#!/usr/bin/perl
use strict;
my $ip = $ARGV[0] or die "Usage: $0 IP\n";
# Define the valid range from 0 to 255 for each number in the IP
# Read regexp as "valid for 0-9 or 10-99 or 100-199 or 200-249 or 250-255"
my $valid_number = '(\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])';
# Join for valid numbers with dots
my $valid = ($ip =~ m/^$valid_number\.$valid_number\.$valid_number\.$valid_number$/) ? "valid" : "invalid";
print "$valid\n";