fix: permit empty string for ErrPrefix

command.go

@@ -193,6 +193,8 @@ type Command struct {
 
 	// errPrefix is the error message prefix defined by user.
 	errPrefix string
+	// errPrefixEmpty tracks if the user explicitly wants an empty errPrefix.
+	errPrefixEmpty bool
 
 	// inReader is a reader defined by the user that replaces stdin
 	inReader io.Reader
@@ -373,8 +375,19 @@ func (c *Command) SetVersionTemplate(s string) {
 }
 
 // SetErrPrefix sets error message prefix to be used. Application can use it to set custom prefix.
+// To unset the error prefix, this function should be called with the empty string.
+// To prevent an error prefix from being used, the function SetErrPrefixEmpty(true) should be used.
 func (c *Command) SetErrPrefix(s string) {
 	c.errPrefix = s
+	c.errPrefixEmpty = false
+}
+
+// SetErrPrefixEmpty sets whether the error message prefix should be empty.
+// If set to true, this suppresses the default "Error: " prefix.
+// To unset the error prefix (so the parent chain can be checked), please use SetErrPrefix("").
+func (c *Command) SetErrPrefixEmpty(empty bool) {
+	c.errPrefixEmpty = empty
+	c.errPrefix = ""
 }
 
 // SetGlobalNormalizationFunc sets a normalization function to all flag sets and also to child commands.
@@ -644,6 +657,9 @@ func (c *Command) ErrPrefix() string {
 	if c.errPrefix != "" {
 		return c.errPrefix
 	}
+	if c.errPrefixEmpty {
+		return ""
+	}
 
 	if c.HasParent() {
 		return c.parent.ErrPrefix()
@@ -1128,7 +1144,11 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 			c = cmd
 		}
 		if !c.SilenceErrors {
-			c.PrintErrln(c.ErrPrefix(), err.Error())
+			if errPrefix := c.ErrPrefix(); errPrefix != "" {
+				c.PrintErrln(errPrefix, err.Error())
+			} else {
+				c.PrintErrln(err.Error())
+			}
 			c.PrintErrf("Run '%v --help' for usage.\n", c.CommandPath())
 		}
 		return c, err
@@ -1157,7 +1177,11 @@ 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(cmd.ErrPrefix(), err.Error())
+			if errPrefix := cmd.ErrPrefix(); errPrefix != "" {
+				c.PrintErrln(errPrefix, err.Error())
+			} else {
+				c.PrintErrln(err.Error())
+			}
 		}
 
 		// If root command has SilenceUsage flagged,

command_test.go

@@ -1297,6 +1297,39 @@ func TestRootAndSubErrPrefix(t *testing.T) {
 	}
 }
 
+func TestRootErrPrefixEmpty(t *testing.T) {
+	rootCmd := &Command{Use: "root", Run: emptyRun}
+	rootCmd.SetErrPrefixEmpty(true)
+
+	output, err := executeCommand(rootCmd, "--unknown-root-flag")
+	if err == nil {
+		t.Errorf("Expected error")
+	}
+
+	checkStringOmits(t, output, "Error: ")
+	checkStringContains(t, output, "unknown flag: --unknown-root-flag")
+
+	// Ensure there is no leading space which used to happen with empty prefix
+	if strings.HasPrefix(output, " ") {
+		t.Errorf("Expected no leading space in error output, got %q", output)
+	}
+}
+
+func TestSetErrPrefixEmptyStringRestoresDefault(t *testing.T) {
+	rootCmd := &Command{Use: "root", Run: emptyRun}
+	rootCmd.SetErrPrefix("custom error:")
+
+	// Setting it to "" should restore the default "Error:" prefix for backward compatibility
+	rootCmd.SetErrPrefix("")
+
+	output, err := executeCommand(rootCmd, "--unknown-root-flag")
+	if err == nil {
+		t.Errorf("Expected error")
+	}
+
+	checkStringContains(t, output, "Error: unknown flag: --unknown-root-flag")
+}
+
 func TestVersionFlagExecutedOnSubcommand(t *testing.T) {
 	rootCmd := &Command{Use: "root", Version: "1.0.0"}
 	rootCmd.AddCommand(&Command{Use: "sub", Run: emptyRun})