bevy/examples/app/custom_loop.rs

//! This example demonstrates you can create a custom runner (to update an app manually). It reads
//! lines from stdin and prints them from within the ecs.

use bevy::prelude::*;
use std::io;

#[derive(Resource)]
struct Input(String);

fn my_runner(mut app: App) {
    println!("Type stuff into the console");
    for line in io::stdin().lines() {
        {
            let mut input = app.world_mut().resource_mut::<Input>();
            input.0 = line.unwrap();
        }
        app.update();
    }
}

fn print_system(input: Res<Input>) {
    println!("You typed: {}", input.0);
}

fn main() {
    App::new()
        .insert_resource(Input(String::new()))
        .set_runner(my_runner)
        .add_systems(Update, print_system)
        .run();
}