How can I batch rename files using the Terminal?

Question

I have a set of files, all of them nnn.MP4.mov. How could I rename them so that it is just nnn.mov?

Answer 1

for i in *; 
do j=`echo $i | cut -d . -f 1`; 
j=$j".mov";
mv $i $j; 
done

this will cut everything before the first dot and appends .mov

but if some files are e.g. hi.2.mov and hi.1.mov one will be overwritten, so use it carefully ^^