Windows batch file: choosing a file from a directory based on directory name

I don't do windows batch programming, nor do I need to go that far down the rabbit hole.

I have d开发者_Python百科irectory structures as such:

dir1000000/file.txt
dir2000000_1/file.txt
dir2000000_2/file.txt

I need to select the file.txt from the path with the lexicographically greatest value, i.e. dir2000000_2/file.txt. How do I go about doing this?

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Assuming the file is always file.txt and only the directory is variable...

FOR /F "delims=" %%a IN ('DIR /ad/b/on') DO SET mydir=%%a
SET myfile=%mydir%\file.txt