While loop in batch

Question

Here is what I want, inside the BACKUPDIR, I want to execute cscript /nologo c:\deletefile.vbs %BACKUPDIR% until number of files inside the folder is greater than 21(countfiles holds it). Here is my code:

@echo off
SET BACKUPDIR=C:\test
for /f %%x in ('dir %BACKUPDIR% /b ^| find /v /c "::"') do set countfiles=%%x

for %countfiles% GTR 21 (
cscript /nologo c:\deletefile.vbs %BACKUPDIR%
set /a countfiles-=%countfiles%
)

Answer 1

set /a countfiles-=%countfiles%

This will set countfiles to 0. I think you want to decrease it by 1, so use this instead:

set /a countfiles-=1

I'm not sure if the for loop will work, better try something like this:

:loop
cscript /nologo c:\deletefile.vbs %BACKUPDIR%
set /a countfiles-=1
if %countfiles% GTR 21 goto loop