bevy-commands

name	bevy-commands
description	Reference for Bevy Commands — spawning/despawning entities, inserting/removing components, custom commands, trait extensions, and testing.
metadata	{"crate":"bevy_ecs","bevy":"0.19"}

Basics

Commands is a system parameter that queues mutations. They execute together at the next schedule transition (via ApplyDeferred).

fn spawn(mut commands: Commands) {
  commands.spawn_empty();
}

Spawning components

commands.spawn(Player).insert(Transform::default());
// or with a tuple bundle
commands.spawn((Player, Transform::from_xyz(1., 1., 1.)));

Required components

#[derive(Component)]
#[require(Transform)]
struct Player;
// now: commands.spawn(Player) auto-adds Transform

EntityCommands chaining

spawn/spawn_empty return EntityCommands for chaining:

commands
  .spawn(Player)
  .insert(Transform::default())
  .insert(Name::new("Player 1"));

Despawning

for entity in &query {
  commands.entity(entity).despawn();
}

Commands are deferred

Commands don't execute immediately — they're queued until the next ApplyDeferred system runs (typically at schedule boundaries).

Custom commands

Implement the Command trait:

struct SpawnPlanet { radius: f32, position: Vec2 }

impl Command for SpawnPlanet {
  fn apply(self, world: &mut World) {
    let mesh = world.resource_scope(|_w, mut meshes: Mut<Assets<Mesh>>| {
      meshes.add(Circle::new(self.radius))
    });
    // ...
    world.spawn((Planet::new(self.radius), Mesh2d(mesh), Transform::from_translation(self.position.extend(0.))));
  }
}
// usage:
commands.queue(SpawnPlanet { radius: 100., position: Vec2::ZERO });

Extending the Commands API

trait MyExt {
  fn do_thing(&mut self);
}
impl<'w, 's> MyExt for Commands<'w, 's> {
  fn do_thing(&mut self) { info!("thing done"); }
}

Testing commands

use bevy::ecs::world::CommandQueue;

let mut world = World::default();
let mut queue = CommandQueue::default();
queue.push(MyCommand);
queue.apply(&mut world);