# Shell completion

Cliffy supports shell completion out of the box. To enable shell completions it
is required to register the
[completions](./build_in_commands.md#completions-command) command.

The completions command generates a shell completions script for your specific
shell environment. Currently supported shells are:

- [bash](./build_in_commands.md#bash-completions)
- [fish](./build_in_commands.md#fish-completions)
- [zsh](./build_in_commands.md#zsh-completions)

The completions script enables completions for all sub-commands, options and
arguments.

There are three ways to add shell completions to types which are explained in
the following sections.

## Enum type

One way is to use the `EnumType`. All values defined with the `EnumType` will be
used for shell completions. Read more about the enum type
[here](./types.md#enum-type).

```typescript
import { Command, EnumType } from "https://deno.land/x/cliffy/command/mod.ts";

const colorType = new EnumType(["red", "blue", "yellow"]);

await new Command()
  .type("color", colorType)
  .arguments("[color-name:color]")
  .option("-c, --color <name:color>", "Choose a color.")
  .parse(Deno.args);
```

## Complete method

Another way to add completions is by registering a completions action with the
`.complete()` method. The values returned by the `.complete()` method will be
used for shell completions.

To use these completions you can add the name of the action after the type
separated by colon.

> ❗ Completions defined with the `.complete()` method will override the
> completions defined with a type.

```typescript
import { Command } from "https://deno.land/x/cliffy/command/mod.ts";

await new Command()
  .complete("color", () => ["red", "blue", "yellow"])
  .arguments("[color-name:string:color]")
  .option("-c, --color <name:string:color>", "Choose a color.")
  .parse(Deno.args);
```

## Custom type

The 3rd way to add shell completions is by creating a custom type with a
`.complete()` method. The values returned by the `.complete()` method will be
used for shell completions. You can read more about custom types
[here](./types.md#custom-types).

```typescript
import { Command, StringType } from "https://deno.land/x/cliffy/command/mod.ts";

class ColorType extends StringType {
  complete(): Array<string> {
    return ["red", "blue", "yellow"];
  }
}

await new Command()
  .type("color", new ColorType())
  .option("-c, --color <name:color>", "Choose a color.")
  .parse(Deno.args);
```