Commands

Commands are Minecraft's way of handling text-based user input outside of standard gameplay

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Registering a command

In order to register commands, we first need to listen for Fabric API's command registration event.

public class MyCommandsMod implements DedicatedServerModInitializer {
    @Override
    public void onInitializeServer() {
        CommandRegistrationCallback.EVENT.register(dispatcher, dedicated -> {
            // Add command registration code here
        });
    }
}

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Creating our command

Minecraft commands use Mojang's brigadier library.

Registering a basic command is as follows:

public class MyCommandsMod implements DedicatedServerModInitializer {
    @Override
    public void onInitializeServer() {
        CommandRegistrationCallback.EVENT.register(dispatcher, dedicated -> {
            dispatcher.register(
                    literal("mymodcommand")
                            .executes(ctx -> {
                                ctx.getSource().getPlayer().sendMessage(new LiteralText("IT WORKS"), false);
                                return 1;
                            })
            );
        });
    }
}

If you now run your server and type /mymodcommand you will see a message appear in game chat!

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Arguments

Above, you were introduced to basic registration of commands. We will now make our command more advanced: using arguments.

public class MyCommandsMod implements DedicatedServerModInitializer {
    @Override
    public void onInitializeServer() {
        CommandRegistrationCallback.EVENT.register(dispatcher, dedicated -> {
            dispatcher.register(
                    literal("mymodcommand")
                            .then(literal("subcommand")
                                    .executes(ctx -> {
                                        ctx.getSource().getPlayer().sendMessage(new LiteralText("It works"), false);
                                        return 1;
                                    })
                            )
            );
        });
    }
}

/mymodcommand subcommand will now run the same as /mymodcommand had in the previous example

But what does the code do?

Let's take a look line-by-line

dispatcher.register(

This line tells Minecraft to register the command supplied in the argument of the register method.

literal("mymodcommand")

Here we call CommandManager#literal with the argument "mymodcommand". Literal means that the first part of the command is the string provided.

.then(literal("subcommand")

We add the next part of the command, a string literal with the value subcommand.

.executes(ctx -> {
    ctx.getSource().getPlayer().sendMessage(new LiteralText("It works!"), false);
    return 1;
})

.executes tells Minecraft to run the lambda block provided, taking one lambda parameter: an object of type CommandContext<ServerCommandSource>. It requires an integer to be returned.

Formatting of commands

It's suggested to indent your commands in a way that the various commands and arguments are clearly visible at a glance. IntelliJ's autoformatting tool (CTRL+ALT+L) will help with this.

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Non-String-Literal arguments

String literals provide an excellent way to tell the game which command you are running, as you wouldn't type /minecraft:overworld. We do however want users to be able to enter their own information. Let's take a look at Mojang provided argument types.

public class MyCommandsMod implements DedicatedServerModInitializer {
    @Override
    public void onInitializeServer() {
        CommandRegistrationCallback.EVENT.register(dispatcher, dedicated -> {
            dispatcher.register(
                    literal("count")
                            .then(argument("number", IntegerArgumentType.integer())
                                    .executes(ctx -> {
                                        ctx.getSource().getPlayer().sendMessage(new LiteralText("You entered: " + IntegerArgumentType.getInteger(ctx, "count")), false);
                                        return 1;
                                    })
                            )
                            .then(literal("subcommand")
                                    .executes(ctx -> {
                                        ctx.getSource().getPlayer().sendMessage(new LiteralText("It works"), false);
                                        return 1;
                                    })
                            )
            );
        });
    }
}

As you can see, we duplicated our code and replaced the string literal with a call to CommandManager#argument, providing the name of the argument and the type of the argument. We then obtain that argument using the CommandContext provided in our lambda.

This would leave you with the option of the two commands below:

/count subcommand -> "It works"

/count <count> -> "You entered: "

Arguments Types

Vanilla provides many argument types to use in commands. It's also possible to register your own argument types, but this does not work serverside. You can create pseudo argument types with a string argument type and a custom suggester.

Vanilla Argument Types

• EntityArgumentType
• GameProfileArgumentType
• BlockPosArgumentType
• ColumnPosArgumentType
• Vec3ArgumentType
• Vec2ArgumentType
• BlockStateArgumentType
• BlockPredicateArgumentType
• ItemStackArgumentType
• ItemPredicateArgumentType
• ColorArgumentType
• TextArgumentType
• MessageArgumentType
• NbtCompoundArgumentType
• NbtElementArgumentType
• NbtPathArgumentType
• ScoreboardObjectiveArgumentType
• ScoreboardCriterionArgumentType
• OperationArgumentType
• ParticleEffectArgumentType
• AngleArgumentType
• RotationArgumentType
• ScoreboardSlotArgumentType
• ScoreHolderArgumentType
• SwizzleArgumentType
• TeamArgumentType
• ItemSlotArgumentType
• IdentifierArgumentType
• StatusEffectArgumentType
• CommandFunctionArgumentType
• EntityAnchorArgumentType
• IntRangeArgumentType
• FloatRangeArgumentType
• EnchantmentArgumentType
• EntitySummonArgumentType
• DimensionArgumentType
• TimeArgumentType
• UuidArgumentType

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Congratulations! You learnt how to create a command in your mod. You can now learn to add permission checks to your commands on the Permissions page