   def put_env(varname, value) when is_binary(varname) and is_binary(value) do
     case :binary.match(varname, "=") do
       {_, _} ->
-        raise ArgumentError, "cannot execute System.put_env/2 for key with \"=\", got: #{inspect varname}"
+        raise ArgumentError,
+              "cannot execute System.put_env/2 for key with \"=\", got: #{inspect(varname)}"
+
       :nomatch ->
-        :os.putenv String.to_charlist(varname), String.to_charlist(value)
+        :os.putenv(String.to_charlist(varname), String.to_charlist(value))
         :ok
     end
   end

  """
  def user_home! do
    user_home() ||
      raise RuntimeError, message: "could not find the user home, please set the HOME environment variable"
  end

  @doc ~S"""

  # the short revision hash. If that fails, returns an empty string.
  defmacrop get_revision do
    null =
      case :os.type() do
        {:win32, _} -> 'NUL'
        _ -> '/dev/null'
      end
