use std::fs::File;
use std::io::Read;
use std::io::Write;

fn main() {
    let mut data = String::new();
    let mut f = File::open("./README.md").unwrap();
    f.read_to_string(&mut data).unwrap();
    println!("{}", data);

    let mut data2 = format!("hello {}", data);
    let mut f = File::create("./README.md").unwrap();
    f.write_all(&mut data2.as_bytes()).unwrap();
}