You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: help.go
    path of file: ./repos/yaegi/cmd/yaegi
    
    the code of the file until where you have to start completion: package main

import "fmt"

const usage = `Yaegi is a Go interpreter.

Usage:

    yaegi [command] [arguments]

The commands are:

    extract     gene
    
func help(arg []string) error {
	var cmd string
	if len(arg) > 0 {
		cmd = arg[0]
	}

	switch cmd {
	case Extract:
		return extractCmd([]string{"-h"})
	case Help, "", "-h", "--help":
		fmt.Print(usage)
		return nil
	case Run:
		return run([]string{"-h"})
	case Test:
		return test([]string{"-h"})
	case Version:
		fmt.Println("Usage: yaegi version")
		return nil
	default:
		return fmt.Errorf("help: invalid yaegi command: %v", cmd)
	}
}