Talking to the world
A useful program reads input (from the keyboard, a file, a network call, or another program) and produces output (to the screen, a file, or another network call). Rust provides simple helpers for the basic cases and powerful libraries for the rest.
use std::io::{self, BufRead};
let mut line = String::new();
io::stdin().lock().read_line(&mut line).unwrap();
println!("Hello, {}", line.trim());Buffering and performance
Reading or writing one byte at a time is usually slow. Rust buffers I/O behind the scenes so that small reads and writes are batched into larger ones. When you need maximum performance — large log files, streaming uploads — drop down to the buffered or streaming APIs explicitly.
Closing resources
Files, sockets and database connections must be closed when you are done with them. Forgetting leaks operating-system resources and eventually crashes long-running programs. Use the language's built-in with / using / defer construct (it has a different name in each language) to guarantee cleanup happens.