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Q41533: BASIC 7.00 Can Return Exit Code (Error Level) to Batch File

Article: Q41533
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom B_GWBasicI SR# S890216-141 | mspl13_basic
Last Modified: 4-SEP-1990

MS-DOS batch processing (.BAT) files can use an "IF ERRORLEVEL n"
statement to detect exit code levels returned by some programs.

However, the only versions of Microsoft BASIC that allow a program to
return an error level code to MS-DOS are Microsoft BASIC Professional
Development System (PDS) versions 7.00 and 7.10. The END n or STOP n
statement returns error level n to the batch file that invoked the
BASIC 7.00 or 7.10 .EXE program. The IF ERRORLEVEL n statement in the
batch file can detect if the returned exit code is equal to or greater
than n.

In all other versions of Microsoft BASIC, the error level (exit) code
returned by a BASIC program is controlled by the BASIC run-time
module, not by your program. As an alternative, you can create a file
in the BASIC program to serve as a flag when a certain condition
occurs. The batch file that called your program can then check for the
existence of the flag file in place of checking for an error level. In
batch files, the "IF EXIST filename" command can be used.

The following products do not allow your program to return an error
level to MS-DOS batch files:

1. QuickBASIC versions 1.00, 1.01, 1.02, 2.00, 2.01, 3.00, 4.00,
   4.00b, and 4.50 for MS-DOS

2. Microsoft GW-BASIC versions 3.20, 3.22, and 3.23 for MS-DOS

3. Microsoft BASIC Compiler versions 5.35 and 5.36 for MS-DOS and
   versions 6.00 and 6.00b for MS-DOS and MS OS/2

Your BASIC program must not attempt to invoke any MS-DOS interrupts
(CALL INTERRUPT) to terminate the program with an error level;
otherwise, strange results may occur and the machine may hang. BASIC
must handle program termination by itself.

BASIC 7.00 or 7.10 Can Return Exit Code (ERRORLEVEL) to Batch File
------------------------------------------------------------------

An .EXE program compiled in BASIC 7.00 or 7.10 can use the STOP n% or
END n% statement to return an exit code (n%) to MS-DOS, as follows:

   ' TEST.BAS
   PRINT "This is a BASIC program that returns an exit code of 5."
   n% = 5
   END n%

The exit code can be trapped in a MS-DOS batch file with the IF
ERRORLEVEL n GOTO statement, as follows:

   TEST
   ECHO OFF
   IF NOT ERRORLEVEL 1 GOTO DONE
      ECHO  An error occurred with exit code 1 or higher.
   :DONE
   ECHO End of batch file.

Using a File as a Flag for a Batch File
---------------------------------------

The following technique lets any BASIC version give a simple yes or no
message to a batch file.

The following batch file, ERRT.BAT, calls the BASIC program ERRTST,
which drops back to the batch file. It then checks for the existence
of the file ERRFIL (which is an arbitrary name) to see if an error
occurred while running the BASIC program:

   echo off
   del errfil
   errtst
   if not exist errfil goto end
   echo An error occurred during program running
   :end
   echo End of batch file

The following file is ERRTST.BAS; it creates the error file if it
cannot open the file GARBAGE.DAT:

' set up to error out if "GARBAGE.DAT" does not exist
ON ERROR GOTO errorlevel
OPEN "garbage.dat" FOR INPUT AS #1
CLOSE #1
END
errorlevel:
   CLOSE #1
   OPEN "errfil" FOR OUTPUT AS #1   'Create file that acts as a flag
   CLOSE #1
   SYSTEM   ' Returns to DOS.

To demonstrate this procedure, compile and link ERRTST.BAS as follows:

   BC ERRTST.BAS;
   LINK ERRTST.OBJ;

Now run the batch file ERRT.BAT. If the BASIC program cannot find
GARBAGE.DAT, ERRT.BAT shows "An error occurred during program
running."

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