mkpwd.rb

#!/usr/bin/ruby
# -*- mode: ruby; coding: utf-8 -*-

pwlength = ARGV.shift&.to_i || 64
pwlength = 64 if pwlength < 1

converter_symbols = ARGV.shift&.each_char

converter = converter_symbols ? ("a" .. "z").to_a + ("A" .. "Z").to_a + ("0" .. "9").to_a +  converter_symbols : ('!' .. '~').to_a

convloops = 255 / converter.length
convlength = converter.length * convloops

File.open("/dev/urandom", "r") do |f|
  pwlength.times do |i|
    c = f.readbyte
    redo if c >= convlength
    print(converter[c % converter.length])
  end
end