#!/bin/sh
for fn; do
  fn=$(echo "$fn" | sed "s/\/$//")
  n=$(($(ls -d "$fn".bak[0-9]* 2> /dev/null | egrep "\.bak[0-9]+$" | egrep -o "[0-9]+$" | sort -g | tail -n 1) + 1))
  cp -a "$fn" "$fn.bak$n"
done