backup_folders.sh

#! /bin/bash

ECD=5
RECIPIENT=<REDACTED>
SRC=${1%/}
DST=${2%/}

# $1 folder to index
# $2 index file
function create_idx {
	touch "$2"
	exec 3<> "$2"
	cd "$1" || exit $ECD
	find . -type f -exec sha256sum "{}" \; >&3
	exec 3>&-
	cd - || exit $ECD
	sort -o "$2" "$2" 
}

echo "Backing up and encrypting directories in \"$SRC\" to \"$DST\""

mkdir -p "$DST/$(basename "$SRC")"
while IFS= read -r -d '' DIR
do
	IDX="$DST/$(basename "$(dirname "$DIR")")/.$(basename "$DIR").idx" 
	IDX2=$(mktemp -q)
	if [ ! -f "$IDX" ]; then
		echo "Creating index file: $IDX"
		create_idx "$DIR" "$IDX"
		tar -v -C "$SRC" -c "$(basename "$DIR")" | gpg --compress-level 0 \
		                                               --output "$DST/$(basename "$SRC")/$(basename "$DIR").tar.gpg" \
		                                               --encrypt --recipient "$RECIPIENT"
	else
		create_idx "$DIR" "$IDX2"
		if cmp -s "$IDX" "$IDX2"; then
			echo "No changes"
		else
			echo "Changes detected"
			diff "$IDX" "$IDX2"
			cp "$IDX2" "$IDX"
			tar -C "$SRC" -c "$(basename "$DIR")" | gpg --compress-level 0 --batch --yes \
			                                            --output "$DST/$(basename "$SRC")/$(basename "$DIR").tar.gpg" \
			                                            --encrypt --recipient "$RECIPIENT"
		fi
		rm "$IDX2"
	fi
done < <(find "$SRC" -maxdepth 1 -mindepth 1 -type d -not -iname '.*' -print0)