read lines - Rust By Example
Description: A description

# `read_lines`

The method `lines()` returns an iterator over the lines of a file.

`File::open` expects a generic, `AsRef<Path>`. That's what `read_lines()` expects as input.

    use std::fs::File;
    use std::io::{self, BufRead};
    use std::path::Path;

    fn main() {
        // File hosts must exist in current path before this produces output
        if let Ok(lines) = read_lines("./hosts") {
            // Consumes the iterator, returns an (Optional) String
            for line in lines {
                if let Ok(ip) = line {
                    println!("{}", ip);
                }
            }
        }
    }

    // The output is wrapped in a Result to allow matching on errors
    // Returns an Iterator to the Reader of the lines of the file.
    fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
    where P: AsRef<Path>, {
        let file = File::open(filename)?;
        Ok(io::BufReader::new(file).lines())
    }

Running this program simply prints the lines individually.

    $ echo -e "127.0.0.1\n192.168.0.1\n" > hosts
    $ rustc read_lines.rs && ./read_lines
    127.0.0.1
    192.168.0.1

This process is more efficient than creating a `String` in memory especially working with larger files.