in windows what would be the "normal" return code, 0 or 1?

0 for success, like unix.

then did echo %ERRORLEVEL% and the value returned was -1.

That's weird. Error codes are unsigned in Win32. IF ERRORLEVEL even relies on that.

@echo off
program.exe

if errorlevel 3 goto ERROR
if errorlevel 1 goto WARNING

rem 0 <= errorlevel < 1
echo Success
goto END

:WARNING
rem 1 <= errorlevel < 3
echo Warning
goto END

:ERROR
rem 3 <= errorlevel
echo Error

:END
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That's a very strange error message to return in the event of a negative return code.

No, the message is correct for a negative code being returned from the function that implements system. The problem is that the function is returning negative when the child was successfully launched.

In Win32, exit codes are unsigned 32 bit values. Perl treats it as a signed 32-bit value.

DWORD status;
...
GetExitCodeProcess(ProcessInformation.hProcess, &status);
ret = (int)status;
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The second line is a bug. Sufficiently high exit codes will be converted to negative. Negatives are used to signal a problem launching the process.