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

I have tried all answers but all of them had one or many problems that I list a few of them.

1. Some detected 123.456.789.111 as valid IP
2. Some don't detect 127.0.00.1 as valid IP
3. Some don't detect IP that start with zero like 08.8.8.8

So here I post a regex that works on all above conditions.

Note : I have extracted more than 2 millions IP without any problem with following regex.

(?:(?:1\d\d|2[0-5][0-5]|2[0-4]\d|0?[1-9]\d|0?0?\d)\.){3}(?:1\d\d|2[0-5][0-5]|2[0-4]\d|0?[1-9]\d|0?0?\d)