Recursively changes the names of all files and directories to lowercase (no support for symlinks)

tolower

#!/bin/sh

rename_twice() {
    local IFS
    local from="$1"
    local to="$2"

    [ "$from" = "$to" ] && return
    mv "$from" "${from}_"
    mv "${from}_" "$to"
}

rename_dirs() {
    local IFS lower dir

    find -maxdepth 1 -type d | while read dir; do
        [ "$dir" = "." ] && continue
        lower="$(echo "$dir" | tr '[A-Z]' '[a-z]')"
        rename_twice "$dir" "$lower"
        cd "$lower" 2>/dev/null || continue
        printf 'd'
        rename_dirs
        cd ..
    done
}

rename_files() {
    local IFS lower file

    find ! -type d | while read file; do
        lower="$(echo "$file" | tr '[A-Z]' '[a-z]')"
        rename_twice "$file" "$lower"
        printf 'f'
    done
}

rename_dirs
echo

rename_files
echo