The Jargon File (version 4.4.7, 29 Dec 2003):

blurgle
 /bler'gl/, n.

    [UK] Spoken metasyntactic variable, to indicate some text that is obvious
    from context, or which is already known. If several words are to be
    replaced, blurgle may well be doubled or tripled. ?To look for something in
    several files use ?grep string blurgle blurgle?.? In each case, ?blurgle
    blurgle? would be understood to be replaced by the file you wished to
    search. Compare mumble, sense 7.


The Free On-line Dictionary of Computing (30 December 2018):

blurgle

   /bler'gl/ [Great Britain] Spoken metasyntactic variable, to
   indicate some text that is obvious from context, or which is
   already known.  If several words are to be replaced, blurgle
   may well be doubled or trebled.  "To look for something in
   several files use "grep string blurgle blurgle"."  In each
   case, "blurgle blurgle" would be understood to be replaced by
   the file you wished to search.  Compare mumble.

   [Jargon File]