|@guapo: right idea, just needs a boost:|
There are various ways, but maybe the easiest (and therefore, according to Occam, best) method is like this:
@echo off & setlocal enabledelayedexpansion
for /f "tokens=1,2 delims=!" %%a in ('dir /b *.flv') do (
echo ren "%%a^!"%%b %%a_%%b
other methods involve disabling delayedexpansion, but that gets messy, imo. This will of course fail (as written) if more than one "!" is in the filename-path.