Shell Programming and Scripting

opt=`bdf |grep -i /opt | awk '{print $5}' | sed 's/.$//'`
if [ $opt -ge 90 ]
then
        echo "ALERT YOUR SPACE IS TOO LESS ...PLEASE SEND MAIL TO..."
        #You send mail here
else
        echo " SPACE IS UNDER TIGHT CONTROL ;) "
fi

space=`df -v | grep -i "/opt" | awk '{print $6}'`

while :;do
       df -k | while read Filesystem kbytes used avail capacity Mounted; do
          case "$capacity" in
            *[0-9]%) [ "${capacity%\%}" -gt 90 ] && printf "%s:%15s%5s" \
		"$(hostname)" "$Mounted" "$capacity" | mailx -s "$(hostname): \
		Disk space alert"  your@address ;;
          esac
      done
  sleep 300
done