feat(update): add self-update command

cmd/output/interactive_printer.go

@@ -104,6 +104,27 @@ func (p *interactivePrinter) Print(v any) error {
 		w("  git commit: %s\n", t.GitCommit)
 		w("  build date: %s\n", t.BuildDate)
 		w("  go:         %s %s %s\n", t.GoVersion, t.Compiler, t.Platform)
+	case UpdateResult:
+		switch t.Status {
+		case UpdateStatusUpToDate:
+			w("%s\n", styleGreen.Render("cloudctl is up to date ("+t.CurrentVersion+")."))
+		case UpdateStatusAvailable:
+			w("%s %s %s\n",
+				styleYellow.Render("A new version is available:"),
+				styleBold.Render(t.LatestVersion),
+				styleFaint.Render("(current: "+t.CurrentVersion+")"),
+			)
+			w("Run %s to install it.\n", styleBold.Render("cloudctl update"))
+		case UpdateStatusUpdated:
+			w("%s %s %s %s\n",
+				styleGreen.Render("cloudctl updated:"),
+				t.CurrentVersion,
+				styleGreen.Render("->"),
+				styleBold.Render(t.LatestVersion),
+			)
+		default:
+			w("cloudctl update status: %s (current: %s, latest: %s)\n", t.Status, t.CurrentVersion, t.LatestVersion)
+		}
 	default:
 		w("%v\n", v)
 	}

cmd/output/plain_printer.go

@@ -87,6 +87,19 @@ func (p *plainPrinter) Print(v any) error {
 		w("  build date: %s\n", t.BuildDate)
 		w("  go:         %s %s %s\n", t.GoVersion, t.Compiler, t.Platform)
 
+	case UpdateResult:
+		switch t.Status {
+		case UpdateStatusUpToDate:
+			w("cloudctl is up to date (%s).\n", t.CurrentVersion)
+		case UpdateStatusAvailable:
+			w("A new version is available: %s (current: %s)\n", t.LatestVersion, t.CurrentVersion)
+			w("Run `cloudctl update` to install it.\n")
+		case UpdateStatusUpdated:
+			w("cloudctl updated: %s -> %s\n", t.CurrentVersion, t.LatestVersion)
+		default:
+			w("cloudctl update status: %s (current: %s, latest: %s)\n", t.Status, t.CurrentVersion, t.LatestVersion)
+		}
+
 	default:
 		w("%v\n", v)
 	}

cmd/output/types.go

@@ -51,6 +51,22 @@ type ErrorResult struct {
 	Error string `json:"error" yaml:"error"`
 }
 
+// UpdateStatus represents the outcome of an update check or install.
+type UpdateStatus string
+
+const (
+	UpdateStatusUpToDate  UpdateStatus = "up-to-date"
+	UpdateStatusAvailable UpdateStatus = "available"
+	UpdateStatusUpdated   UpdateStatus = "updated"
+)
+
+// UpdateResult is the output of the update command.
+type UpdateResult struct {
+	CurrentVersion string       `json:"currentVersion" yaml:"currentVersion"`
+	LatestVersion  string       `json:"latestVersion"  yaml:"latestVersion"`
+	Status         UpdateStatus `json:"status"         yaml:"status"`
+}
+
 // AccessDiff describes one cluster access (context) that is changing.
 type AccessDiff struct {
 	Name       string        `json:"name"             yaml:"name"`

cmd/root.go

@@ -30,6 +30,7 @@ Commands:
   sync              Fetch ClusterKubeconfigs from Greenhouse and merge them locally
   cluster-version   Query the Kubernetes server version of a kubeconfig context
   version           Print cloudctl build information
+  update            Check for and install the latest cloudctl release
 
 Global flags available on every command:
   -o, --output text|json|yaml   Output format (default: text)
@@ -86,6 +87,7 @@ func init() {
 	rootCmd.AddCommand(syncCmd)
 	rootCmd.AddCommand(clusterVersionCmd)
 	rootCmd.AddCommand(versionCmd)
+	rootCmd.AddCommand(updateCmd)
 }
 
 // configWithContext builds a rest.Config for the specified context name from the given kubeconfig path.