File.copy-exclamation-mark

You're seeing just the function copy-exclamation-mark, go back to File module for more information.

copy!(source, destination, bytes_count \\ :infinity)

copy!(Path.t() | io_device(), Path.t() | io_device(), pos_integer() | :infinity) ::
  non_neg_integer()

The same as copy/3 but raises a File.CopyError exception if it fails. Returns the bytes_copied otherwise.