Nitrogen wallpaper switcher: Dual Screen wallpaper via bash?

Question

I've grown quite attached to a little script for my laptop that lets me randomly switch the background with nitrogen:
#! /bin/bash
WALLPAPERS="/home/elias/Pics/BackgroundShow"
ALIST=( `ls -w1 $WALLPAPERS` )
RANGE=${#ALIST[@]}
let "number = $RANDOM"
let LASTNUM="`cat $WALLPAPERS/.last` + $number"
let "number = $LASTNUM % $RANGE"
echo $number > $WALLPAPERS/.last
nitrogen --set-zoom-fill --save $WALLPAPERS/${ALIST[$number]}           <---------- Just need to specify the screen here...
I've had no luck finding how to change just screen 1 or 2 without the GUI.  If there's a way, I would just have a separate hotkey for both.  man nitrogen and nitrogen --help say nothing about setting for a particular screen. 
Any help would be appreciated

Answer 1

I'm playing with imlibsetroot, but it doesn't appear to have the same "zoom-fill" function, and if you set one at a time, it clears the other screen.  So you can shuffle both with this:
#! /bin/bash
WALLPAPERS="/home/elias/Pics/BackShow"
ALIST=( `ls -w1 $WALLPAPERS` )
RANGE=${#ALIST[@]}
let "number = $RANDOM"
let LASTNUM="`cat $WALLPAPERS/.last` + $number"
let "number = $LASTNUM % $RANGE"
echo $number > $WALLPAPERS/.last
let "number2 = $RANDOM"
let LASTNUM="`cat $WALLPAPERS/.last` + $number2"
let "number2 = $LASTNUM % $RANGE"
echo $number2 > $WALLPAPERS/.last
imlibsetroot -x 0 -s $WALLPAPERS/${ALIST[$number]} -x 1 -s $WALLPAPERS/${ALIST[$number2]}
the option -s scales the image until it fills either the x or y dimension leaving black space.  Of course I could crop or limit myself to images with the right aspect ratio, but that's not a solution.  The options seem fairly extensive, but I don't see a way to emulate "zoom-fill":
usage: imlibsetroot [globalopts] {[screenopts] [imageopts] <filename>}+
global options
--help print usage information
--version print version information
--composite combine the images with the current root window
--display DDD connect to X display DDD
--store store the new root image to ~/.background.png
--store FILE store the new root image to FILE
--storeslices store the root image of each xinerama display
as a seperate file. (Implies --store .)
screen options
-x s operate on the single virtual xinerama screen
(default)
-x e operate on all xinerama screens independently
-x N operate on xinerama screen N
image options
-s scale pixmap to the current screen's size
preserving the pixmap's original aspect ratio
-s a scale pixmap to the current screen's size
preserving the pixmap's original aspect ratio
-s f scale pixmap to the current screen's size
without regard to the pixmap's original
aspect ratio
-s N scale pixmap by N percent
-s X,Y set the pixmap's width to X pixels and height
to Y pixels
-m {xy} mirror across the X/Y axis
-r {r|rr|l|ll} rotate right/left once or twice
-f {xy} flip the pixmap across the X/Y axis
-p c center pixmap on both axes
-p cx center pixmap on x
-p cy center pixmap on y
-p X,Y place pixmap at position X, Y on the current
screen (current screen based coordinates)
-t (integer tiling if combined with center
--bg COLOR set background color (the area not covered by the
image) to COLOR (COLOR may be a mnemonic, or a
RRR,GGG,BBB triple) (may be used without an image)
--bgcolor COLOR same as --bg