func (c *bootstrapCommand) Init(args []string) (err error) {
	if c.showClouds && c.showRegionsForCloud != "" {
		return errors.New("--clouds and --regions can't be used together")
	}
	if c.showClouds {
		return cmd.CheckEmpty(args)
	}
	if c.showRegionsForCloud != "" {
		return cmd.CheckEmpty(args)
	}
	if c.AgentVersionParam != "" && c.BuildAgent {
		return errors.New("--agent-version and --build-agent can't be used together")
	}
	if c.BootstrapSeries != "" && !charm.IsValidSeries(c.BootstrapSeries) {
		return errors.NotValidf("series %q", c.BootstrapSeries)
	}

	// Parse the placement directive. Bootstrap currently only
	// supports provider-specific placement directives.
	if c.Placement != "" {
		_, err = instance.ParsePlacement(c.Placement)
		if err != instance.ErrPlacementScopeMissing {
			// We only support unscoped placement directives for bootstrap.
			return errors.Errorf("unsupported bootstrap placement directive %q", c.Placement)
		}
	}
	if !c.AutoUpgrade {
		// With no auto upgrade chosen, we default to the version matching the bootstrap client.
		vers := jujuversion.Current
		c.AgentVersion = &vers
	}
	if c.AgentVersionParam != "" {
		if vers, err := version.ParseBinary(c.AgentVersionParam); err == nil {
			c.AgentVersion = &vers.Number
		} else if vers, err := version.Parse(c.AgentVersionParam); err == nil {
			c.AgentVersion = &vers
		} else {
			return err
		}
	}
	if c.AgentVersion != nil && (c.AgentVersion.Major != jujuversion.Current.Major || c.AgentVersion.Minor != jujuversion.Current.Minor) {
		return errors.New("requested agent version major.minor mismatch")
	}

	switch len(args) {
	case 0:
		// no args or flags, go interactive.
		c.interactive = true
		return nil
	}
	c.Cloud = args[0]
	if i := strings.IndexRune(c.Cloud, '/'); i > 0 {
		c.Cloud, c.Region = c.Cloud[:i], c.Cloud[i+1:]
	}
	if len(args) > 1 {
		c.controllerName = args[1]
		return cmd.CheckEmpty(args[2:])
	}
	return nil
}

func (c *restoreCommand) Init(args []string) error {
	if c.showDescription {
		return cmd.CheckEmpty(args)
	}
	if len(args) == 0 {
		return fmt.Errorf("no backup file specified")
	}
	c.backupFile = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *JenvCommand) Init(args []string) error {
	if len(args) == 0 {
		return errors.New("no jenv file provided")
	}

	// Store the path to the jenv file.
	if err := c.jenvFile.Set(args[0]); err != nil {
		return errors.Annotate(err, "invalid jenv path")
	}
	args = args[1:]

	if len(args) > 0 {
		// Store and validate the provided environment name.
		c.envName, args = args[0], args[1:]
		if !names.IsValidUser(c.envName) {
			return errors.Errorf("invalid model name %q", c.envName)
		}
	} else {
		// Retrieve the environment name from the jenv file name.
		base := filepath.Base(c.jenvFile.Path)
		c.envName = base[:len(base)-len(filepath.Ext(base))]
	}

	// No other arguments are expected.
	return cmd.CheckEmpty(args)
}

// Init implements Command.Init.
func (c *removeCommand) Init(args []string) error {
	if len(args) == 0 {
		return errors.Errorf("no username supplied")
	}
	c.UserName = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *RunCommand) Init(args []string) error {
	// make sure we aren't in an existing hook context
	if contextId, err := getenv("JUJU_CONTEXT_ID"); err == nil && contextId != "" {
		return fmt.Errorf("juju-run cannot be called from within a hook, have context %q", contextId)
	}
	if !c.noContext {
		if len(args) < 1 {
			return fmt.Errorf("missing unit-name")
		}
		var unitName string
		unitName, args = args[0], args[1:]
		// If the command line param is a unit id (like service/2) we need to
		// change it to the unit tag as that is the format of the agent directory
		// on disk (unit-service-2).
		if names.IsValidUnit(unitName) {
			c.unit = names.NewUnitTag(unitName)
		} else {
			var err error
			c.unit, err = names.ParseUnitTag(unitName)
			if err != nil {
				return errors.Trace(err)
			}
		}
	}
	if len(args) < 1 {
		return fmt.Errorf("missing commands")
	}
	c.commands, args = args[0], args[1:]
	return cmd.CheckEmpty(args)
}

