Add version command

cmd/sing-box/cmd_version.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"os"
+	"runtime"
+
+	C "github.com/sagernet/sing-box/constant"
+	F "github.com/sagernet/sing/common/format"
+	"github.com/spf13/cobra"
+)
+
+var commandVersion = &cobra.Command{
+	Use:   "version",
+	Short: "Print current version of sing-box",
+	Run:   printVersion,
+}
+
+func printVersion(cmd *cobra.Command, args []string) {
+	os.Stderr.WriteString(F.ToString("sing-box version ", C.Version, " (", runtime.Version(), " ", runtime.GOOS, "/", runtime.GOARCH, ")\n"))
+}