lightsout for linux (suspend when no network activity for 1 hour)

linux_lightsout.bash

#!/bin/bash
########################################################################
# LIGHTS OUT FOR LINUX (lofl)                                          #
# This script suspends the computer if it's idle for a given period of #
# time. It monitors network activity, logged on users and CPU load.    #
########################################################################

# maximum packet count per minute – usually not more than 12-15
net_threshold=12

# maximum CPU load
load_threshold=0.4

# maximum IDLE time in minutes
time_threshold=60

# network interface to watch
interface=eno1


### DO NOT CHANGE ANYTHING BELOW THIS LINE #############################

# TODO: calculate $net_threshold if not set

# store user count and load in variables
system_up=$(uptime)
system_users=$(echo "$system_up" | perl -ne "print for /([0-9]+)\suser/")
system_load=$(echo "$system_up" | perl -ne "print for /([0-9]+\,[0-9]{2})$/" | sed "s/,/./")
# tell the user
printf "Logged in users:\t$system_users\n"
printf "Load avg (15min):\t$system_load (max $load_threshold)\n"

# create a temporary file to store the network packet count across calls
countfile="/tmp/lightsout_${interface}_count"
printf "Interface:\t\t$interface\n"
if [[ -f $countfile ]]
  then
    changed=$(date -r $countfile +%s)
    printf "Last record:\t\t$(date -d @"$changed")\n"
  else
    printf "0" > $countfile
fi

# see how many network packets were sent over the given interface
packet_sent=$(cat /sys/class/net/$interface/statistics/tx_packets)
# calculate the difference to the last call of the script
let "packet_difference=$packet_sent-$(cat $countfile)"
let "net_threshold *= $time_threshold"
# tell the user how many packets were sent
printf "Network packets sent:\t$packet_sent (diff: $packet_difference/$net_threshold)\n"
# check if the packet count exceeds the threshold set by the user
if (( "$packet_difference" > "$net_threshold" ));
  then
    printf "resetting packet count...\n"
    printf "$packet_sent" > $countfile
  else
    let "datediff = $(date +%s) - $changed"
    let "time_threshold *= 60"
    # tell the user the assumed IDLE time
    printf "IDLE seconds:\t\t$datediff/$time_threshold\n"
    if (( "$datediff" > "$time_threshold" ));
      then
        # are users still logged in?
        if (( "$system_users" > "0" ));
          then
            printf "not suspending because users are logged in.\n";
          else
            # is the CPU occupied?
            if [[ $(echo "$system_load>$load_threshold" | bc) -eq 1 ]];
              then
                printf "not suspending due to CPU load.\n";
              else
                # reset packet counter and suspend
                printf 0 > $countfile
                printf "suspending...\n"
                systemctl suspend
            fi
        fi
    fi
fi

@n1trux -
Your system load parsing does not work on my Centos 7
(my uptime output looks as follows)
19:58:11 up 2:49, 7 users, load average: 0.49, 0.48, 0.55

Here is the code I used which should be more portable across distributions:
system_load=$(cut -d ' ' -f 3 </proc/loadavg)

And for system_users you can simplify to:
system_users=$(w -h | wc -l)