Customizable error message prefix

command.go

@@ -603,6 +603,18 @@ func (c *Command) VersionTemplate() string {
 `
 }
 
+// ErrPrefix return error message prefix for the command
+func (c *Command) ErrPrefix() string {
+	if c.errPrefix != "" {
+		return c.errPrefix
+	}
+
+	if c.HasParent() {
+		return c.parent.ErrPrefix()
+	}
+	return "Error:"
+}
+
 func hasNoOptDefVal(name string, fs *flag.FlagSet) bool {
 	flag := fs.Lookup(name)
 	if flag == nil {
@@ -1058,7 +1070,7 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 			c = cmd
 		}
 		if !c.SilenceErrors {
-			c.PrintErrln(c.errPrefix, err.Error())
+			c.PrintErrln(c.ErrPrefix(), err.Error())
 			c.PrintErrf("Run '%v --help' for usage.\n", c.CommandPath())
 		}
 		return c, err
@@ -1087,7 +1099,7 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 		// If root command has SilenceErrors flagged,
 		// all subcommands should respect it
 		if !cmd.SilenceErrors && !c.SilenceErrors {
-			c.PrintErrln(c.errPrefix, err.Error())
+			c.PrintErrln(c.ErrPrefix(), err.Error())
 		}
 
 		// If root command has SilenceUsage flagged,

command_test.go

@@ -1099,6 +1099,18 @@ func TestShorthandVersionTemplate(t *testing.T) {
 	checkStringContains(t, output, "customized version: 1.0.0")
 }
 
+func TestErrPrefix(t *testing.T) {
+	rootCmd := &Command{Use: "root", SilenceUsage: true, Run: emptyRun}
+	rootCmd.SetErrPrefix("customized error prefix:")
+
+	output, err := executeCommand(rootCmd, "--unknown", "flag")
+	if err == nil {
+		t.Errorf("Expected error")
+	}
+
+	checkStringContains(t, output, "customized error prefix: unknown flag: --unknown")
+}
+
 func TestVersionFlagExecutedOnSubcommand(t *testing.T) {
 	rootCmd := &Command{Use: "root", Version: "1.0.0"}
 	rootCmd.AddCommand(&Command{Use: "sub", Run: emptyRun})

site/content/user_guide.md

@@ -596,6 +596,12 @@ Running an application with the '--version' flag will print the version to stdou
 the version template. The template can be customized using the
 `cmd.SetVersionTemplate(s string)` function.
 
+## Error Message Prefix
+
+Cobra prints an error message when being returned a non-nil error value.
+The default error message is `Error: error contents`.
+The Prefix, `Error:` can be customized using the `cmd.SetErrPrefix(s string)` function.
+
 ## PreRun and PostRun Hooks
 
 It is possible to run functions before or after the main `Run` function of your command. The `PersistentPreRun` and `PreRun` functions will be executed before `Run`. `PersistentPostRun` and `PostRun` will be executed after `Run`.  The `Persistent*Run` functions will be inherited by children if they do not declare their own.  These functions are run in the following order: