Multi-monitor background splitter and setter

multi-bg-set.sh

#!/bin/bash
# Easy to use!
# awsetbg -u /path/to/multi-bg-set.sh -r /path/to/images
# Or, just call it by itself: /path/to/multi-bg-set.sh /path/to/some/image.ext

INPUT=$1
if [ ! -f "$INPUT" ]
	then
	echo "Input file must exist!"
	exit 1
	fi

# Can we use the md5sum caching?
if md5sum --version &> /dev/null
	then
	# Checking to see if there's already a complete split image ready
	MD5=$(md5sum "$INPUT" 2>/dev/null | cut -f1 -d\ )
	if [ ! -f "/tmp/wallpaper-$MD5-0.jpg" -o \
		 ! -f "/tmp/wallpaper-$MD5-1.jpg" -o \
		 ! -f "/tmp/wallpaper-$MD5-2.jpg" -o \
		 ! -f "/tmp/wallpaper-$MD5-3.jpg" ]
		then
		# No file yet, or incomplete cache, so we'll build a new set.
		nice -n 19 convert -crop 50%x50% +repage "$INPUT" /tmp/wallpaper-$MD5.jpg
		fi
	DISPLAY=:0.0 feh --bg-scale /tmp/wallpaper-$MD5-1.jpg &
	DISPLAY=:0.1 feh --bg-scale /tmp/wallpaper-$MD5-3.jpg &
	DISPLAY=:0.2 feh --bg-scale /tmp/wallpaper-$MD5-2.jpg &
	DISPLAY=:0.3 feh --bg-scale /tmp/wallpaper-$MD5-0.jpg
	
# Nope, cannot use cached copies, do it all from scratch
	else
	nice -n 19 convert -crop 50%x50% +repage "$INPUT" /tmp/wallpaper.jpg
	DISPLAY=:0.0 feh --bg-scale /tmp/wallpaper-1.jpg &
	DISPLAY=:0.1 feh --bg-scale /tmp/wallpaper-3.jpg &
	DISPLAY=:0.2 feh --bg-scale /tmp/wallpaper-2.jpg &
	DISPLAY=:0.3 feh --bg-scale /tmp/wallpaper-0.jpg
	fi

Just a quick note:
I wrote this to split a 3840x2160 image into 4 pieces, one for each 1920x1080 display (2x2 configuration), and apply them (using "feh")

Now with "caching"! No longer re-converts an image every single time. Instead, it checks for a cached set in /tmp/.