#!/bin/bash
md5d() {
    [ -d "$1" ] && {
	find "$1" -type f -exec md5 {} \; | sort
    } || {
	md5 "$1"
    }
}
tac() {
    tail -r
}
set -- $(printf "%s\n" "$@" | tac)
base="$1"

while [ "$2" != '' ]; do
    for p in "$base"/*; do
	b="$(basename "$p")"
	if [[ -e "$2/$b" ]]; then
	    diff -q <(cd "$base" && md5d "$b") <(cd "$2" && md5d "$b") > /dev/null && {
		echo "$base/$b" "$2/$b" matched
		(cd "$2" &&
		     rm -rf "$b" &&
		     ln -s ../"$base/$b" .
		)
	    } || {
		:; # echo "$base/$b" and "$2/$b" differ
	    }
	else
	    :; # echo "$2/$b" not found
	fi
    done
    shift
done