xfce-set-backdrop.sh

#!/bin/sh                                                                        
[ -z "$1" ] && echo "Usage: $0 path" && exit 0;                                  
[ ! -f "$1" ] && echo "File not found: $1" && exit 1;                            
                                                                                 
img=$(realpath $1);                                                              
xfconf_query="/usr/bin/xfconf-query";                                            
                                                                                 
query() {                                                                        
    $xfconf_query -c xfce4-desktop -l | grep '^/backdrop/.*/last-image' || echo "fail" && exit 1
}                                                                                
query | while read p; do                                                         
    $xfconf_query -c xfce4-desktop -p $p --set "$img";                           
done