When you have entered something into IEx which expects a completion, such as a multiline string, IEx will change the prompt to indicate that it is waiting for you finish by changing the prompt to have an ellipsis (
...) rather than
If you find that IEx is waiting for you to finish an expression but you aren't sure what it needs to terminate the expression, or you simply want to abort this line of input, enter
#iex:break as the console input. This will cause IEx to throw a
TokenMissingError and cancel waiting for any more input, returning you to a standard "top-level" console input.
iex:1> "foo" "foo" iex:2> "bar ...:2> #iex:break ** (TokenMissingError) iex:2: incomplete expression
More info is available at the IEx documentation.