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

As other posters pointed out, nmap is the way to go, but here's how to do the equivalent of a ping scan in bash. I wouldn't use the broadcast ping, as a lot of systems are configured not to respond to broadcast ICMP nowadays.

for i in $(seq 1 254); do
    host="192.168.100.$i"
    ping -c 1 -W 1 $host &> /dev/null
    echo -n "Host $host is "
    test $? -eq 0 && echo "up" || echo "down"
done