Date arithmetic in dos scripting

Question

I need to write a script to change a filename from aDate.txt to bDate.txt where:

• aDate is the current system date in yyyymmdd format and
• bDate is the current system date - 1 in yyyymmdd format.

I currently have:

set yy=%date:~6,2%
set mm=%date:~3,2%
set dd=%date:~0,2%
if "%date:~6,1%"==" " set yy=0%yy:~1,1%
if "%date:~3,1%"==" " set mm=0%mm:~1,1%
if "%date:~0,1%"==" " set dd=0%dd:~1,1%
SET sys_date=20%yy%%mm%%dd%
ECHO %sys_date%
REM still have to do this bit properly
SET sys_date_yesterday=%sys_date%a
move %sys_date%.txt %sys_date_yesterday%.txt

but I have no idea how to do the date -1 thing (other than the long winded) subtract 1 from the day and if that is = 0 then subtract one from the month and set the day = to the last day of the new month and so on for years.

Any ideas?

Answer 1

You have to do it the difficult way. I suggest to use this solution by SteveGTR. I copy the text below, because at least at least I cannot always see the solution on that site.

---

Here's a batch file I developed to subtract any number of days from the current date. It accepts a command line parameter of the number of days. The default is 1 day (yesterday):

@echo off

set yyyy=

set $tok=1-3
for /f "tokens=1 delims=.:/-, " %%u in ('date /t') do set $d1=%%u
if "%$d1:~0,1%" GTR "9" set $tok=2-4
for /f "tokens=%$tok% delims=.:/-, " %%u in ('date /t') do (
 for /f "skip=1 tokens=2-4 delims=/-,()." %%x in ('echo.^|date') do (
    set %%x=%%u
    set %%y=%%v
    set %%z=%%w
    set $d1=
    set $tok=))

if "%yyyy%"=="" set yyyy=%yy%
if /I %yyyy% LSS 100 set /A yyyy=2000 + 1%yyyy% - 100

set CurDate=%mm%/%dd%/%yyyy%

set dayCnt=%1

if "%dayCnt%"=="" set dayCnt=1

REM Substract your days here
set /A dd=1%dd% - 100 - %dayCnt%
set /A mm=1%mm% - 100

:CHKDAY

if /I %dd% GTR 0 goto DONE

set /A mm=%mm% - 1

if /I %mm% GTR 0 goto ADJUSTDAY

set /A mm=12
set /A yyyy=%yyyy% - 1

:ADJUSTDAY

if %mm%==1 goto SET31
if %mm%==2 goto LEAPCHK
if %mm%==3 goto SET31
if %mm%==4 goto SET30
if %mm%==5 goto SET31
if %mm%==6 goto SET30
if %mm%==7 goto SET31
if %mm%==8 goto SET31
if %mm%==9 goto SET30
if %mm%==10 goto SET31
if %mm%==11 goto SET30
REM ** Month 12 falls through

:SET31

set /A dd=31 + %dd%

goto CHKDAY

:SET30

set /A dd=30 + %dd%

goto CHKDAY

:LEAPCHK

set /A tt=%yyyy% %% 4

if not %tt%==0 goto SET28

set /A tt=%yyyy% %% 100

if not %tt%==0 goto SET29

set /A tt=%yyyy% %% 400

if %tt%==0 goto SET29

:SET28

set /A dd=28 + %dd%

goto CHKDAY

:SET29

set /A dd=29 + %dd%

goto CHKDAY

:DONE

if /I %mm% LSS 10 set mm=0%mm%
if /I %dd% LSS 10 set dd=0%dd%

echo Date %dayCnt% day(s) before %CurDate% is %mm%/%dd%/%yyyy%

Good Luck, Steve

Answer 2

This also works:

http://www.robvanderwoude.com/datetiment.php#Yesterday

It is very complete in that it checks the registry for local date format settings and uses those when creating the yesterday date.