Shorrty

Как-то так:

for SRC in `find . ! -type d`

do

    DST=`dirname "${SRC}"`/`basename "${SRC}" | tr '[A-Z]' '[a-z]'`

    if [ "${SRC}" != "${DST}" ]

    then

        [ ! -e "${DST}" ] && mv -T "${SRC}" "${DST}" || echo "${SRC} was not renamed"

    fi

done