show version with branch and commit in help and -version

- add -version flag (besides --version and -V)
- help output includes the version
- commit and branch are set via ldflags by goreleaser; plain go build
  falls back to the VCS revision embedded by Go

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main.go

@@ -9,6 +9,7 @@ import (
 	"os/signal"
 	"os/user"
 	"path/filepath"
+	"runtime/debug"
 	"strings"
 	"unicode"
 	"unicode/utf8"
@@ -19,8 +20,51 @@ import (
 // ErrNoPath is returned when 'cd' was called without a second argument.
 var ErrNoPath = errors.New("path required")
 
-// version is set at build time via -ldflags "-X main.version=..."
-var version = "dev"
+// Build information, set at build time via
+// -ldflags "-X main.version=... -X main.commit=... -X main.branch=...".
+var (
+	version = "dev"
+	commit  = ""
+	branch  = ""
+)
+
+// versionInfo returns the version including branch and commit, e.g.
+// "0.2.1 (branch: main, commit: 03e791c)". Without ldflags (plain go build)
+// the commit is taken from the VCS information that Go embeds in the binary.
+func versionInfo() string {
+	c := commit
+	if c == "" {
+		if info, ok := debug.ReadBuildInfo(); ok {
+			var dirty bool
+			for _, s := range info.Settings {
+				switch s.Key {
+				case "vcs.revision":
+					c = s.Value
+				case "vcs.modified":
+					dirty = s.Value == "true"
+				}
+			}
+			if len(c) > 7 {
+				c = c[:7]
+			}
+			if c != "" && dirty {
+				c += "-dirty"
+			}
+		}
+	}
+
+	var details []string
+	if branch != "" {
+		details = append(details, "branch: "+branch)
+	}
+	if c != "" {
+		details = append(details, "commit: "+c)
+	}
+	if len(details) == 0 {
+		return version
+	}
+	return version + " (" + strings.Join(details, ", ") + ")"
+}
 
 // previousDir tracks the previous working directory for 'cd -' support
 var previousDir string
@@ -568,9 +612,12 @@ func completeFilePath(line, prefix string) []string {
 }
 
 func main() {
-	if len(os.Args) > 1 && (os.Args[1] == "--version" || os.Args[1] == "-V") {
-		fmt.Println("gosh", version)
-		return
+	if len(os.Args) > 1 {
+		switch os.Args[1] {
+		case "-version", "--version", "-V":
+			fmt.Println("gosh", versionInfo())
+			return
+		}
 	}
 
 	// Ctrl+C sends SIGINT to the whole foreground process group. Catch it so
@@ -727,7 +774,7 @@ func execInput(input string) error {
 		os.Setenv(parts[0], parts[1])
 		return nil
 	case "help":
-		fmt.Println(`gosh - Go Shell
+		fmt.Println("gosh - Go Shell\nVersion: " + versionInfo() + `
 
 Built-in commands:
   cd [dir]       - Change directory (cd with no args goes to home)