Jenkins - sometimes (non-deteministic?) mark builds as failed, because of batch command - batch-file

Question

I execute following batch ('Execute Windows batch command') through Jenkins. Although it always (tested more than 50 times) works when I build my project 'manually' (when I click on 'build' button), it sometimes crashes during scheduled builds.
REM
REM get date in following format - day name - day - month name - year
REM
for /f "delims=" %%a in ('wmic OS Get localdatetime ^| find "."') do (set dt=%%a)
set year=%dt:~0,4%
set month=%dt:~4,2%
set day=%dt:~6,2%
if %month%==01 set month=Jan
if %month%==02 set month=Feb
if %month%==03 set month=Mar
if %month%==04 set month=Apr
if %month%==05 set month=May
if %month%==06 set month=Jun
if %month%==07 set month=Jul
if %month%==08 set month=Aug
if %month%==09 set month=Sep
if %month%==10 set month=Oct
if %month%==11 set month=Nov
if %month%==12 set month=Dec
For /f %%# In ('WMIC Path Win32_LocalTime Get DayOfWeek^|Findstr [1-7]') Do (Set DOW=%%#)
if %dow%==1 set dow=Monday
if %dow%==2 set dow=Tuesday
if %dow%==3 set dow=Wednesday
if %dow%==4 set dow=Thursday
if %dow%==5 set dow=Friday
if %dow%==6 set dow=Saturday
if %dow%==7 set dow=Sunday
set dayinfo=%dow% - %day%-%month%-%year%
The error message is as follows:
For> /F
%# In ('WMIC Path Win32_LocalTime Get DayOfWeek|Findstr [1-7]') Do
(Set DOW=%# ) set was unexpected at this time.
if> ==1
set dow=Monday Build step 'Execute Windows batch command' marked build
as failure
Since I am unable to reproduce it - is it possible to make batch command not mark build as failed?
Is it a bug in Jenkins or within my batch file?

Answer 1

is it possible to make batch command not mark build as failed?
Yes, write echo Done or something as the last line in your Execute Windows Batch Command step (not in the batch itself). Since that line will always succeed, the whole step will be marked as successful always. Obviously, you are foregoing any possibility of the script failing for valid reasons though.
Now, the reason your script is failing is because in some circumstances (undetermined), your value for DOW is not set. So the comparison statement becomes invalid as it has no left side.
To avoid this, you should always quote your variables and strings in comparison.
if "%dow%"=="1" set dow=Monday
if "%dow%"=="2" set dow=Tuesday
This way, at least the script won't fail due to syntax errors, however you will still end up with empty dow (and incomplete dayinfo)
To figure out why exactly your dow ends up being empty sometimes, you need to actually see the result of the command that generates it's value. So do the following:
WMIC Path Win32_LocalTime Get DayOfWeek
For /f %%# In ('WMIC Path Win32_LocalTime Get DayOfWeek^|Findstr [1-7]') Do (Set DOW=%%#)
When it's successful, it will display the full output of the command in console. When it fails, you will see the error of that command, and take it from there.