Allow custom ExitError handler function

app.go

@@ -83,6 +83,9 @@ type App struct {
 	Writer io.Writer
 	// ErrWriter writes error output
 	ErrWriter io.Writer
+	// Execute this function to handle ExitErrors. If not provided, HandleExitCoder is provided to
+	// function as a default, so this is optional.
+	ExitErrHandler ExitErrHandlerFunc
 	// Other custom info
 	Metadata map[string]interface{}
 	// Carries a function which returns app specific info.
@@ -207,7 +210,7 @@ func (a *App) Run(arguments []string) (err error) {
 	if err != nil {
 		if a.OnUsageError != nil {
 			err := a.OnUsageError(context, err, false)
-			HandleExitCoder(err)
+			a.handleExitCoder(context, err)
 			return err
 		}
 		fmt.Fprintf(a.Writer, "%s %s\n\n", "Incorrect Usage.", err.Error())
@@ -240,8 +243,9 @@ func (a *App) Run(arguments []string) (err error) {
 	if a.Before != nil {
 		beforeErr := a.Before(context)
 		if beforeErr != nil {
+			fmt.Fprintf(a.Writer, "%v\n\n", beforeErr)
 			ShowAppHelp(context)
-			HandleExitCoder(beforeErr)
+			a.handleExitCoder(context, beforeErr)
 			err = beforeErr
 			return err
 		}
@@ -263,7 +267,7 @@ func (a *App) Run(arguments []string) (err error) {
 	// Run default Action
 	err = HandleAction(a.Action, context)
 
-	HandleExitCoder(err)
+	a.handleExitCoder(context, err)
 	return err
 }
 
@@ -330,7 +334,7 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 	if err != nil {
 		if a.OnUsageError != nil {
 			err = a.OnUsageError(context, err, true)
-			HandleExitCoder(err)
+			a.handleExitCoder(context, err)
 			return err
 		}
 		fmt.Fprintf(a.Writer, "%s %s\n\n", "Incorrect Usage.", err.Error())
@@ -352,7 +356,7 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 		defer func() {
 			afterErr := a.After(context)
 			if afterErr != nil {
-				HandleExitCoder(err)
+				a.handleExitCoder(context, err)
 				if err != nil {
 					err = NewMultiError(err, afterErr)
 				} else {
@@ -365,7 +369,7 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 	if a.Before != nil {
 		beforeErr := a.Before(context)
 		if beforeErr != nil {
-			HandleExitCoder(beforeErr)
+			a.handleExitCoder(context, beforeErr)
 			err = beforeErr
 			return err
 		}
@@ -383,7 +387,7 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 	// Run default Action
 	err = HandleAction(a.Action, context)
 
-	HandleExitCoder(err)
+	a.handleExitCoder(context, err)
 	return err
 }
 
@@ -464,6 +468,14 @@ func (a *App) appendFlag(flag Flag) {
 	}
 }
 
+func (a *App) handleExitCoder(context *Context, err error) {
+	if a.ExitErrHandler != nil {
+		a.ExitErrHandler(context, err)
+	} else {
+		HandleExitCoder(err)
+	}
+}
+
 // Author represents someone who has contributed to a cli project.
 type Author struct {
 	Name  string // The Authors name

app_test.go

@@ -1658,6 +1658,42 @@ func TestHandleAction_WithInvalidFuncReturnSignature(t *testing.T) {
 	}
 }
 
+func TestHandleExitCoder_Default(t *testing.T) {
+	app := NewApp()
+	fs, err := flagSet(app.Name, app.Flags)
+	if err != nil {
+		t.Errorf("error creating FlagSet: %s", err)
+	}
+
+	ctx := NewContext(app, fs, nil)
+	app.handleExitCoder(ctx, NewExitError("Default Behavior Error", 42))
+
+	output := fakeErrWriter.String()
+	if !strings.Contains(output, "Default") {
+		t.Fatalf("Expected Default Behavior from Error Handler but got: %s", output)
+	}
+}
+
+func TestHandleExitCoder_Custom(t *testing.T) {
+	app := NewApp()
+	fs, err := flagSet(app.Name, app.Flags)
+	if err != nil {
+		t.Errorf("error creating FlagSet: %s", err)
+	}
+
+	app.ExitErrHandler = func(_ *Context, _ error) {
+		fmt.Fprintln(ErrWriter, "I'm a Custom error handler, I print what I want!")
+	}
+
+	ctx := NewContext(app, fs, nil)
+	app.handleExitCoder(ctx, NewExitError("Default Behavior Error", 42))
+
+	output := fakeErrWriter.String()
+	if !strings.Contains(output, "Custom") {
+		t.Fatalf("Expected Custom Behavior from Error Handler but got: %s", output)
+	}
+}
+
 func TestHandleAction_WithUnknownPanic(t *testing.T) {
 	defer func() { refute(t, recover(), nil) }()
 

command.go

@@ -167,7 +167,7 @@ func (c Command) Run(ctx *Context) (err error) {
 	if err != nil {
 		if c.OnUsageError != nil {
 			err := c.OnUsageError(context, err, false)
-			HandleExitCoder(err)
+			context.App.handleExitCoder(context, err)
 			return err
 		}
 		fmt.Fprintln(context.App.Writer, "Incorrect Usage:", err.Error())
@@ -184,7 +184,7 @@ func (c Command) Run(ctx *Context) (err error) {
 		defer func() {
 			afterErr := c.After(context)
 			if afterErr != nil {
-				HandleExitCoder(err)
+				context.App.handleExitCoder(context, err)
 				if err != nil {
 					err = NewMultiError(err, afterErr)
 				} else {
@@ -198,7 +198,7 @@ func (c Command) Run(ctx *Context) (err error) {
 		err = c.Before(context)
 		if err != nil {
 			ShowCommandHelp(context, c.Name)
-			HandleExitCoder(err)
+			context.App.handleExitCoder(context, err)
 			return err
 		}
 	}
@@ -210,7 +210,7 @@ func (c Command) Run(ctx *Context) (err error) {
 	err = HandleAction(c.Action, context)
 
 	if err != nil {
-		HandleExitCoder(err)
+		context.App.handleExitCoder(context, err)
 	}
 	return err
 }

funcs.go

@@ -23,6 +23,10 @@ type CommandNotFoundFunc func(*Context, string)
 // is displayed and the execution is interrupted.
 type OnUsageErrorFunc func(context *Context, err error, isSubcommand bool) error
 
+// ExitErrHandlerFunc is executed if provided in order to handle ExitError values
+// returned by Actions and Before/After functions.
+type ExitErrHandlerFunc func(context *Context, err error)
+
 // FlagStringFunc is used by the help generation to display a flag, which is
 // expected to be a single line.
 type FlagStringFunc func(Flag) string
@@ -34,3 +38,4 @@ type FlagNamePrefixFunc func(fullName, placeholder string) string
 // FlagEnvHintFunc is used by the default FlagStringFunc to annotate flag help
 // with the environment variable details.
 type FlagEnvHintFunc func(envVar, str string) string
+