How can I write a Linux bash script that tells me which computers are ON in my LAN?

Question

How can I write a Linux Bash script that tells me which computers are ON in my LAN?

It would help if I could give it a range of IP addresses as input.

Answer 1

Although an old question, it still seems to be important (at least important enough for me to deal with this). My script relies on nmap too, so nothing special here except that ou can define which interface you want to scan and the IP Range is created automagically (at least kind of).

This is what I came up with

#!/bin/bash
#Script for scanning the (local) network for other computers 

command -v nmap >/dev/null 2>&1 || { echo "I require nmap but it's not installed. Aborting." >&2; exit 1; }

if [ -n ""$@"" ];  then
    ip=$(/sbin/ifconfig $1 | grep 'inet '  | awk '{ print $2}' | cut -d"." -f1,2,3 )
    nmap -sP $ip.1-255
else
    echo -e "\nThis is a script for scanning the (local) network for other computers.\n"
    echo "Enter Interface as parameter like this:"
    echo -e "\t./scannetwork.sh $(ifconfig -lu | awk '{print $2}')\n"

    echo "Possible interfaces which are up are: "   
    for i in $(ifconfig -lu)
    do
        echo -e "\033[32m \t $i \033[39;49m"
    done

    echo "Interfaces which could be used but are down at the moment: "
    for i in $(ifconfig -ld)
    do
        echo -e "\033[31m \t $i \033[39;49m"
    done
    echo
fi

One remark: This script is created on OSX, so there might be some changes to linux environments.

Answer 2

The following (evil) code runs more than TWICE as fast as the nmap method

for i in {1..254} ;do (ping 192.168.1.$i -c 1 -w 5  >/dev/null && echo "192.168.1.$i" &) ;done

takes around 10 seconds, where the standard nmap

nmap -sP 192.168.1.1-254

takes 25 seconds...

Answer 3

If you're limiting yourself to only having the last octet changing, this script should do it. It should be fairly obvious how to extend it from one to multiple octets.

#! /bin/bash
BASE=$1
START=$2
END=$3

counter=$START

while [ $counter -le $END ]
do
  ip=$BASE.$counter
  if ping -qc 2 $ip
  then
    echo "$ip responds"
  fi
  counter=$(( $counter + 1 ))
done

Answer 4

Just for fun, here's an alternate

     #!/bin/bash
     nmap -sP 192.168.1.0/24 > /dev/null 2>&1 && arp -an | grep -v incomplete | awk '{print$2}' | sed -e s,\(,, | sed -e s,\),,

Answer 5

#!/bin/bash

for ((n=0 ; n < 30 ; n+=1))
do
    ip=10.1.1.$n
    if ping -c 1 -w 1 $ip > /dev/null 2> /dev/null >> /etc/logping.txt; then  
        echo "${ip} is up" # output up
        # sintax >> /etc/logping.txt log with .txt format
    else
        echo "${ip} is down" # output down
    fi
done

Answer 6

Also using the "ping the broadcast address" method pointed out by chburd, this pipe should do the trick for you:

ping -c 5 -b 10.11.255.255 | sed -n 's/.* \([0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+\).*/\1/p' | sort | uniq

Of course, you'd have to change the broadcast address to that of your network.