Question

I want to run an image backup (using command line on windows) once a day. I want to keep one image for each of the last three days, so I have to rotate between 3 paths on each backup run, e.g.

c:\image0.ext // encode as 0, see text below
c:\image1.ext // encode as 1
c:\image2.ext // encode as 2

I though about writing 0, 1 or 2 in a text file, reading it’s value somehow, then do sth. like (number+1) mod 2, execute backup, write the new number to the text file. I would then link each number from 0 to 2 to a path using an if statement. Are there better/easier ways for that? Thanks for any hint!

Answer 1

Since imageX.ext is a file, I assume it is some compressed archive of your data analagous to a zip file. The modified date should get updated each time it is replaced with a new version, so you should not need a separate file to keep track of what is your most recent image. You can use DIR sorted by date to get the most recent image (last one listed).

@echo off
for /f "delims=" %%F in ('dir /b /od c:\image?.ext') do set lastImage=%%F
set /a nextImage=(%lastimage:~-5,1%+1)%%3
set nextImage="c:\image%nextImage%.ext"

This algorithm will break if someone creates another file that matches your file mask after your last image was taken.