gistfile1.txt

#!/usr/bin/env bash
PATH=/bin:/usr/bin
#
# (C)Copyright 2025 Henri Shustak
#
# Licence : GNU GPLv3 or later 
# https://www.gnu.org/licenses/gpl-3.0.html
#
#
# About : Check if a specific port is up or down on a specific host
#
#         This script will send an email on port state changes.
#         Port is now up (but was down) or is now down (but was up) will trigger such an email.
#
#         It is easy to modify this script so that rather than sending a message via mailx
#         some other action, script or notification takes place. Modify to make it work for you.
# 
# Known issues : 
#         The script uptime reporting is jankey only calculates human readable output up to days.
#         That could be improved greatly.
#
# Version History :
#
#   version 1.0 - initial release
#


##
## Variables
##


# allow varable setting via export - set to false if you want to diable enviroment varable overides
export_varable_overide_allowed="false"
evoa=$export_varable_overide_allowed

# able to overwritten via export - base variables
if [[ -z $host_to_check ]] || [[ "$evoa" == "false" ]] ; then host_to_check=localhost ; fi
if [[ -z $local_port_to_check ]] || [[ "$evoa" == "false" ]] ; then local_port_to_check=8787 ; fi
if [[ -z $interval_check_seconds ]] || [[ "$evoa" == "false" ]] ; then interval_check_seconds=5 ; fi

# base varables
state_change_file_up="/tmp/port-$host_to_check:$local_port_to_check-$BASHPID-state.up"
state_change_file_down="/tmp/port-$host_to_check:$local_port_to_check-$BASHPID-state.down"
host=$(hostname)
nc_status_current="0" # port up
nc_status_previous="unset" # port not set
port_status_email_string=""
last_state_change_epoch=0
current_epoch=$(date +%s)
last_state_change_epoch=$current_epoch
monitor_script_start_epoch=$current_epoch
debug_status="true" # disable for less output

# email varables
if [[ -z $recipient ]] || [[ "$evoa" == "false" ]] ; then recipient="[email protected]" ; fi
if [[ -z $sender ]] || [[ "$evoa" == "false" ]] ; then sender="[email protected]" ;fi



##
## Functions
##


function clean_exit() {
    rm -f $state_change_file_down
    rm -f $state_change_file_up
}

function state_changed_up() {
    rm -f $state_change_file_down
    touch $state_change_file_up
    if [[ "$debug_status" == "true" ]] ; then
        echo "state changed : up"
    fi
}

function state_changed_down() {
    rm -f $state_change_file_up
    touch $state_change_file_down
    if [[ "$debug_status" == "true" ]] ; then
        echo "state changed : down"
    fi
}

function state_change_detected() {

    # update the system uptime
    uptime=$(uptime -p)

    # setup the wording for the email
    if [[ $nc_status_current == 0 ]] ; then 
        port_status_email_string="has"
    else
        port_status_email_string="lost"
    fi

    # calculate time since last state change
    current_epoch=$(date +%s)
    elapsed_seconds=$(( $current_epoch - $last_state_change_epoch ))
    convert_seconds_to_human_readable_time
    time_since_last_state_change=$human_readable_time

    # calculate time since script started
    elapsed_seconds=$(( $current_epoch - $monitor_script_start_epoch ))
    convert_seconds_to_human_readable_time
    monitor_script_uptime=$human_readable_time

    # the position of this is important - in order to have the correct wording set 
    subject="$host $port_status_email_string connectivitiy to $host_to_check:$local_port_to_check"

    # setup the wording for the email
    if [[ $nc_status_current == 0 ]] ; then 
        port_status_email_string="up"
        state_changed_up
    else
        port_status_email_string="down"
        state_changed_down
    fi

    # send a custom email
    mailx -s "$subject" -a "From:$host <$sender>" -r "$sender" "$recipient" \
<<EOF
sent from $host 
      host uptime  :  $uptime 
    script uptime  :  $monitor_script_uptime


monitored port state change report :

         host  :  $host_to_check
         port  :  $local_port_to_check 
       status  :  $port_status_email_string
         time  :  ${time_since_last_state_change} (since last state change)

EOF

    # update the previous status variables
    nc_status_previous=$nc_status_current
    last_state_change_epoch=$current_epoch

    # report what happened with the eamil
    return $?
}

function convert_seconds_to_human_readable_time () {
    # make the human_readable_time variable have human readable formatting (days hours and miniutes or just seconds)
    elapsed_miniutes="$(( elapsed_seconds / 60 ))"
    elapsed_hours="$(( elapsed_miniutes / 60 ))"
    elapsed_days="$(( elapsed_hours / 24 ))"
    human_readable_time=""
    if [[ ${elapsed_hours} -ge 1 ]] ; then
        elapsed_miniutes="$(( elapsed_miniutes % 60 ))"
        if [[ ${elapsed_days} -ge 1 ]] ; then
            day_or_days="day" ; if [[ ${elapsed_days} -ge 2 ]] ; then day_or_days="days" ; fi
            elapsed_hours="$(( elapsed_hours % 24 ))"
            human_readable_time="${elapsed_days} ${day_or_days} "
        fi
        hour_or_hours="hour" ; if [[ ${elapsed_hours} -ge 2 ]] ; then hour_or_hours="hours" ; fi
        human_readable_time="${human_readable_time}${elapsed_hours} ${hour_or_hours} "
    fi
    miniute_or_miniutes="miniute" ; if [[ ${elapsed_miniutes} -ge 2 ]] ; then miniute_or_miniutes="miniutes" ; fi
    human_readable_time="${human_readable_time}${elapsed_miniutes} ${miniute_or_miniutes}"
    if [[ ${elapsed_miniutes} == 0 ]] ; then
        human_readable_time="${elapsed_seconds} seconds"
    fi
}



## 
## Logic
##


# set a trap to tidy up files
trap 'clean_exit' EXIT


# start the loop
while true ; do

    nc -z $host_to_check $local_port_to_check 2> /dev/null
    nc_status_current=$?

    if [[ "$nc_status_previous" != "$nc_status_current" ]] ; then
        # state change has occoured
        state_change_detected
    fi
    
    # pause the loop
    sleep $interval_check_seconds

done