bash: detect SSD/HDD and set appropriate disk scheduler

set_disk_scheduler.sh

# set disk scheduler
sed -i "/^echo .*queue\/scheduler$/d" /etc/rc.local
for d in /dev/sd?
do
  device=${d/\/dev\//}
  rotational=$(cat /sys/block/${device}/queue/rotational)

  if   [ "$rotational" = "0" ] ; then
    echo noop > /sys/block/${device}/queue/scheduler
    echo "echo noop > /sys/block/${device}/queue/scheduler" >> /etc/rc.local
    echo "Set SSD $d scheduler to 'noop'."

  elif [ "$rotational" = "1" ] ; then
    echo deadline > /sys/block/${device}/queue/scheduler
    echo "echo deadline > /sys/block/${device}/queue/scheduler" >> /etc/rc.local
    echo "Set HDD $d scheduler to 'deadline'."

  else
    echo "Unknown device type (SSD/HDD) for $d: No changes made to scheduler."
  fi
done