adding nicer help when missing arguments (#11858)

Signed-off-by: Jason Shepherd <jason@jasonshepherd.net>

api/client/cli.go

@@ -118,18 +118,21 @@ func (cli *DockerCli) Subcmd(name, signature, description string, exitOnError bo
 		errorHandling = flag.ContinueOnError
 	}
 	flags := flag.NewFlagSet(name, errorHandling)
+	if signature != "" {
+		signature = " " + signature
+	}
 	flags.Usage = func() {
+		flags.ShortUsage()
+		flags.PrintDefaults()
+		os.Exit(0)
+	}
+	flags.ShortUsage = func() {
 		options := ""
-		if signature != "" {
-			signature = " " + signature
-		}
 		if flags.FlagCountUndeprecated() > 0 {
 			options = " [OPTIONS]"
 		}
 		fmt.Fprintf(cli.out, "\nUsage: docker %s%s%s\n\n%s\n\n", name, options, signature, description)
 		flags.SetOutput(cli.out)
-		flags.PrintDefaults()
-		os.Exit(0)
 	}
 	return flags
 }

api/client/create.go

@@ -145,6 +145,7 @@ func (cli *DockerCli) CmdCreate(args ...string) error {
 	config, hostConfig, cmd, err := runconfig.Parse(cmd, args)
 	if err != nil {
 		cmd.ReportError(err.Error(), true)
+		os.Exit(1)
 	}
 	if config.Image == "" {
 		cmd.Usage()

api/client/run.go

@@ -57,6 +57,7 @@ func (cli *DockerCli) CmdRun(args ...string) error {
 	// just in case the Parse does not exit
 	if err != nil {
 		cmd.ReportError(err.Error(), true)
+		os.Exit(1)
 	}
 
 	if len(hostConfig.Dns) > 0 {

pkg/mflag/flag.go

@@ -289,7 +289,8 @@ type FlagSet struct {
 	// Usage is the function called when an error occurs while parsing flags.
 	// The field is a function (not a method) that may be changed to point to
 	// a custom error handler.
-	Usage func()
+	Usage      func()
+	ShortUsage func()
 
 	name             string
 	parsed           bool
@@ -564,6 +565,12 @@ var Usage = func() {
 	PrintDefaults()
 }
 
+// Usage prints to standard error a usage message documenting the standard command layout
+// The function is a variable that may be changed to point to a custom function.
+var ShortUsage = func() {
+	fmt.Fprintf(CommandLine.output, "Usage of %s:\n", os.Args[0])
+}
+
 // FlagCount returns the number of flags that have been defined.
 func (f *FlagSet) FlagCount() int { return len(sortFlags(f.formal)) }
 
@@ -1073,6 +1080,8 @@ func (cmd *FlagSet) ParseFlags(args []string, withHelp bool) error {
 	}
 	if str := cmd.CheckArgs(); str != "" {
 		cmd.ReportError(str, withHelp)
+		cmd.ShortUsage()
+		os.Exit(1)
 	}
 	return nil
 }
@@ -1085,8 +1094,7 @@ func (cmd *FlagSet) ReportError(str string, withHelp bool) {
 			str += ". See '" + os.Args[0] + " " + cmd.Name() + " --help'"
 		}
 	}
-	fmt.Fprintf(cmd.Out(), "docker: %s\n", str)
-	os.Exit(1)
+	fmt.Fprintf(cmd.Out(), "docker: %s.\n", str)
 }
 
 // Parsed reports whether f.Parse has been called.