Prepending or appending a datetime stamp using Batch

append_datetime.bat

@echo off

rem set general variables
set input_files=*.txt

rem set date/time variables (generates yyyy-mm-dd_hhmmss)
for /f "tokens=2-4 delims=/ " %%a in ('date /t') do (set file_date=%%c-%%a-%%b)
for /f "tokens=1-3 delims=:." %%a in ("%TIME%") do (set file_time=%%a%%b%%c)
set date_time=%file_date%_%file_time%

rem appends _yyyy-mm-dd_hhmmss after file name (before extension) to all filed matched by input_files
for %%a in (%input_files%) do ren "%%~a" "%%~na_%date_time%%%~xa"

prepend_datetime.bat

@echo off

rem set general variables
set input_files=*.txt

rem set date/time variables (generates yyyy-mm-dd_hhmmss)
for /f "tokens=2-4 delims=/ " %%a in ('date /t') do (set file_date=%%c-%%a-%%b)
for /f "tokens=1-3 delims=:." %%a in ("%TIME%") do (set file_time=%%a%%b%%c)
set date_time=%file_date%_%file_time%

rem prepends yyyy-mm-dd_hhmmss_ before full file name (including extension) to all filed matched by input_files
for %%a in (%input_files%) do ren "%%~a" "%date_time%_%%~nxa"