bevy/examples/input/keyboard_input.rs

use bevy::{
    input::{keyboard::KeyCode, Input},
    prelude::*,
};

fn main() {
    App::build()
        .add_default_plugins()
        .add_system(keyboard_input_system.system())
        .run();
}

/// This system prints 'A' key state
fn keyboard_input_system(keyboard_input: Res<Input<KeyCode>>) {
    if keyboard_input.pressed(KeyCode::A) {
        println!("'A' currently pressed");
    }

    if keyboard_input.just_pressed(KeyCode::A) {
        println!("'A' just pressed");
    }

    if keyboard_input.just_released(KeyCode::A) {
        println!("'A' just released");
    }
}