hofi's rename script from http://hofbauer.bplaced.net/cms/2012/08/automatically-rename-files-and-folders/; adapted for style

rename2.sh

#!/bin/bash

DIR="$1"

# only start rename when $DIR is not root or empty
if [ "$DIR" == "" ] || [ "$DIR" == "/" ]; then
    echo "No directory given" >&2
    exit 1
fi

echo "Working on $DIR"

find "$DIR" -depth -print0 | xargs -0 -i rename 'y/A-ZÄÖÜ /a-zäöü_/;s/ä/ae/g;s/ö/oe/g;s/ü/ue/g;s/ß/ss/g;s/,//g' {}