fn main() {
  let search_term = "picture";
  let quote = "Every face, every shop, bedroom window, public-house, and
dark square is a picture feverishly turned--in search of what?
It is the same with books. What do we seek through millions of pages?";

  for (idx, line) in quote.lines().enumerate() {
    if line.contains(search_term) {
      let line_num = idx + 1;
      println!("{}: {}", line_num, line); // <2>
    }
  }
}