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

Assuming my network is 10.10.0.0/24, if i run a ping on the broadcast address like

ping -b 10.10.0.255

I'll get an answer from all computers on this network that did not block their ICMP ping port.

64 bytes from 10.10.0.6: icmp_seq=1 ttl=64 time=0.000 ms
64 bytes from 10.10.0.12: icmp_seq=1 ttl=64 time=0.000 ms 
64 bytes from 10.10.0.71: icmp_seq=1 ttl=255 time=0.000 ms 

So you just have to extract the 4th column, with awk for example:

ping -b 10.10.0.255 | grep 'bytes from' | awk '{ print $4 }'

10.10.0.12:
10.10.0.6:
10.10.0.71:
10.10.0.95:

Well, you will get duplicate, and you may need to remove the ':'.

EDIT from comments : the -c option limits the number of pings since the script will end, we can also limit ourself on unique IPs

ping -c 5 -b 10.10.0.255 | grep 'bytes from' | awk '{ print $4 }' | sort | uniq