bring Error: Command not found: <command>

Usage: docker COMMAND [arg...]

A self-sufficient runtime for linux containers.

Commands:
    attach    Attach to a running container
    insert    Insert a file in an image
    login     Register or Login to the docker registry server
    export    Stream the contents of a container as a tar archive
    diff      Inspect changes on a container's filesystem
    logs      Fetch the logs of a container
    pull      Pull an image or a repository from the docker registry server
    restart   Restart a running container
    build     Build a container from Dockerfile or via stdin
    history   Show the history of an image
    kill      Kill a running container
    rmi       Remove an image
    start     Start a stopped container
    tag       Tag an image into a repository
    commit    Create a new image from a container's changes
    import    Create a new filesystem image from the contents of a tarball
    ps        List containers
    rm        Remove a container
    run       Run a command in a new container
    wait      Block until a container stops, then print its exit code
    images    List images
    port      Lookup the public-facing port which is NAT-ed to PRIVATE_PORT
    info      Display system-wide information
    inspect   Return low-level information on a container
    push      Push an image or a repository to the docker registry server
    search    Search for an image in the docker index
    stop      Stop a running container
    version   Show the docker version information back

commands.go

@@ -30,15 +30,19 @@ var (
 	GIT_COMMIT string
 )
 
+func (cli *DockerCli) getMethod(name string) (reflect.Method, bool) {
+	methodName := "Cmd" + strings.ToUpper(name[:1]) + strings.ToLower(name[1:])
+	return reflect.TypeOf(cli).MethodByName(methodName)
+}
+
 func ParseCommands(args ...string) error {
 	cli := NewDockerCli("0.0.0.0", 4243)
 
 	if len(args) > 0 {
-		methodName := "Cmd" + strings.ToUpper(args[0][:1]) + strings.ToLower(args[0][1:])
-		method, exists := reflect.TypeOf(cli).MethodByName(methodName)
+		method, exists := cli.getMethod(args[0])
 		if !exists {
 			fmt.Println("Error: Command not found:", args[0])
-			return cli.CmdHelp(args...)
+			return cli.CmdHelp(args[1:]...)
 		}
 		ret := method.Func.CallSlice([]reflect.Value{
 			reflect.ValueOf(cli),
@@ -53,6 +57,18 @@ func ParseCommands(args ...string) error {
 }
 
 func (cli *DockerCli) CmdHelp(args ...string) error {
+	if len(args) > 0 {
+		method, exists := cli.getMethod(args[0])
+		if !exists {
+			fmt.Println("Error: Command not found:", args[0])
+		} else {
+			method.Func.CallSlice([]reflect.Value{
+				reflect.ValueOf(cli),
+				reflect.ValueOf([]string{"--help"}),
+			})[0].Interface()
+			return nil
+		}
+	}
 	help := "Usage: docker COMMAND [arg...]\n\nA self-sufficient runtime for linux containers.\n\nCommands:\n"
 	for cmd, description := range map[string]string{
 		"attach":  "Attach to a running container",