try filetype

main.go

@@ -12,6 +12,7 @@ import (
   "regexp"
   "strings"
   "syscall"
+  "github.com/h2non/filetype"
   "golang.org/x/crypto/ssh/terminal"
 )
 
@@ -130,6 +131,10 @@ func main() {
   FileName = readFn()
   fn := FileName
   fmt.Println(fn)
+  data := file2data(fn)
+  fType, _ := filetype.Get(data)
+  fmt.Println(fType.Extension)
+  os.Exit(0)
   mode := getMode()
   switch mode {
     case "h":