btrfs send all snapshots to other directory

btrfs_send_receive_snapshots.sh

#!/bin/bash

usage()
{
    echo "usage: `basename $0` from_directory to_directory"
}

if [ -z $1 ] || [ -z $2 ]; then
    usage
    exit 1
fi

# ROOT is the 1st argument, will search targets (udid)
FROM_ROOT=$1

# TO is the 2nd argument, will receive snapshot into
TO_ROOT=$2

# find all from target except snapshots
FROM_TARGETS=`find $FROM_ROOT -mindepth 1 -maxdepth 1 -type d | sort -n`

# there is an old backup dir has only snapshots
UNDER_SNAPSHOTS=0
rootbase=$(basename $FROM_ROOT)
if [ $rootbase = "snapshots" ]; then
    UNDER_SNAPSHOTS=1
fi

for f in $FROM_TARGETS
do 
    # B is target UDID extracted from FROM path
    TARGET_UDID=$(basename $f)

    # filter out `snapshots`
    if [ $TARGET_UDID != "snapshots" ]; then

        # construct path to target's snapshots
        FROM_UDID_ROOT="$FROM_ROOT/snapshots/$TARGET_UDID"

        # check whether ROOT is snapshots
        if [ $UNDER_SNAPSHOTS -eq 1 ]; then
            FROM_UDID_ROOT="$FROM_ROOT/$TARGET_UDID"
        fi

        # construct path for receiving
        TO_UDID_ROOT=$TO_ROOT/$TARGET_UDID

        echo "mkdir -p $TO_UDID_ROOT"
        mkdir -p $TO_UDID_ROOT

        echo "Starting sending in $TARGET_UDID ..."

        RET=0

        # # LAST is used to keep previous/parent snapshot path
        # LAST_UDID_TARGET=`find $TO_UDID_ROOT -mindepth 1 -maxdepth 1 -type d | sort -n | tail -n 1`
        # echo "LAST: $LAST_UDID_TARGET"
        # continue

        LAST_UDID_TARGET=""

        # find all snapshots under target's snapshots
        FROM_UDID_TARGETS=`find $FROM_UDID_ROOT -mindepth 1 -maxdepth 1 -type d | sort -n`
        for FROM_UDID_TARGET in $FROM_UDID_TARGETS
        do 
            RET=0
            TO_DATE=$(basename $FROM_UDID_TARGET)
            if [ ! -d $TO_UDID_ROOT/$TO_DATE ]; then
                if [ -z "$LAST_UDID_TARGET" ]; then
                    # didn't find a way to execute command with pipe inside a variable
                    CMD="btrfs send $FROM_UDID_TARGET | btrfs receive $TO_UDID_ROOT"
                    btrfs send $FROM_UDID_TARGET | btrfs receive $TO_UDID_ROOT
                    RET=$?
                else
                    # use -p argument when there is already a snapshot copy
                    CMD="btrfs send -p $LAST_UDID_TARGET $FROM_UDID_TARGET | btrfs receive $TO_UDID_ROOT"
                    btrfs send -p $LAST_UDID_TARGET $FROM_UDID_TARGET | btrfs receive $TO_UDID_ROOT
                    RET=$?
                fi
                LAST_UDID_TARGET=$FROM_UDID_TARGET
                if [ $RET -ne 0 ]; then
                    echo "failed to execute command: $CMD"
                    exit 1
                fi
           else
               echo "existed: $TO_UDID_ROOT/$TO_DATE"
           fi
        done
    fi
done