mixer: avoid extra output when mixer fails

Disable automatic print of errors and usage information from Cobra,
and only print usage information if it was a command / parsing flag
issue.

This also fixes the duplicate errors in current code (both our code
and cobra ware printing errors).

Signed-off-by: Caio Marcelo de Oliveira Filho <[email protected]>

mixer/cmd/root.go

@@ -19,6 +19,7 @@ import (
 	"os"
 	"os/exec"
 	"strconv"
+	"strings"
 
 	"github.com/clearlinux/mixer-tools/builder"
 
@@ -31,6 +32,9 @@ var config string
 var RootCmd = &cobra.Command{
 	Use:  "mixer",
 	Long: `Mixer is a tool used to compose OS update content and images.`,
+
+	SilenceUsage:  true,
+	SilenceErrors: true,
 }
 
 type initCmdFlags struct {
@@ -54,11 +58,33 @@ var initCmd = &cobra.Command{
 	},
 }
 
+var parseErrorPrefixes = []string{
+	"unknown command \"",
+	"unknown flag:",
+	"unknown shorthand flag:",
+	"invalid argument \"",
+	"flag needs an argument:",
+	"bad flag syntax:",
+}
+
 // Execute adds all child commands to the root command and sets flags appropriately.
 // This is called by main.main(). It only needs to happen once to the rootCmd.
 func Execute() {
-	if err := RootCmd.Execute(); err != nil {
-		fmt.Fprintf(os.Stderr, "Mixer Error: %s\n", err)
+	cmd, err := RootCmd.ExecuteC()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "ERROR: %s\n", err)
+
+		// Automatically show usage information if it is a flag parsing error.  Flag parsing
+		// doesn't return errors that we can use types or interfaces to match, so do an
+		// approximation.
+		s := err.Error()
+		for _, p := range parseErrorPrefixes {
+			if strings.HasPrefix(s, p) {
+				cmd.Println()
+				cmd.Print(cmd.UsageString())
+				break
+			}
+		}
 		os.Exit(1)
 	}
 }