A handy Bash script to monitor your internet connection, log downtimes, and notify you of changes in connectivity status.

Internet-Connectivity-Checker.sh

#!/bin/bash

# Default Configurations
DEFAULT_PING_HOSTS=("8.8.8.8" "1.1.1.1")
DEFAULT_CHECK_INTERVAL=10
DEFAULT_LOG_FILE="$(dirname "$0")/internet_downtime.log"

# Initialize Configurations
PING_HOSTS=("${DEFAULT_PING_HOSTS[@]}")
CHECK_INTERVAL=$DEFAULT_CHECK_INTERVAL
LOG_FILE=$DEFAULT_LOG_FILE

# Parse Command Line Arguments
while getopts "h:i:l:" opt; do
  case $opt in
    h) IFS=',' read -r -a PING_HOSTS <<< "$OPTARG";;
    i) CHECK_INTERVAL="$OPTARG";;
    l) LOG_FILE="$OPTARG";;
    *) echo "Usage: $0 [-h hosts] [-i interval] [-l logfile]"; exit 1;;
  esac
done

# Function Definitions
check_internet() {
    for host in "${PING_HOSTS[@]}"; do
        if /sbin/ping -c 1 "$host" &>/dev/null; then
            return 0
        fi
    done
    return 1
}

log_message() {
    echo "$(date) - $1" | tee -a "$LOG_FILE"
}

send_notification() {
    local message=$1
    if [ "$(uname)" == "Darwin" ]; then
        /usr/bin/osascript -e "Display notification \"$message\" with title \"Connectivity Alert\""
    elif [ "$(expr substr $(uname -s) 1 5)" == "Linux" ]; then
        notify-send "Connectivity Alert" "$message"
    fi
}

handle_exit() {
    log_message "Internet connectivity checker stopped."
    exit 0
}

# Trap SIGINT for graceful termination
trap handle_exit SIGINT

# Main Loop
log_message "Internet connectivity checker started."
notification_sent=0
down_times=0
longest_duration=0
downtime_start=0

while true; do
    if check_internet; then
        if [ "$notification_sent" -eq 1 ]; then
            send_notification "Internet is reconnected"
            notification_sent=0
            downtime_end=$(date +%s)
            duration=$((downtime_end - downtime_start))
            down_times=$((down_times + 1))
            longest_duration=$(($duration > $longest_duration ? $duration : $longest_duration))
        fi
        echo -ne "\rDowntimes: $down_times | Longest Duration: ${longest_duration}s | Status: \033[32mONLINE\033[0m"
    else
        if [ "$notification_sent" -eq 0 ]; then
            send_notification "Internet is disconnected"
            notification_sent=1
            downtime_start=$(date +%s)
            log_message "Internet down"
        fi
        echo -ne "\rDowntimes: $down_times | Longest Duration: ${longest_duration}s | Status: \033[31mOFFLINE\033[0m"
    fi
    sleep "$CHECK_INTERVAL"
done

Unfortunately the for loop doing pings only ever uses the first host.

This will be the last note. This script gives the appearance of working by happy accident. Function return values are not evaluated properly. You don't test the function by name after a call, you test $?. The value of the function name as a right hand side is itself (the spelling of the function).