exit with status 1 if help is called on an invalid command.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

cobra.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/spf13/cobra"
 )
@@ -17,6 +18,7 @@ func SetupRootCommand(rootCmd *cobra.Command) {
 	rootCmd.SetUsageTemplate(usageTemplate)
 	rootCmd.SetHelpTemplate(helpTemplate)
 	rootCmd.SetFlagErrorFunc(FlagErrorFunc)
+	rootCmd.SetHelpCommand(helpCommand)
 
 	rootCmd.PersistentFlags().BoolP("help", "h", false, "Print usage")
 	rootCmd.PersistentFlags().MarkShorthandDeprecated("help", "please use --help")
@@ -39,6 +41,23 @@ func FlagErrorFunc(cmd *cobra.Command, err error) error {
 	}
 }
 
+var helpCommand = &cobra.Command{
+	Use:               "help [command]",
+	Short:             "Help about the command",
+	PersistentPreRun:  func(cmd *cobra.Command, args []string) {},
+	PersistentPostRun: func(cmd *cobra.Command, args []string) {},
+	RunE: func(c *cobra.Command, args []string) error {
+		cmd, args, e := c.Root().Find(args)
+		if cmd == nil || e != nil || len(args) > 0 {
+			return fmt.Errorf("unknown help topic: %v", strings.Join(args, " "))
+		}
+
+		helpFunc := cmd.HelpFunc()
+		helpFunc(cmd, args)
+		return nil
+	},
+}
+
 func hasSubCommands(cmd *cobra.Command) bool {
 	return len(operationSubCommands(cmd)) > 0
 }