Required flags

app.go

@@ -116,19 +116,30 @@ func (a *App) Run(arguments []string) (err error) {
 	set.SetOutput(ioutil.Discard)
 	err = set.Parse(arguments[1:])
 	nerr := normalizeFlags(a.Flags, set)
-	if nerr != nil {
-		fmt.Fprintln(a.Writer, nerr)
-		context := NewContext(a, set, set)
+	cerr := checkRequiredFlags(a.Flags, set)
+
+	context := NewContext(a, set, set)
+
+	// Define here so it closes over the above variables
+	showErrAndHelp := func(err error) {
+		fmt.Fprintln(a.Writer, err)
+		fmt.Fprintln(a.Writer)
 		ShowAppHelp(context)
 		fmt.Fprintln(a.Writer)
+	}
+
+	if nerr != nil {
+		showErrAndHelp(nerr)
 		return nerr
 	}
-	context := NewContext(a, set, set)
+
+	if cerr != nil {
+		showErrAndHelp(cerr)
+		return cerr
+	}
 
 	if err != nil {
-		fmt.Fprintf(a.Writer, "Incorrect Usage.\n\n")
-		ShowAppHelp(context)
-		fmt.Fprintln(a.Writer)
+		showErrAndHelp(fmt.Errorf("Incorrect Usage."))
 		return err
 	}
 
@@ -204,22 +215,34 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 	set.SetOutput(ioutil.Discard)
 	err = set.Parse(ctx.Args().Tail())
 	nerr := normalizeFlags(a.Flags, set)
+	cerr := checkRequiredFlags(a.Flags, set)
+
 	context := NewContext(a, set, ctx.globalSet)
 
-	if nerr != nil {
-		fmt.Fprintln(a.Writer, nerr)
+	// Define here so it closes over the above variables
+	showErrAndHelp := func(err error) {
+		fmt.Fprintln(a.Writer, err)
+		fmt.Fprintln(a.Writer)
 		if len(a.Commands) > 0 {
 			ShowSubcommandHelp(context)
 		} else {
 			ShowCommandHelp(ctx, context.Args().First())
 		}
-		fmt.Fprintln(a.Writer)
+		fmt.Fprintln(a.Writer, err)
+	}
+
+	if nerr != nil {
+		showErrAndHelp(nerr)
 		return nerr
 	}
 
+	if cerr != nil {
+		showErrAndHelp(cerr)
+		return cerr
+	}
+
 	if err != nil {
-		fmt.Fprintf(a.Writer, "Incorrect Usage.\n\n")
-		ShowSubcommandHelp(context)
+		showErrAndHelp(err)
 		return err
 	}
 

command.go

@@ -88,21 +88,31 @@ func (c Command) Run(ctx *Context) error {
 		err = set.Parse(ctx.Args().Tail())
 	}
 
-	if err != nil {
-		fmt.Fprint(ctx.App.Writer, "Incorrect Usage.\n\n")
+	// Define here so it closes over the above variables
+	showErrAndHelp := func(err error) {
+		fmt.Fprintln(ctx.App.Writer, err)
+		fmt.Fprintln(ctx.App.Writer)
 		ShowCommandHelp(ctx, c.Name)
 		fmt.Fprintln(ctx.App.Writer)
+	}
+
+	if err != nil {
+		showErrAndHelp(fmt.Errorf("Incorrect Usage."))
 		return err
 	}
 
 	nerr := normalizeFlags(c.Flags, set)
 	if nerr != nil {
-		fmt.Fprintln(ctx.App.Writer, nerr)
-		fmt.Fprintln(ctx.App.Writer)
-		ShowCommandHelp(ctx, c.Name)
-		fmt.Fprintln(ctx.App.Writer)
+		showErrAndHelp(nerr)
 		return nerr
 	}
+
+	cerr := checkRequiredFlags(c.Flags, set)
+	if cerr != nil {
+		showErrAndHelp(cerr)
+		return cerr
+	}
+
 	context := NewContext(ctx.App, set, ctx.globalSet)
 
 	if checkCommandCompletions(context, c.Name) {
@@ -156,5 +166,8 @@ func (c Command) startApp(ctx *Context) error {
 		app.Action = helpSubcommand.Action
 	}
 
+	// set the writer to the original App's writer
+	app.Writer = ctx.App.Writer
+
 	return app.RunAsSubcommand(ctx)
 }

context.go

@@ -3,6 +3,7 @@ package cli
 import (
 	"errors"
 	"flag"
+	"fmt"
 	"strconv"
 	"strings"
 	"time"
@@ -337,3 +338,27 @@ func normalizeFlags(flags []Flag, set *flag.FlagSet) error {
 	}
 	return nil
 }
+
+func checkRequiredFlags(flags []Flag, set *flag.FlagSet) error {
+	// If the help flag is included then none of the other flags are required.
+	for _, f := range flags {
+		if f.getName() == "help" {
+			return nil
+		}
+	}
+
+	visited := make(map[string]bool)
+	set.Visit(func(f *flag.Flag) {
+		visited[f.Name] = true
+	})
+
+	for _, f := range flags {
+		if f.IsRequired() {
+			key := strings.Split(f.getName(), ",")[0]
+			if !visited[key] {
+				return fmt.Errorf("Required flag %s not set", f.getName())
+			}
+		}
+	}
+	return nil
+}