local/bin/btrfs-backup: Add script for easy btrfs incremental backups.

.local/bin/btrfs-backup

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+usage () {
+	cat <<EOF>&2
+Usage: ${0##*/} SOURCE TARGET
+
+Synchronize all the snapshots in the SOURCE/.snapshots to TARGET/.snapshots.
+
+EOF
+}
+
+if [ $# -ne 2 ]; then
+	usage
+	exit 1
+fi
+
+SOURCE="$1"
+TARGET="$2"
+
+for i in "$SOURCE"/.snapshots/*; do
+	if echo "$i" | grep -q 2019 ; then
+		echo "TODO: Temporarily ignoring snapshot '$i' with dates directly in .snapshots."
+		continue
+	fi
+	parent=""
+	target_i="$TARGET/.snapshots/$(basename "$i")"
+	for j in "$i"/*; do
+		if [ ! -e "$target_i/$(basename "$j")" ]; then
+			if [ -z "$parent" ] ; then
+				sudo btrfs send "$j" | sudo btrfs receive "$target_i"
+			else
+				sudo btrfs send -p "$parent" "$j" | sudo btrfs receive "$target_i"
+			fi
+		fi
+		parent="$j"
+	done
+	## Unset parent for next "i" subvolume.
+	parent=""
+done