func (c *UpgradeJujuCommand) Init(args []string) error {
	if c.vers != "" {
		vers, err := version.Parse(c.vers)
		if err != nil {
			return err
		}
		if vers.Major != version.Current.Major {
			return fmt.Errorf("cannot upgrade to version incompatible with CLI")
		}
		if c.UploadTools && vers.Build != 0 {
			// TODO(fwereade): when we start taking versions from actual built
			// code, we should disable --version when used with --upload-tools.
			// For now, it's the only way to experiment with version upgrade
			// behaviour live, so the only restriction is that Build cannot
			// be used (because its value needs to be chosen internally so as
			// not to collide with existing tools).
			return fmt.Errorf("cannot specify build number when uploading tools")
		}
		c.Version = vers
	}
	if len(c.Series) > 0 && !c.UploadTools {
		return fmt.Errorf("--series requires --upload-tools")
	}
	return cmd.CheckEmpty(args)
}

func (c *addCredentialCommand) Init(args []string) (err error) {
	if len(args) < 1 {
		return errors.New("Usage: juju add-credential <cloud-name> [-f <credentials.yaml>]")
	}
	c.CloudName = args[0]
	return cmd.CheckEmpty(args[1:])
}

// SetFlags implements Command.Init.
func (c *useEnvironmentCommand) Init(args []string) error {
	if len(args) == 0 || strings.TrimSpace(args[0]) == "" {
		return errors.New("no environment supplied")
	}

	name, args := args[0], args[1:]

	// First check to see if an owner has been specified.
	bits := strings.SplitN(name, "/", 2)
	switch len(bits) {
	case 1:
		// No user specified
		c.EnvName = bits[0]
	case 2:
		owner := bits[0]
		if names.IsValidUser(owner) {
			c.Owner = owner
		} else {
			return errors.Errorf("%q is not a valid user", owner)
		}
		c.EnvName = bits[1]
	}

	// Environment names can generally be anything, but we take a good
	// stab at trying to determine if the user has specified a UUID
	// instead of a name. For now, we only accept a properly formatted UUID,
	// which means one with dashes in the right place.
	if names.IsValidEnvironment(c.EnvName) {
		c.EnvUUID, c.EnvName = c.EnvName, ""
	}

	return cmd.CheckEmpty(args)
}

func (c *exposeCommand) Init(args []string) error {
	if len(args) == 0 {
		return errors.New("no application name specified")
	}
	c.ApplicationName = args[0]
	return cmd.CheckEmpty(args[1:])
}

// Init is part of the cmd.Command interface.
func (c *RelationGetCommand) Init(args []string) error {
	if c.RelationId == -1 {
		return fmt.Errorf("no relation id specified")
	}
	c.Key = ""
	if len(args) > 0 {
		if c.Key = args[0]; c.Key == "-" {
			c.Key = ""
		}
		args = args[1:]
	}
	name, err := c.ctx.RemoteUnitName()
	if err == nil {
		c.UnitName = name
	} else if cause := errors.Cause(err); !errors.IsNotFound(cause) {
		return errors.Trace(err)
	}
	if len(args) > 0 {
		c.UnitName = args[0]
		args = args[1:]
	}
	if c.UnitName == "" {
		return fmt.Errorf("no unit id specified")
	}
	return cmd.CheckEmpty(args)
}

// Init implements Command.
func (c *dumpDBCommand) Init(args []string) error {
	if len(args) == 1 {
		c.model = args[0]
		return nil
	}
	return cmd.CheckEmpty(args)
}

func (c *portCommand) Init(args []string) error {
	if args == nil {
		return errors.New("no port specified")
	}
	parts := strings.Split(args[0], "/")
	if len(parts) > 2 {
		return fmt.Errorf("expected %s; got %q", portFormat, args[0])
	}
	port, err := strconv.Atoi(parts[0])
	if err != nil {
		return badPort(parts[0])
	}
	if port < 1 || port > 65535 {
		return badPort(port)
	}
	protocol := "tcp"
	if len(parts) == 2 {
		protocol = strings.ToLower(parts[1])
		if protocol != "tcp" && protocol != "udp" {
			return fmt.Errorf(`protocol must be "tcp" or "udp"; got %q`, protocol)
		}
	}
	c.Port = port
	c.Protocol = protocol
	return cmd.CheckEmpty(args[1:])
}

