Obtain ERRORLEVEL value? Possible?

[Donald Darden]

Most child processes have their own environments, which are copies
of their parents. A Batch file is different in that it shares its
parents environment. So one thing you can do with a shell is to
set or modify an environmental variable using the SET command and
have it retained in the parent's environment.

Trouble is, a SHELL is also a child process, and I suspect that the
plain vanilla version also has its own environment copy, so the
parent's environment may go unmodified. Others have come up with
methods of doing a SHELL where the parent's environment is changed,
so you might need to look into that.

But really, you have other options. For instance, in the BAT file
you may perform IF ERRORLEVEL 1 ECHO OOPS! Got an Error #1. Since
you probably performed an @ECHO OFF at the top of the BAT file,
if the words "OOPS! Got an Error #1" pops up on the screen, you
just heard from your BAT file.

Of course you could also do it this way: IF ERRORLEVEL 1 ECHO
OOPS! Got an Error #1 > errflag.txt, then when the BAT file is
done. you can check for the existence of errflag.txt or even
open it and read the error that occurred. If you want your BAT
file to tell you more, just replace the > with two .'s (>> ),
which tells the system to just add more text to the contents of
errflag.txt.

I've noted with Windows 2000 Pro, that I can't seem to use the
single > and get anything written to the file, so I always have
to use the >>.

The statement that you can do anything in you program that a BAT
file can do is true, but not always easily. A one-liner like any
of these is a bit harder to do in your main program:

FOR %a IN (*.BAS) DO TYPE %a >> \project\bigfile.bas

FOR %a IN (*.BAS) DO ECHO $INCLUDE "%a" >> \project\include.inc

FOR %a IN (*.lst) DO TYPE %a | SORT >> %a.new

Or this simple BAT file:

@ECHO OFF
IF NOT EXIST %1.bat GOTO exit
IF EXIST %1.bk9 DEL %1.bk9
IF EXIST %1.bk8 REN %1.bk9
IF EXIST %1.bk7 REN %1.bk8
IF EXIST %1.bk6 REN %1.bk7
IF EXIST %1.bk5 REN %1.bk6
IF EXIST %1.bk4 REN %1.bk5
IF EXIST %1.bk3 REN %1.bk4
IF EXIST %1.bk2 REN %1.bk3
IF EXIST %1.bk1 REN %1.bk2
IF EXIST %1.bak REN %1.bk1
COPY %1.bas %1.bak
:exit

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Old Navy Chief, Systems Engineer, Systems Analyst, now semi-retired

[Frank Cox]

> But in a larger sense, why SHELL/Execute a batch file from
> an MS-DOS program at all?

You can actually run a bash script (Unix commandline) from PB/DOS using the UNIX command under DOSEMU.

It's a pretty slick trick for accomplishing stuff that you absolutely can't do directly from PB on Linux otherwise.

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[Michael Mattias]

But in a larger sense, why SHELL/Execute a batch file from an MS-DOS program at all?

Nothing you can do in a batch file you can't do with 'native' PB/DOS code anyway.

[Thomas Gohel]

On 10 Feb 05, Michael Mattias wrote:

Hello Michael,

> Don't know if this works when Program$ is a batch file, but it's
> worth a shot.

Not really Michael.

That's my own and very old source to this problem:
http://www.pbhq.de/cgi-bin/pbsearch....on=pbshell.bas

Regards,

--------------
/ h o m a s
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[Frank Cox]

> Don't know if this works when Program$ is a batch file,
> but it's worth a shot.

Not having actually tried it, I suspect that it wouldn't work because the return value you would get would be from command.com, and not from the program that command.com had run. One too many layers between you and the external program, as it were.



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[Michael Mattias]

' EXECDOS.BAS
' Execute an exteernal program as a child proccess, interrogate
' it's return code.
' For PB/DOS 3.2
' Author: Michael Mattias Racine WI 
' from original version for Microsoft QuickBASIC by Ethan Winer.


'============================================================
'     SUB TO Execute a program as a child process           
' Function value = return code of process; if < 0, error is 
' -1 * (dos error)
'============================================================

' REG equates as expected in REGS.INC
DEFINT A-Z
FUNCTION DosExecute% (Program$, Parameter$) LOCAL
  '---- Prepare the program name and parameter strings for processing.  DOS
  '     requires that the parameter string hold the length of the parameter
  '     text, followed by the parameter text, and then followed by a CHR$(13)
  '     Enter byte.  The parameter block holds two CHR$(0) bytes followed by
  '     the address and segment of the parameter string.
  '
  DIM Block   AS LOCAL STRING * 14    'this is the DOS parameter block
  DIM Parm    AS LOCAL STRING * 80    'and this is the actual parameter text

  DIM ZBuffer AS LOCAL STRING * 80    'this holds a copy of the program name

  SaveDefSeg = pbvDefSeg
  DEF SEG
  DefaultDS = pbvDefSeg
  Zero$ = CHR$(0)                  'invoke CHR$() only once for efficiency
  DOS = &H21                       'saves a few bytes
  ZBuffer$ = Program$ + Zero$      'make an ASCIIZ string for DOS

  LSET Parm$ = CHR$(LEN(Parameter$)) + Parameter$ + CHR$(13)
  LSET Block$ = Zero$ + Zero$ + MKI$(VARPTR(Parm$)) + MKI$(VARSEG(Parm$))

  Dummy& = SETMEM(-500000)         'free up memory for the program being run
  REG %RegAX, &h4B00
  REG %RegDX, VARPTR (ZBuffer$)
  REG %RegES, VARSEG(Block$)
  REG %RegBX, VARPTR(Block$) 
  REG %RegDS, DefaultDS
  CALL INTERRUPT DOS
  Flags = REG(0)
  ReturnAX = REG(%RegAX)
  IF (Flags AND 1) THEN          'DOS error trying to run the program?
    DosExecute% = -(ReturnAX)    'yes, set function value to -1 * error code
    GOTO Execute.Done            'and jump to reclaim memory
  END IF

  REG %RegAX, &H4D00               'retrieve subordinate process code
  CALL Interrupt DOS
  DosExecute% = REG (%RegAX)          'set function value to exit code

Execute.Done:
  Dummy& = SETMEM(500000)          'reclaim the memory relinquished eariler
  DEF SEG = SaveDefSeg             ' restore DS to what it was at entry.

END FUNCTION

Don't know if this works when Program$ is a batch file, but it's worth a shot.

If that doesn't work, you could run this from within your program once for each external program in the batch file, interrogating the return code each time.

MCM


[This message has been edited by Michael Mattias (edited February 10, 2005).]

[Frank Cox]

A simple work-around would be to make your batch file write a filename to the current directory using either echo or touch based on the errorlevel, then check which file exists when you re-enter your PB program.

In your batch file:

if errorlevel 2 echo.> level2.tmp

Then, in your PB program:

if len(dir$("level2.tmp"))>0 then
kill "level2.tmp" ' so we don't find it again on the next run by mistake
print "We found errorlevel 2 and now we can sing."
end if

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[Robert E. Carneal]

I would to run an BATch file from Powerbasic, but for it to
do me any good, I somehow need to transfer the ERRORLEVEL
value back to the program.

That is not possible, or is it? If possible, what gets/traps
the ERRORLEVEL value so it can get transferred/read by the
program?

Thank you.

Robert

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