@@ -9,6 +9,7 @@ import (

 	"os"

 	"path/filepath"

 	"runtime"

+	"sort"

 	"strings"

 )

@@ -29,6 +30,10 @@ func Register(name string, handler Handler) error {

 	return nil

 }

+func unregister(name string) {

+	delete(globalHandlers, name)

+}

+

 // The Engine is the core of Docker.

 // It acts as a store for *containers*, and allows manipulation of these

 // containers by executing *jobs*.

@@ -106,6 +111,12 @@ func New(root string) (*Engine, error) {

 		Stderr:   os.Stderr,

 		Stdin:    os.Stdin,

 	}

+	eng.Register("commands", func(job *Job) Status {

+		for _, name := range eng.commands() {

+			job.Printf("%s\n", name)

+		}

+		return StatusOK

+	})

 	// Copy existing global handlers

 	for k, v := range globalHandlers {

 		eng.handlers[k] = v

@@ -117,6 +128,17 @@ func (eng *Engine) String() string {

 	return fmt.Sprintf("%s|%s", eng.Root(), eng.id[:8])

 }

+// Commands returns a list of all currently registered commands,

+// sorted alphabetically.

+func (eng *Engine) commands() []string {

+	names := make([]string, 0, len(eng.handlers))

+	for name := range eng.handlers {

+		names = append(names, name)

+	}

+	sort.Strings(names)

+	return names

+}

+

 // Job creates a new job which can later be executed.

 // This function mimics `Command` from the standard os/exec package.

 func (eng *Engine) Job(name string, args ...string) *Job {

@@ -1,6 +1,7 @@

 package engine

 import (

+	"bytes"

 	"io/ioutil"

 	"os"

 	"path"

@@ -17,6 +18,8 @@ func TestRegister(t *testing.T) {

 	if err := Register("dummy1", nil); err == nil {

 		t.Fatalf("Expecting error, got none")

 	}

+	// Register is global so let's cleanup to avoid conflicts

+	defer unregister("dummy1")

 	eng := newTestEngine(t)

@@ -33,6 +36,7 @@ func TestRegister(t *testing.T) {

 	if err := eng.Register("dummy2", nil); err == nil {

 		t.Fatalf("Expecting error, got none")

 	}

+	defer unregister("dummy2")

 }

 func TestJob(t *testing.T) {

@@ -49,6 +53,7 @@ func TestJob(t *testing.T) {

 	}

 	eng.Register("dummy2", h)

+	defer unregister("dummy2")

 	job2 := eng.Job("dummy2", "--level=awesome")

 	if job2.handler == nil {

@@ -60,6 +65,24 @@ func TestJob(t *testing.T) {

 	}

 }

+func TestEngineCommands(t *testing.T) {

+	eng := newTestEngine(t)

+	defer os.RemoveAll(eng.Root())

+	handler := func(job *Job) Status { return StatusOK }

+	eng.Register("foo", handler)

+	eng.Register("bar", handler)

+	eng.Register("echo", handler)

+	eng.Register("die", handler)

+	var output bytes.Buffer

+	commands := eng.Job("commands")

+	commands.Stdout.Add(&output)

+	commands.Run()

+	expected := "bar\ncommands\ndie\necho\nfoo\n"

+	if result := output.String(); result != expected {

+		t.Fatalf("Unexpected output:\nExpected = %v\nResult   = %v\n", expected, result)

+	}

+}

+

 func TestEngineRoot(t *testing.T) {

 	tmp, err := ioutil.TempDir("", "docker-test-TestEngineCreateDir")

 	if err != nil {