/usr/share/gimp/2.0/scripts/difference-clouds.scm is in gimp-data 2.8.10-0ubuntu1.2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 | ; Plugin for the GNU Image Manipulation Program
; Copyright (C) 2006 Martin Nordholts
;
; This program is free software: you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 3 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program.  If not, see <http://www.gnu.org/licenses/>.
;
; Renders Difference Clouds onto a layer, i.e. solid noise merged down with the
; Difference Mode
;
(define (script-fu-difference-clouds image
                                     drawable)
  (let* ((draw-offset-x (car (gimp-drawable-offsets drawable)))
         (draw-offset-y (cadr (gimp-drawable-offsets drawable)))
         (has-sel       (car (gimp-drawable-mask-intersect drawable)))
         (sel-offset-x  (cadr (gimp-drawable-mask-intersect drawable)))
         (sel-offset-y  (caddr (gimp-drawable-mask-intersect drawable)))
         (width         (cadddr (gimp-drawable-mask-intersect drawable)))
         (height        (caddr (cddr (gimp-drawable-mask-intersect drawable))))
         (type          (car (gimp-drawable-type-with-alpha drawable)))
         (diff-clouds   (car (gimp-layer-new image width height type
                                             "Clouds" 100 DIFFERENCE-MODE)))
         (offset-x      0)
         (offset-y      0)
        )
    (gimp-image-undo-group-start image)
    ; Add the cloud layer above the current layer
    (gimp-image-insert-layer image diff-clouds 0 -1)
    ; Clear the layer (so there are no noise in it)
    (gimp-drawable-fill diff-clouds TRANSPARENT-FILL)
    ; Selections are relative to the drawable; adjust the final offset
    (set! offset-x (+ draw-offset-x sel-offset-x))
    (set! offset-y (+ draw-offset-y sel-offset-y))
    ; Offset the clouds layer
    (if (gimp-item-is-layer drawable)
      (gimp-layer-translate diff-clouds offset-x offset-y))
    ; Show the solid noise dialog
    (plug-in-solid-noise SF-RUN-MODE image diff-clouds 0 0 0 1 4.0 4.0)
    ; Merge the clouds layer with the layer below
    (gimp-image-merge-down image diff-clouds EXPAND-AS-NECESSARY)
    (gimp-image-undo-group-end image)
    (gimp-displays-flush)
  )
)
(script-fu-register "script-fu-difference-clouds"
                    _"Difference Clouds..."
                    _"Solid noise applied with Difference layer mode"
                    "Martin Nordholts <enselic@hotmail.com>"
                    "Martin Nordholts"
                    "2006/10/25"
                    "RGB* GRAY*"
                    SF-IMAGE       "Image"           0
                    SF-DRAWABLE    "Drawable"        0)
(script-fu-menu-register "script-fu-difference-clouds"
			 "<Image>/Filters/Render/Clouds")
 |