Mac WiFI Monitor; A bash script that keeps checking if the WiFi connection alive on your Mac by continuously sending pings to the router and public DNSes. If the connection seemed lost nonetheless, the script automatically restarts the WiFi adapter.

mac-wifi-monitor.sh

#!/bin/bash

#  Mac WiFi Monitor
# ------------------ ---- -- -
#  Keeps checking if the WiFi connection alive
#  by continuously sending pings to the router and public DNSes.
#  If the connection seemed lost nonetheless,
#  automatically restarts the WiFi device on your Mac
# ====================================================
#   Author: amekusa.com
#  Version: 2.2.0
#  Updated: 2021-09-27

# ---- Settings --------
# Network device to monitor (leave it commented out to automatically detect the WiFi device)
# DEV=en1
# NOTE: To list all the devices:
# $ networksetup -listallhardwareports
PING_TO=(192.168.1.1  1.1.1.1  8.8.8.8  4.2.2.2)
PING_INTERVAL=3 # seconds
PING_TIMEOUT=1 # seconds
PING_SIZE=0 # bytes
AUDIBLE_ALERTS=true # true or false
PROMPT_RESTART=false # true or false
LOG_TO_FILE=true # true or false
LOG_FILE="$HOME/.wifi-monitor.log"
SYSLOG=false # true or false
# NOTE: syslog on High Sierra is broken
# ==== END Settings ====

trap _quit SIGINT
_quit() {
  echo
  _ts; _log "Finished by user input     @ $ts"
  exit
}

_ts() {
  ts=$(date +'%H:%M:%S %b %d, %Y')
}

_log() {
  [ "$log" = "$1" ] && return # don't repeat the same message
  $LOG_TO_FILE && echo "$1" >> $LOG_FILE
  $SYSLOG && syslog -s "[WiFi Monitor] $1"
  echo "$1"
  log="$1"
}

_active() {
  [[ $(networksetup -getairportpower $DEV) == *On ]]
}

_ping() {
  ping -c 1 -s $PING_SIZE -t $PING_TIMEOUT -n ${PING_TO[$1]} &> /dev/null
}

_restart() {
  _log "Restarting $DEV ..."
  networksetup -setairportpower $DEV off
  sleep 1
  networksetup -setairportpower $DEV on
  _state 1
}

_state() {
  _ts
  case $1 in
    0) _log "The device got deactivated @ $ts" ;;
    1) _log "The device got activated   @ $ts" ;;
    2) _log "Internet connection alive  @ $ts" ;;
  esac
  state=$1
}

_loop() {
  case $state in

  2) # online
    i=0
    _log "Started pinging to ${PING_TO[$i]} ..."
    while [ $i -le $iMax ]; do
      if _ping $i; then
        if [ $i -gt 0 ]; then
          _log "   Ping to ${PING_TO[$i]} succeeded"
          i=0
        fi
        sleep $PING_INTERVAL
      else # ping failed
        if ! _active; then
          _state 0; sleep 1
          return
        fi
        if [ $i -eq 0 ]; then
          _ts
        elif $AUDIBLE_ALERTS && [ $i -lt $iMax ]; then
          afplay -v .5 /System/Library/Sounds/Hero.aiff &
        fi
        _log "!) Ping to ${PING_TO[$i]} failed"
        ((i++))
      fi
    done
    _log "!) Connection lost         @ $ts"
    $AUDIBLE_ALERTS && afplay /System/Library/Sounds/Purr.aiff &
    if $PROMPT_RESTART; then
      while true; do
        read -n 1 -p "Restart WiFi device (Y/N) ? " answer
        echo
        case $answer in
          [Yy]) _restart; return ;;
          [Nn]) _ts; _log "Resumed monitoring $DEV     @ $ts"; return ;;
          *) echo "!) Type Y to restart, N to continue monitoring" ;;
        esac
      done
    fi
    _restart
    ;;

  1) # device active
    i=0
    while ! _ping $i; do
      _log "Waiting for internet connection ..."
      if ! _active; then
        _state 0; sleep 1
        return
      fi
      if [ $i -ge $iMax ]; then i=0; else ((i++)); fi
    done
    $AUDIBLE_ALERTS && afplay -v .5 /System/Library/Sounds/Submarine.aiff &
    _state 2; sleep $PING_INTERVAL
    ;;

  0) # device inactive
    while ! _active; do
      _log "Waiting for the device to be activated ..."
      sleep 1
    done
    _state 1
    ;;

  esac
}

# ---- Initialize --------

# clear the existing log file
$LOG_TO_FILE && [ -f $LOG_FILE ] && true > $LOG_FILE

# initialize variables
[ -z $DEV ] && DEV=$(networksetup -listallhardwareports | awk -F': ' '/Wi-Fi/{getline; print $2;}')
iMax=$((${#PING_TO[@]}-1)) # PING_TO.length - 1
if _active; then
  state=1
else
  state=0; sleep 1
fi

# ---- Main --------
_log "Monitoring the network device '$DEV' ..."
while _loop; do
  : # noop
done
_ts; _log "The script stopped due to an unknown error @ $ts"

This bash script continuously sends pings to public DNSes at 3-seconds intervals to keep internet connection alive.
If the connection was lost nonetheless for whatever reason, the script automatically restarts the WiFi device.