main: print build version on startup

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"net/http"
 	"os"
 	"time"
@@ -22,10 +23,12 @@ Use "go2spec [command] --help" for more information about a command.
 
 If there are no commands provided, the tool will default to executing the 'pack' command.
 `
-	println(helpText)
+	fmt.Print(helpText)
 }
 
 func main() {
+	printVersion(os.Stdout)
+
 	pkgsiteHTTPClient = &http.Client{
 		Timeout:   30 * time.Second,
 		Transport: httpcache.NewMemoryCacheTransport(),
@@ -43,12 +46,12 @@ func main() {
 		printHelp()
 	case "pack":
 		// Placeholder for the pack command implementation
-		println("Executing 'pack' command...")
+		fmt.Println("Executing 'pack' command...")
 		// Actual packing logic would go here
 		mainPack(args[1:], nil)
 	default:
 		// Default to 'pack' command if no command is provided
-		println("No command provided. Defaulting to 'pack' command...")
+		fmt.Println("No command provided. Defaulting to 'pack' command...")
 		// Actual packing logic would go here
 		mainPack(args, printHelp)
 	}

version.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"runtime/debug"
+	"time"
+)
+
+const unknownVersion = "unknown"
+
+func runtimeVersion() string {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return unknownVersion
+	}
+	return versionFromBuildSettings(info.Settings)
+}
+
+func versionFromBuildSettings(settings []debug.BuildSetting) string {
+	var revision string
+	var commitTime string
+	for _, setting := range settings {
+		switch setting.Key {
+		case "vcs.revision":
+			revision = setting.Value
+		case "vcs.time":
+			commitTime = setting.Value
+		}
+	}
+	if revision == "" || commitTime == "" {
+		return unknownVersion
+	}
+	if len(revision) > 7 {
+		revision = revision[:7]
+	}
+	if t, err := time.Parse(time.RFC3339, commitTime); err == nil {
+		commitTime = t.Format("2006-01-02")
+	}
+	return fmt.Sprintf("%s %s", commitTime, revision)
+}
+
+func printVersion(w io.Writer) {
+	fmt.Fprintf(w, "Version: %s\n", runtimeVersion())
+}

version_test.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"runtime/debug"
+	"testing"
+)
+
+func TestVersionFromBuildSettings(t *testing.T) {
+	settings := []debug.BuildSetting{
+		{Key: "vcs.revision", Value: "1234567890abcdef"},
+		{Key: "vcs.time", Value: "2026-06-27T15:33:29Z"},
+	}
+
+	if got, want := versionFromBuildSettings(settings), "2026-06-27 1234567"; got != want {
+		t.Fatalf("versionFromBuildSettings() = %q, want %q", got, want)
+	}
+}
+
+func TestVersionFromBuildSettingsUnknown(t *testing.T) {
+	if got := versionFromBuildSettings(nil); got != unknownVersion {
+		t.Fatalf("versionFromBuildSettings(nil) = %q, want %q", got, unknownVersion)
+	}
+}