use std::fs;
use std::io::prelude::*;
use std::io::BufReader;
let buf = BufReader::new(fs::File::open("log.log").expect("no such file"));
let lines: Vec<String> = buf
    .lines()
    .map(|l| l.expect("Could not parse line"))
    .collect();
let mut output = String::new();
lines.iter().rev().take(10).rev().for_each(|line| {
    output.push_str(&line);
    output.push('\n');
});