   def get_pid, do: iolist_to_binary(:os.getpid)
 
   @doc """
+  Set an environment variable value.
+
   Sets a new `value` for the environment variable `varname`.
   """
   @spec put_env(binary, binary) :: :ok

  end

  @doc """
  Registers a function that will be invoked
  at the end of program execution. Useful for
  invoking a hook in a "script" mode.

  The function must expect the exit status code
  as argument.
  """
  def at_exit(fun) when is_function(fun, 1) do
    :elixir_code_server.cast { :at_exit, fun }
  end

  @doc """
  Executes `command` in a command shell of the target OS,
  captures the standard output of the command and returns
  the result as a binary.

  end

  @doc %S"""
  Writable temporary directory.

  Returns a writable temporary directory.
  Searches for directories in the following order:

  1. The directory named by the TMPDIR environment variable
  2. The directory named by the TEMP environment variable
