rm_md5sum.sh

#!/bin/bash

# This script removes duplicate files in the directory given as
# argument. The files with the oldest modification date will be
# considered to be the originals, when other files with the same MD5
# hash are found.

set -eo pipefail

usage () {
	printf '\n%s\n\n' "Usage: $(basename "$0") [dir]"
	exit
}

if [[ -z $1 || ! -d $1 ]]; then
	usage
fi

dn=$(readlink -f "$1")

mapfile -t files < <(find "$dn" -type f 2>&-)

declare -A md5s_date md5s_fn md5s_og

for (( i = 0; i < ${#files[@]}; i++ )); do
	fn="${files[${i}]}"

	md5_fn=$(md5sum -b <<<"$fn")
	md5_fn="${md5_fn%% *}"
	md5=$(md5sum -b "$fn")
	md5="${md5%% *}"
	date=$(stat -c '%Y' "$fn")

	if [[ -n ${md5s_date[${md5}]} ]]; then
		if [[ $date -lt ${md5s_date[${md5}]} ]]; then
			md5s_date["${md5}"]="$date"
			md5s_og["${md5}"]="$fn"
		fi
	else
		md5s_date["${md5}"]="$date"
		md5s_og["${md5}"]="$fn"
	fi

	md5s_fn["${md5_fn}"]="$md5"
done

for (( i = 0; i < ${#files[@]}; i++ )); do
	fn="${files[${i}]}"

	md5_fn=$(md5sum -b <<<"$fn")
	md5_fn="${md5_fn%% *}"
	md5="${md5s_fn[${md5_fn}]}"

	if [[ -n ${md5s_og[${md5}]} ]]; then
		if [[ $fn != "${md5s_og[${md5}]}" ]]; then
			printf '%s\n' "$fn"
			rm -f "$fn"
		fi
	fi
done