cli

 $ mkpasswd -m sha-512 poop dd3s05pu
$6$dd3s05pu$hBxcrWHy1tKBDrrDZPYlnWS81JJNlimgGxukyUgNgbf6fopwFDQIvAKVYu6XXALPISmbxCWRY4hL6xjCaF7IG/

ruby.rb

class User < Struct.new(:username, :password, :uid, :gid)
  def hashed_password()
    password.crypt("$6$" + salt)
  end

  def salt
    @salt || rand(36**8).to_s(36)
  end

  def salt=(s)
    @salt = s
  end

  def passwd_line
    [username,
     hashed_password,
     uid,
     gid,
     gecos,
     homedir,
     shell
    ].join(':')
  end

  def homedir
    "#{ftp_root}/#{username}"
  end

  def shell
  end

  def ftp_root
    '/mnt/ftp'
  end

  def gecos
    nil
  end
end