func (c *ensureAvailabilityCommand) Init(args []string) error {
	if c.NumStateServers < 0 || (c.NumStateServers%2 != 1 && c.NumStateServers != 0) {
		return fmt.Errorf("must specify a number of state servers odd and non-negative")
	}
	if c.PlacementSpec != "" {
		placementSpecs := strings.Split(c.PlacementSpec, ",")
		c.Placement = make([]string, len(placementSpecs))
		for i, spec := range placementSpecs {
			p, err := instance.ParsePlacement(strings.TrimSpace(spec))
			if err == nil && names.IsContainerMachine(p.Directive) {
				return errors.New("ensure-availability cannot be used with container placement directives")
			}
			if err == nil && p.Scope == instance.MachineScope {
				// Targeting machines is ok.
				c.Placement[i] = p.String()
				continue
			}
			if err != instance.ErrPlacementScopeMissing {
				return fmt.Errorf("unsupported ensure-availability placement directive %q", spec)
			}
			c.Placement[i] = spec
		}
	}
	return cmd.CheckEmpty(args)
}

// Init is part of the cmd.Command interface.
func (c *applicationVersionSetCommand) Init(args []string) error {
	if len(args) < 1 {
		return errors.New("no version specified")
	}
	c.version = args[0]
	return cmd.CheckEmpty(args[1:])
}

// Init implements Command.Init.
func (c *DisenableUserBase) Init(args []string) error {
	if len(args) == 0 {
		return errors.New("no username supplied")
	}
	c.user = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *publishCommand) Init(args []string) error {
	if len(args) == 0 {
		return nil
	}
	c.URL = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *UnexposeCommand) Init(args []string) error {
	if len(args) == 0 {
		return errors.New("no service name specified")
	}
	c.ServiceName = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *debugLogCommand) Init(args []string) error {
	if c.level != "" {
		level, ok := loggo.ParseLevel(c.level)
		if !ok || level < loggo.TRACE || level > loggo.ERROR {
			return errors.Errorf("level value %q is not one of %q, %q, %q, %q, %q",
				c.level, loggo.TRACE, loggo.DEBUG, loggo.INFO, loggo.WARNING, loggo.ERROR)
		}
		c.params.Level = level
	}
	if c.tail && c.notail {
		return errors.NotValidf("setting --tail and --no-tail")
	}
	if c.utc {
		c.tz = time.UTC
	}
	if c.date {
		c.format = "2006-01-02 15:04:05"
	} else {
		c.format = "15:04:05"
	}
	if c.ms {
		c.format = c.format + ".000"
	}
	return cmd.CheckEmpty(args)
}

func (c *BootstrapCommand) Init(args []string) (err error) {
	if len(c.Series) > 0 && !c.UploadTools {
		return fmt.Errorf("--upload-series requires --upload-tools")
	}
	if len(c.seriesOld) > 0 && !c.UploadTools {
		return fmt.Errorf("--series requires --upload-tools")
	}
	if len(c.Series) > 0 && len(c.seriesOld) > 0 {
		return fmt.Errorf("--upload-series and --series can't be used together")
	}
	if len(c.seriesOld) > 0 {
		c.Series = c.seriesOld
	}

	// Parse the placement directive. Bootstrap currently only
	// supports provider-specific placement directives.
	if c.Placement != "" {
		_, err = instance.ParsePlacement(c.Placement)
		if err != instance.ErrPlacementScopeMissing {
			// We only support unscoped placement directives for bootstrap.
			return fmt.Errorf("unsupported bootstrap placement directive %q", c.Placement)
		}
	}
	return cmd.CheckEmpty(args)
}

func (c *MigrateCommand) Init(args []string) error {
	if len(args) == 0 {
		return errors.New("missing operation")
	}
	c.operation, args = args[0], args[1:]

	switch c.operation {
	case "export":
		if len(args) == 0 {
			return errors.New("missing model uuid")
		}
		c.modelUUID, args = args[0], args[1:]

	case "import":
		if len(args) == 0 {
			return errors.New("missing yaml filename")
		}
		c.filename, args = args[0], args[1:]
	default:
		return errors.Errorf("unknown operation %q", c.operation)
	}

	if !names.IsValidMachine(c.machineId) {
		return errors.Errorf("%q is not a valid machine id", c.machineId)
	}
	c.machineTag = names.NewMachineTag(c.machineId)
	return cmd.CheckEmpty(args)
}