Calling several .exe-files in parallel from a Windows bat-file and piping the results to a common file?

Question

I would like to have a standard Windows .bat-file calling 3 instances of an .exe-file in parallel and pipe the result to a common text-file. Pseudo-code:

SET PATH_TO_OUTPUT_FILE=%~dp0"All Devices Contents.txt"

echo Device on COM1 returned the following: >  %PATH_TO_OUTPUT_FILE%
start /b  ReadFromComPortDevice.exe  COM1   >> %PATH_TO_OUTPUT_FILE%
echo Device on COM2 returned the following: >> %PATH_TO_OUTPUT_FILE%
start /b  ReadFromComPortDevice.exe  COM2   >> %PATH_TO_OUTPUT_FILE%
echo Device on COM3 returned the following: >> %PATH_TO_OUTPUT_FILE%
start /b  ReadFromComPortDevice.exe  COM3   >> %PATH_TO_OUTPUT_FILE%

Obviously, the above will create file access errors because the file will already be used by the first process. Does anybody know a workaround?

Answer 1

the simplest approach would to be to redirect the output of the batch file as a whole to the specified file:

@Echo off & CD /D "%~dp0"

If not defined _ (
 Set _=_
 Prompt $_
 Start /B "" "%~f0" >"All Devices Contents.txt"
 (Prompt )
 Exit /B
)

echo Device on COM1 returned the following:
start /b  ReadFromComPortDevice.exe  COM1
echo Device on COM2 returned the following:
start /b  ReadFromComPortDevice.exe  COM2
echo Device on COM3 returned the following:
start /b  ReadFromComPortDevice.exe  COM3

Set "_="
Goto :Eof