If you need the number of week in a batch file you can use the following script.
I found it on internet on a in a Tech support forum
@echo off
set daysofweek=Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday
for /F "skip=2 tokens=2-4 delims=," %%A in ('WMIC Path Win32_LocalTime Get DayOfWeek /Format:csv') do set daynumber=%%A
echo MyFileBackup_%daynumber%.Bak
pause
for /F "tokens=%daynumber% delims=," %%B in ("%daysofweek%") do set day=%%B
echo MyFileBackup_%day%.Bak
pause
