Check for IP validity

Question

How do I check the validity of an IP address in a shell script, that is within the range 0.0.0.0 to 255.255.255.255?

Answer 1

This single regex should validate only those addresses between 0.0.0.0 and 255.255.255.255:

#!/bin/bash

ip="1.2.3.4"

if [[ "$ip" =~ ^(([1-9]?[0-9]|1[0-9][0-9]|2([0-4][0-9]|5[0-5]))\.){3}([1-9]?[0-9]|1[0-9][0-9]|2([0-4][0-9]|5[0-5]))$ ]]; then
  echo "success"
else
  echo "fail"
fi