#! /bin/sh
# #############################################################################

       NAME_="lowspace"
       HTML_="monitor space on device"
    PURPOSE_="notify when space on a device is less then n Megabytes"
   SYNOPSIS_="$NAME_ [-hlx] -i <n> -d <device> -t <n>s|m|h|d"
   REQUIRES_="standard GNU commands, xmessage"
    VERSION_="1.5"
       DATE_="1999-08-10; last update: 2005-02-28"
     AUTHOR_="Dawid Michalczyk <dm@eonworks.com>"
        URL_="www.comp.eonworks.com"
   CATEGORY_="admin"
   PLATFORM_="Linux"
      SHELL_="bash"
 DISTRIBUTE_="yes"

# #############################################################################
# This program is distributed under the terms of the GNU General Public License

usage () {

echo >&2 "$NAME_ $VERSION_ - $PURPOSE_
Usage: $SYNOPSIS_
Requires: $REQUIRES_
Options:
    -i <n>, an integer referring to Mb
    -d <device>, full path to the device eg: /dev/hda1
    -t <n>s|m|h|d, n is an integer referring to time interval in
       seconds|minutes|hours|days which refers to the frequency of how
       often to check for low space on the device
    -x, use xmessage to display a windowed notification if running X
    -h, usage and options (this help)
    -l, see this script"
    exit 1
}

shopt -s extglob # enabling extended globbing

time_validateSleepArg() {

    case $1 in
        +([0-9])[smhd] ) return 0 ;;
        *) return 1 ;;
    esac
}

# args check
[ $# -eq 0 ] && { echo >&2 missing argument, type $NAME_ -h for help; exit 1; }

# var init
xmsg=

while getopts hlxd:i:t: options; do

    case $options in
        i) mb=$OPTARG ;;
        d) device=$OPTARG ;;
        x) xmsg=on ;;
        t) time=$OPTARG ;;
        h) usage ;;
        l) more $0; exit 1 ;;
       \?) echo invalid argument, type $NAME_ -h for help; exit 1 ;;

    esac

done
shift $(( $OPTIND - 1 ))

# check if required command is in $PATH variable
if [ $xmsg ]; then
    which xmessage &> /dev/null
    [[ $? != 0 ]] && { echo >&2 the required \"xmessage\" command is not in your PATH; exit 1; }
fi

# args check
[[ $device ]] || { echo >&2 the -d option and argument must be specified; exit 1; }
[[ $time ]] || { echo >&2 the -t option and argument must be specified; exit 1; }
[[ $mb == *[!0-9]* ]] && { echo >&2 the argument to option -i must be an integer; exit 1; }

# sleep arg check
time_validateSleepArg $time
[ $? = 0 ] || { echo >&2 invalid argument to option -t, type $NAME_ -h for help; exit 1; }

# main
while :;do

    free=$(df -m | grep $device | { read dev blocks used avail perc mounted ; echo $avail; })
    [ $free ] || { echo >&2 wrong device name, type $NAME_ -h for help; exit 1; }

    if (( $free < $mb ));then

        if [ $xmsg ];then # display windowed message if x is running; ring a bell

            ps -aux | grep -q xinit
            if [ $? = 0 ];then
                echo -en \\a
                xmessage -center Device $device is running low on space! Only ${free}Mb left.
                exit
            else
                echo -e \\a Device $device is running low on space! Only ${free}Mb left.
                exit
            fi

        else # write message to terminal and ring a bell

            echo -e \\a Device $device is running low on space! Only ${free}Mb left.
            exit

        fi

    fi

    sleep $time # how often to check devices

done