How do you extract IP addresses from files using a regex in a linux shell?

Question

How to extract a text part by regexp in linux shell? Lets say, I have a file where in every line is an IP address, but on a different position. What is the simplest way to e

Answer 1

for centos6.3

ifconfig eth0 | grep 'inet addr' | awk '{print $2}' | awk 'BEGIN {FS=":"} {print $2}'