disk usage check

.bash

#!/bin/bash

email=overlord@localhost
free_threshold=20
next_reminder=$((60*60*24*3))
disks=(/dev/sda1 ...)

for disk in ${disks[*]}; do
  total=$(df $disk -P | tail -n 1 | awk '{print $2}')
  free=$(df $disk -P | tail -n 1 | awk '{print $4}')
  free_percentage=$((free*100/total))
  cache_file=~/.du-$(basename $disk)

  if [ $free_percentage -le $free_threshold ]; then
    last_notified=$(stat -c %Y $cache_file 2>/dev/null || echo 0)
    now=$(date +%s)
    time_elapsed=$((now-last_notified))

    if [ $time_elapsed -ge $next_reminder ]; then
      (
        echo    "There is low (less than $free_threshold%) free disk space left on"
        echo -n "the device $disk"
        if grep $disk /etc/mtab >>/dev/null 2>&1; then
          echo -n ", mounted at $(grep $disk /etc/mtab | awk '{print $2}')"
        fi
        echo     "."
        echo
        echo     "Kindest regards,"
        echo     "$(uname -s) at $(uname -n)"
      ) | mail -s "Alert - Device $(basename $disk) is low on disk space" $email &&

      touch $cache_file
    fi
  else
    rm -f $cache_file
  fi
done