find ip address of my system for a particular interface with shell script (bash)

Question

I am trying to find ip-address of my own system through a shell script and write into a text thats my script content

#!/bin/bash

wifiip=$(ip addr | grep inet | grep wlan0 | awk -F" " '{print $2}'| sed -e 's/\/.*$//')

eth0ip=$(ip addr | grep inet | grep eth0 | awk -F" " '{print $2}' | sed -e 's/\/.*$//')

if [ "$eth0ip" == "0" ]; then

    echo "$eth0ip" | grep [0-9]$ > /home/pi/att/ip.txt

else 

    echo "$wifiip" | grep [0-9]$ > /home/pi/att/ip.txt

fi

and trying to do something like if one interface is not up print another ip in ip.txt

but it's giving

ip.sh: 14: [: unexpected operator 

Answer 1

Let's clean up your code first. You don't need chains of a dozen different commands and pipes when you're already using awk. This:

wifiip=$(ip addr | grep inet | grep wlan0 | awk -F" " '{print $2}'| sed -e 's/\/.*$//')

can be written simply as this:

wifiip=$(ip addr | awk '/inet/ && /wlan0/{sub(/\/.*$/,"",$2); print $2}')

but your whole script can be written as just one awk command.

I need you to update your question with some sample output of the ip addr command, the output you want from the awk command given that input, and explain more clearly what you're trying to do in order to show you the correct way to write that but it might be something like this:

ip addr | awk '
/inet/ { ip[$NF] = $2; sub(/\/.*$/,"",ip[$NF]) }
END { print ( "eth0" in ip ? ip["eth0"] : ip["wlan0"] ) }
' > /home/pi/att/ip.txt

Answer 2

Here is a nice way to get your IP address. This gives you the address used to reach the internet at the test, so it will give you correct IP even if you change from Wifi to eth or to any other IF type.

See more detailed post here: Linux bash script to extract IP address

my_ip=$(ip route get 8.8.8.8 | awk '/8.8.8.8/ {print $NF}')

To get interface name:

my_if=$(ip route get 8.8.8.8 | awk '/dev/ {f=NR} f&&NR-1==f' RS=" ")