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

Everyone here is using really long-handed regular expressions but actually understanding the regex of POSIX will allow you to use a small grep command like this for printing IP addresses.

grep -Eo "(([0-9]{1,3})\.){3}([0-9]{1,3})"

(Side note) This doesn't ignore invalid IPs but it is very simple.