Setting a windows batch file variable to the day of the week

Question

I have a windows batch file that runs daily. Wish to log data into a file and want to rotate it (i.e. having at most the last 7 days worth of data).

Looked into the

Answer 1

Another spin on this topic. The below script displays a few days around the current, with day-of-week prefix.

At the core is the standalone :dpack routine that encodes the date into a value whose modulo 7 reveals the day-of-week per ISO 8601 standards (Mon == 0). Also provided is :dunpk which is the inverse function:

@echo off& setlocal enabledelayedexpansion
rem 10/23/2018 daydate.bat: Most recent version at paulhoule.com/daydate
rem Example of date manipulation within a .BAT file.
rem This is accomplished by first packing the date into a single number.
rem This demo .bat displays dates surrounding the current date, prefixed
rem with the day-of-week.

set days=0Mon1Tue2Wed3Thu4Fri5Sat6Sun
call :dgetl y m d
call :dpack p %y% %m% %d%
for /l %%o in (-3,1,3) do (
  set /a od=p+%%o
  call :dunpk y m d !od!
  set /a dow=od%%7
  for %%d in (!dow!) do set day=!days:*%%d=!& set day=!day:~,3!
  echo !day! !y! !m! !d!
)
exit /b


rem gets local date returning year month day as separate variables
rem in: %1 %2 %3=var names for returned year month day
:dgetl
setlocal& set "z="
for /f "skip=1" %%a in ('wmic os get localdatetime') do set z=!z!%%a
set /a y=%z:~0,4%, m=1%z:~4,2% %%100, d=1%z:~6,2% %%100
endlocal& set /a %1=%y%, %2=%m%, %3=%d%& exit /b


rem packs date (y,m,d) into count of days since 1/1/1 (0..n)
rem in: %1=return var name, %2= y (1..n), %3=m (1..12), %4=d (1..31)
rem out: set %1= days since 1/1/1 (modulo 7 is weekday, Mon= 0)
:dpack
setlocal enabledelayedexpansion
set mtb=xxx  0 31 59 90120151181212243273304334& set /a r=%3*3
set /a t=%2-(12-%3)/10, r=365*(%2-1)+%4+!mtb:~%r%,3!+t/4-(t/100-t/400)-1
endlocal& set %1=%r%& exit /b


rem inverse of date packer
rem in: %1 %2 %3=var names for returned year month day
rem %4= packed date (large decimal number, eg 736989)
:dunpk
setlocal& set /a y=%4+366, y+=y/146097*3+(y%%146097-60)/36524
set /a y+=y/1461*3+(y%%1461-60)/365, d=y%%366+1, y/=366
set e=31 60 91 121 152 182 213 244 274 305 335
set m=1& for %%x in (%e%) do if %d% gtr %%x set /a m+=1, d=%d%-%%x
endlocal& set /a %1=%y%, %2=%m%, %3=%d%& exit /b