# FS usage limit in %
USAGE_LIMIT=80

IP="$(/sbin/ifconfig eth0 | grep 'inet addr:' | awk '{print $2}' | sed 's/[[:alpha:]:]*//')"

# multiple recepients may be specified separated by white space
MAILTO="root"
SUBJECT="WARNING: Disk usage on $IP over limit ($USAGE_LIMIT%)"
TMP_FILE="$(mktemp /tmp/XXXXXXXX)"

#
# Here we go
#

df -l | grep -v ^Filesystem | while read line; do
    fs=$(echo $line | awk '{print $6}')
    usage=$(echo $line | awk '{print $5}' | sed 's/%//')
    if [ $usage -gt $USAGE_LIMIT ]; then
        echo $fs : $usage% >> $TMP_FILE
    fi
done

# send warning in case there is something to send
[ -s "$TMP_FILE" ] && cat $TMP_FILE | mail -s "$SUBJECT" "$MAILTO"

rm -f "$TMP_FILE"