Redirects are Brigadier's form of aliases and subcommands. The redirect method takes a command node and an optional modifier of context. The command node can be a specific node after a registration of dispathcer, or just the root node.

In vanilla Minecraft, /tell and /w are redirected to /msg, which you can see in MessageCommand.

The example shows how /foo2 redirects to /foo.

public class ExampleMod implements ModInitializer {
  @Override
  public void onInitialize() {
    CommandRegistrationCallback.EVENT.register((dispatcher, registryAccess, environment) -> {
      final LiteralCommandNode<ServerCommandSource> fooNode = dispatcher.register(literal("foo")
          .executes(context -> {
            // For versions below 1.19, replace "Text.literal" with "new LiteralText".
            context.getSource().sendMessage(Text.literal("Called /foo with no arguments"));
 
            return 1;
          }));
      dispatcher.register(literal("foo2").redirect(fooNode));
    });
  }
}

The redirect tells brigadier to continue parsing the command at another command node.

Commands such as /execute as @e[type=player] in the_end run tp ~ ~ ~ are also possible because of redirects.

Let's first consider the vanilla /execute command. There is a node after the literal("execute"). After dispatching subcommands, the dispatcher is redirected to that node (with some modifiers), making you possible to, after completing sub-command arguments, type whatever can be typed directly after /execute. In the sub-command run, the dispatcher is redirected to the root node (dispatcher.getRoot()), allowing you to type another complete command after the word “run”.

Below is an example of a chainable command:

LiteralCommandNode<ServerCommandSource> rootNode = dispatcher.register(literal("fabric_test"));
LiteralCommandNode<ServerCommandSource> root1 = dispatcher.register(literal("fabric_test") 
    // You can register under the same literal more than once, it will just register new parts 
    // of the branch as shown below if you register a duplicate branch an error will popup in 
    // console warning of conflicting commands but one will still work.
    .then(literal("extra")
        .then(literal("long")
            .redirect(rootNode, this::lengthen)) // Return to root for chaining
        .then(literal("short")
            .redirect(rootNode, this::shorten))) // Return to root for chaining
        .then(literal("command")
            .executes(ctx -> {
                ctx.getSource().sendFeedback(Text.literal("Chainable Command"), false);
                return Command.SINGLE_SUCCESS;
})));

The redirect can also modify the CommandSource by use of a “redirect modifier” (SingleRedirectModifier<S>), which is used as a lambda.

.redirect(rootNode, context -> {
    // When redirecting, modify the looking direction of the command source.
    return ((ServerCommandSource) context.getSource()).withLookingAt(Vec3ArgumentType.getVec3(context, "pos"));
})