for f in `ls`
do
        OLD=$f
        NEW=$(echo $f | sed 's/.*\([0-9]\{3\}\).*\.\(.*\)/Ep \1.\2/1')
        echo -n "$OLD => $NEW (o/n) "
        read YES_NO
        [[ $YES_NO == "y" ]] && mv $OLD $NEW
done

Ep 813.mp4
Ep 400.avi
Ep 483.avi

 echo $f | sed 's/[^0-9]*\([0-9]\{3\}\).*\.\(.*\)/Ep \1.\2/1'

[Various-PC3Ep 178.mp4
Ep 496.avi
Ep 483.avi

open(LS, "ls -1 |");
foreach (<LS>)
{
        $old = $_;
        $new = s/(?![0-9]{3})*([0-9]{3}).*\.(.*)/Ep $1.$2/;
        print "$old => $new (o/n) ";
        chomp($yes_no = <STDIN>);
        next unless ( $yes_no == "y");
        system("mv $old $new");
} #foreach

Ep 418.mp4
 => 1 (o/n) <- waiting here for input

foreach(`ls`)

Ep 418.mp4
  => 1 (o/n) <- waiting here for input

foreach (system("ls -1"))

 Various-PC3]_Some_Name_178_HD_[e2813be1].mp4
[TTB]_Some_Name_-_496_Vost_SD_(720x400_XviD_MP3).avi
Goffytofansub_Some name 483_HD.avi
0 =>  (o/n) <- waiting here for input