When a Process goes out of scope, its drop method will wait until the
child process finishes before releasing the resource.
// wait.rs
use std::io::process::Command;
fn main() {
let _process = Command::new("sleep").arg("5").spawn();
println!("reached end of main");
}
$ rustc wait.rs && ./wait
reached end of main
# `wait` keeps running for 5 seconds
# `sleep 5` command ends, and then our `wait` program finishes