@echo off
REM logFile
set "logFile=%~dp0logDT.txt"
REM write
echo.%date:~0,10%,%time:~0,8%>>"%logFile%"
REM max line
set "maxLine=20"
REM current line num
for /f "tokens=3 delims=:" %%i in ('find /n /c "," "%~dp0\logDT.txt"') do set "curLine=%%i"
REM compare
set /a "key=%curLine%-%maxLine%"
if %key% gtr 0 ( 
	more +%key% "%logFile%" >"%~dp0tmp.txt"
	move /y "%~dp0tmp.txt" "%logFile%" >nul 2>nul
) 
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