First, make sure you are on the right directory on mac terminal app.
If you want to change only jpg files you can use $ for f in *.JPG;
instead of $ for f in *;
$ for f in *; do mv "$f" "`echo $f | tr "[:upper:]" "[:lower:]"`"; done
$ for f in *; do mv "$f" "`echo $f | tr " " "-"`"; done
Use \000
to remove characters
$ for f in *; do mv "$f" "`echo $f | tr "," "\000"`"; done