#!/usr/bin/env ruby

# minimum length for a password
MINIMUM_LENGTH = 4
# default length if not specified on command line
DEFAULT_LENGTH = 16
# sets of characters to use - don't use 0 and 1 to avoid confusion with O and I
CHARACTER_SETS = [('A'..'Z'),('a'..'z'),('2'..'9')]

# don't change this
characters = CHARACTER_SETS.collect{|set| set.collect{|character| character}}.flatten

length = (ARGV[0] || DEFAULT_LENGTH).to_i
raise ArgumentError, "length of #{length} is too short" unless length >= MINIMUM_LENGTH

password = (0..length-1).inject(''){|pw, n| pw + characters[rand(characters.length)] }
puts password