Utility to monitor host availability changes by ping, with timestamps and durations

pingavail.sh

#!/bin/bash -l
# Utility to monitor host availability changes by ping, with timestamps and durations
HOST="$1"
ONLINE_INTERVAL=5
OFFLINE_INTERVAL=1
TIMEOUT=500

if [ "x$HOST" == "x" ]; then
    echo "usage: $(basename "$0") host"
    exit
fi

echo "Monitoring on $HOST. Probe interval: $ONLINE_INTERVAL/$OFFLINE_INTERVAL, Ping timeout: $TIMEOUT"

ping_ex () {
    local HOST=$1
    local TIMEOUT=$2
    local RETRIES=$3

    for ((i=0; i < RETRIES; i++)); do
        ping -W $TIMEOUT -c1 $HOST > /dev/null 2> /dev/null
        if [ $? -eq 0 ]; then
            return 0
        fi
    done

    return 1
}

STATE=-1
TIMESTAMP=0
while true
do
    NEXT_INTERVAL=0
    if [ $STATE -eq 1 ]; then
        NEXT_INTERVAL=$ONLINE_INTERVAL
        ping_ex "$HOST" "$TIMEOUT" 3
    else
        NEXT_INTERVAL=$OFFLINE_INTERVAL
        ping_ex "$HOST" "$TIMEOUT" 1
    fi
    RESULT=$(expr "$?" = "0")
    if [ $STATE -ne $RESULT ]; then
        STATE=$RESULT
        if [ $TIMESTAMP -ne 0 ]; then
            DT=$(($(date +%s)-TIMESTAMP))
            ELAPSED="$(date -ur $DT +%T)";ELAPSED=${ELAPSED#"00:"};
            echo "           ΔT $ELAPSED"
        fi
        TIMESTAMP=$(date +%s)
        TIME=$(date +"%T")
        if [ $STATE -eq 1 ]; then
            echo "$TIME – ONLINE"
        else
            echo "$TIME – OFFLINE"
        fi
    fi
    sleep $NEXT_INTERVAL
done