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

If you want to provide a list of hosts it can be done with nmap, grep and awk.

Install nmap:

$ sudo apt-get install nmap

Create file hostcheck.sh like this:

hostcheck.sh

#!/bin/bash

nmap -sP -iL hostlist -oG pingscan > /dev/null
grep Up pingscan | awk '{print $2}' > uplist
grep Down pingscan | awk '{print $2}' > downlist

-sP: Ping Scan - go no further than determining if host is online

-iL : Input from list of hosts/networks

-oG : Output scan results in Grepable format, to the given filename.

/dev/null : Discards output

Change the access permission:

$ chmod 775 hostcheck.sh

Create file hostlist with the list of hosts to be checked (hostname or IP):

hostlist (Example)

192.168.1.1-5
192.168.1.101
192.168.1.123

192.168.1.1-5 is a range of IPs

Run the script:

./hostcheck.sh hostfile

Will be generated files pingscan with all the information, uplist with the hosts online (Up) and downlist with the hosts offline (Down).

uplist (Example)

192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.101

downlist (Example)

192.168.1.5
192.168.1.123