In a layman’s language, IP addresses can be thought of as house addresses. Just like we have a unique house address for each house, similarly, we have a unique IP address for each unique device on the network. An IP address is used to uniquely identify a device on an internet protocol network.

Example of an IP address:

192.0.2.1/24

Here, 192.0.2.1 is called network ID and 24 is the host ID. We can think of the network ID as a Street name and the host ID is a unique House number.

Writing Shell Script to list all IP addresses

Method 1: Using hostname command:

The hostname is a command which is used to display detailed information about hostname in Linux, hostname is a unique domain name assigned to a computer. You can view your device hostname by writing the hostname command in the terminal. 

Command:

hostname -I

Here, “-I” is used to list all IP addresses.

Output:

ip addresses

Let’s write a script to list all IP.

After getting all the IP, split these IP addresses by space. Display the formatted output.

Script:

#! /bin/bash

# saving all the ip addresses
ip_addresses=$(hostname -I)

# splitting them by space
ip_addresses=(${ip_addresses//" "/ })

# Print each ip address line by line
echo "LIST OF IP ADDRESSES"
for ip in "${ip_addresses[@]}";
do
  printf "$ip\n"
done

Output:

List of ip addresses

Note: hostname -I will not display link-local ip6 address because it is automatically configured for every interface that supports IPv6.

Method 2: Using awk command:

awk is a Turing-complete pattern matching programming language widely used with other Linux commands for pattern matching and data extraction.

Script:

#! /bin/bash

# Extracting lines that match the following pattern 
ip=$(ip address| awk '/inet/ {print $2}' | grep -v ^::1 | grep -v ^127)

#displaying IP addresses
echo "LIST OF IP ADDRESSES"
echo "$ip"

Here ip address will list the information about networks including their ip addresses, using awk ‘/inet/ {printf $2}’ we’re finding patterns that start with inet and printing the addresses. And grep -v ^::1 will invert the match that contains “::1”, similarly we don’t want to list our localhost as an ip address, so we are omitting it using the grep -v ^127.

Output :

List of ip addresses