feat: flag action

app.go

@@ -342,6 +342,10 @@ func (a *App) RunContext(ctx context.Context, arguments []string) (err error) {
 		}
 	}
 
+	if err = runFlagActions(cCtx, a.Flags); err != nil {
+		return err
+	}
+
 	var c *Command
 	args := cCtx.Args()
 	if args.Present() {
@@ -523,6 +527,10 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 		}
 	}
 
+	if err = runFlagActions(cCtx, a.Flags); err != nil {
+		return err
+	}
+
 	args := cCtx.Args()
 	if args.Present() {
 		name := args.First()
@@ -646,6 +654,24 @@ func (a *App) argsWithDefaultCommand(oldArgs Args) Args {
 	return oldArgs
 }
 
+func runFlagActions(c *Context, fs []Flag) error {
+	for _, f := range fs {
+		isSet := false
+		for _, name := range f.Names() {
+			if c.IsSet(name) {
+				isSet = true
+				break
+			}
+		}
+		if isSet {
+			if err := f.RunAction(c); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 // Author represents someone who has contributed to a cli project.
 type Author struct {
 	Name  string // The Authors name