Nmap is short for Network Mapper. It is an open-source Linux command-line tool that is used to scan IP addresses and ports in a network and to detect installed applications.

We have to keep in mind, NMAP is an active tool / scanner. This means whatever you run with nmap can be detected on any network that is being monitored. Keep this in mind. For an initial scan, we will scan a subnet quickly just to see what hosts, if any, respond. 

nmap -n -sn 10.x.x.x/24 -oG - | awk '/Up$/{print $2}'

Quick rundown of options and commands:

• -n turns off reverse name resolution, since you just want IP addresses. On a local LAN this is probably the slowest step, too, so you get a good speed boost.
• -sn means “Don’t do a port scan.” It’s the same as the older, deprecated -sP with the mnemonic “ping scan.”
• -oG - sends “grepable” output to stdout, which gets piped to awk.
• /Up$/ selects only lines which end with “Up”, representing hosts that are online.
• {print $2} prints the second whitespace-separated field, which is the IP address.

You can accomplish the same output by also using a combination of awk and cut

We can accomplish the same results above with the following command below using cut.

nmap -n -sn 10.1.80.0/24 -oG - | grep Up$ | cut -d ' ' -f 2

Quick rundown of the command:

• -n turns off reverse name resolution, since you just want IP addresses. On a local LAN this is probably the slowest step, too, so you get a good speed boost.
• -sn means “Don’t do a port scan.” It’s the same as the older, deprecated -sP with the mnemonic “ping scan.”
• -oG - sends “grepable” output to stdout, which gets piped to cut.
• grep Up$ selects only lines which end with “Up”, representing hosts that are online.
• {cut -d ' ' -f 2} prints the second whitespace-separated field, which is the IP address.