org-babel-tangle: now careful to only add one shebang per file

contrib/babel/lisp/org-babel-tangle.el

@@ -88,7 +88,8 @@ exported source code blocks by language."
                 (lang-specs (cdr (assoc lang org-babel-tangle-langs)))
                 (ext (first lang-specs))
                 (she-bang (second lang-specs))
-                (commentable (not (third lang-specs))))
+                (commentable (not (third lang-specs)))
+                she-banged)
            (mapc
             (lambda (spec)
               (let* ((tangle (cdr (assoc :tangle (third spec))))
@@ -113,7 +114,9 @@ exported source code blocks by language."
                   ;; drop source-block to file
                   (with-temp-buffer
                     (funcall lang-f)
-                    (when she-bang (insert (concat she-bang "\n")))
+                    (when (and she-bang (not (member file-name she-banged)))
+                      (insert (concat she-bang "\n"))
+                      (setq she-banged (cons file-name she-banged)))
                     (when commentable
                       (comment-region
                        (point) (progn (insert "generated by org-babel-tangle") (point)))