BASH function to split ROS bags

bagcut.sh

# Use rosbag filter to create a new bag
#
# $ bagcut original.bag 0 336 # cuts from 0 to 336s
#
# $ bagcut original.bag 50 # new bag starts 50s in
#
# $ bagcut original.bag 10 -20 # cuts from 10 to END_TIME-20s
function bagcut {
        BAG=${1:0:-4}
        OFFSET=$2
        START=`rosbag info ${BAG}.bag | grep start | head -1 | tr -s ' ' | cut -d " " -f 6 | bc`
        END=`rosbag info ${BAG}.bag   | grep end   | head -1 | tr -s ' ' | cut -d " " -f 6 | bc`
        NEWSTART=`echo "$START + $OFFSET" | bc`

        # Is there an ending limit?
        if [ ! -z "$3" ]
        then
                if [ `echo "$3 < 0" | bc` -ne "0" ]
                then
                        END=`echo "$END - $3" | bc`
                else
                        END=`echo "$START + $3" | bc`
                fi
        fi

        rosbag info ${BAG}.bag | grep start | head -1
        rosbag info ${BAG}.bag | grep end   | head -1

        set -x
        rosbag filter ${BAG}.bag ${BAG}.split.bag "t.secs >= $NEWSTART and t.secs <= $END"
        { set +x; } 2>/dev/null
}