command.go
func (c *Command) Arg(v interface{}) *Command {
	c.args = append(c.args, fmt.Sprintf("%v", v))
	return c
}
func (c *Command) Arg(v interface{}) *Command {
	c.args = append(c.args, fmt.Sprintf("%v", v))
	return c
}
// Arg appends a new argument to the command.