#!/bin/bash

BGSAVED=/home/<user>/.config/nitrogen/bg-saved.cfg
WALLPAPERS=/home/<user>/Pictures/wallpapers/
MODE=4

export DISPLAY=:0

FILENAME="$(ls ${WALLPAPERS} | shuf -n 1)"

echo '[xin_0]' > ${BGSAVED}
echo "file=${WALLPAPERS}/${FILENAME}" >> ${BGSAVED}
echo "mode=${MODE}" >> ${BGSAVED}
echo 'bgcolor=#000000' >> ${BGSAVED}

/usr/bin/nitrogen --restore
# or just 
# nitrogen --restore