 02			         MOV   AH,02h
 006C  CD 21			         INT   21h 

 006E  8A 16 0070 R		         MOV   DL,RECEND+0
 0072  B4 02			         MOV   AH,02h
…Show last 67 lines
 0074  CD 21			         INT   21h  
 0076  8A 16 0071 R		         MOV   DL,RECEND+1
 007A  B4 02			         MOV   AH,02h
 007C  CD 21			         INT   21h  

 007E  A0 006C R		         MOV   AL,SAVERC
				;* AL contains the return code.

				        .EXIT

2. make a .txt file as follows (ie: in NOTEPAD):

set ERRORLEVEL=

Make sure the "invisible" CRLF (0D0Ah) is NOT(!!!) at the end of this line.
If you want a different EV set, you can either change the EV name to whatever
(ie: MyEnvVar) or save it to this new EV in step 5.

3. run the 16-bit program in step 1 in DOSBox-x after the program(s) to be 
checked, usually in place of something like 'set MyEnvVar=%errorlevel%':

call GETRCBOX.exe >GETRCBOX.log

The O/P .log file is the RC (only up to 255 as AL is only 8bit); ie:

001

and contains a CRLF at the end of the line.
The RC is also set normally, still available in ERRORLEVEL itself
(a la the previously-supplied program).

4. then run these commands after step 3:

type GETRCBOX.txt  >GETRCBOX.bat
type GETRCBOX.log >>GETRCBOX.bat

5. then run this newly-created .bat and a TYPE/ECHO command(s) after step 4:

rem    (if desired)...
type GETRCBOX.bat

call GETRCBOX.bat

rem    (if desired)...
set MyEnvVar=%errorlevel% 

rem    (if desired)...
echo RC=%errorlevel%          /or/     %MyEnvVar%

The RC is shown by DOSBox-x via the TYPE/ECHO command(s) O/P.

  Without this technique, the ECHO command shows no RC, as the EV doesn't "exist".
In a way, this kinda duplicates the real "echo RC=%errorlevel%" that is so
valuable in 32bit.

  You still have to code the individual ERRORLEVEL checks to do anything else; ie:

if ERRORLEVEL 2 GOTO EXECHIGH
if ERRORLEVEL == 1 GOTO EXECRC1              rem (or %MyEnvVar%)...
if ERRORLEVEL == 0 GOTO EXECRC0
GOTO EXECNEG

6. finally, after step 5 or so, clear the EV for next time (ie: no residue):

set ERRORLEVEL=

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