Handle cases where there are no btrfs volumes.

            awk '$1 == "btrfs" {print $2}' | \

            sort -u)

do

    # In case there are no btrfs volumes, the for loop will execute once with an

    # empty string for mp. Validate that indeed we're passed a mountpoint.

    [ -d "$mp" ] || continue

    status="$(btrfs scrub status "$mp" | awk '$1 == "Status:" {print $2}')"

    if [ "$status" = 'running' ]

    then