If you are on a LAN and wish to find out which computers in it currently have access to that certain LAN, you can use the following command:
for ip in $(seq 1 254); do ping -c 1 192.168.1.$ip>/dev/null; [ $? -eq 0 ] && echo “192.168.1.$ip UP” || : ; done
This will ping each computer on the 192.168.1.x subnet one time, with a one second interval between pings. The output should be something like
Alternatively, you can use netdiscover:
sudo apt-get install netdiscover
netdiscover -r 192.168.1.0/24
This will scan all the computers in that particular address range and present the active ones in a table that also provides a MAC address and a MAC Vendor line. Thanks go out to angelblade for this information.