Searching IP address in a text file or a console output may become cumbersome. This little command named grep will help you in this way.

Example Data

We have a file or output which includes the IP address and we want to extract just IP addresses nothing other. This file is created with a nmap scan.

Nmap scan report for 192.168.122.1 
Host is up (0.00022s latency). 
Nmap scan report for kali (192.168.122.126) 
Host is up (0.00015s latency).

Print Interfaces IP Addresses

We can use ip addr command which will print current system interfaces and related information. We can grep from this information and print only IP addresses currently the system is using with the following command.

$ ip add | grep -o -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'

Print Only IP Addresses

Here we use grep command and give -o option to only get the IP address. The default behavior of the grep is printing lines which match given regex but if we only want to print matched text not the whole line we will use -o option which will print only IP addresses.

$ grep -o -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' network_list.txt 
192.168.122.1 
192.168.122.126

Grep and Filter IP Address In Linux Infografic