FreeNAS / camcontrol disk spindown check shell script with logging

spincheck.sh

#!/bin/sh
###########################################################################
# spincheck.sh
#
# Determines the power status of given disks without waking them through
# usage of smartctl.
#
# Author: Niels Gandrass
# Version: 1.0
# Since: 15.05.2017
###########################################################################

##### BEGIN Config parameters #####

# Determines where the output log is written to
spinlogfile="spincheck.log"
#spinlogfile="/dev/null"

# Command used to log output
log_output="tee -a $spinlogfile"

# Prefix used for device matching
device_prefix="ada"

# Time between checks in seconds
interval=600

#### END Config parameters #####



# Clear logfile
#echo "" > $spinlogfile

# Get devicelist
devices=`camcontrol devlist | grep ada | sed "s/.*(.*,\($device_prefix[0-9]*\))/\1/"`

# Print devicelist-header
printf "%20s" "" | $log_output
for device in $devices; do
    printf "%5s" $device | $log_output
done
printf "\n" | $log_output

# Main loop
while [ 1 ]; do

    printf "%20s" "`date +"%d.%m.%Y %H:%M:%S"`" | $log_output
    for device in $devices; do
        printf "%5s" "`camcontrol cmd $device -a "E5 00 00 00 00 00 00 00 00 00 00 00" -r - | cut -d " " -f 10 | sed "s/FF/1/" | sed "s/00/0/"`" | $log_output
    done
    printf "\n" | $log_output

sleep $interval
done