Change destop background in gnome 3

Backround.sh

BACKGROUND_PATH="/home/denis/Pictures/AT_wallpapers/"
BACKGROUND_STYLE="scaled" ## 'zoom', 'tiled', 'scaled', 'stretched', 'centered'
CYCLE_TIME="300"
TEMP_LOG="/tmp/rotate${RANDOM}.log"
LOG="/tmp/.`whoami`-gnome-background-rotator"
 
##Write Date & Time to Log File
echo "-------------------------------------" > "${LOG}"
echo "`date +\%B\ \%d,\ \%Y`" >> "${LOG}"
echo "-------------------------------------" >> "${LOG}"
 
USAGE="Usage: ${0} -p <SOURCE_DIRECTORY> -t <CYCLE_TIME> -k <KEYWORD>"
 
echo "Gnome Background Rotator"

echo
 
while getopts ':p:k:t:h' OPTION; do
  case ${OPTION} in
		p) BGPATH="${OPTARG}";;
		k) KEYWORD="${OPTARG}";;
		t) CTIME="${OPTARG}";;
		h) echo "${USAGE}" >&2
			exit 2;;
		\?) echo "Unknown option \"-${OPTARG}\"." >&2
			echo ${USAGE};;
		:) echo "Option \"-${OPTARG}\" needs an argument." >&2
  			echo ${USAGE}
  			exit 2;;
  		*) echo ${USAGE}
  			exit 2;;
  	esac
done
 
if [ "$BGPATH" ] #Check to see if another background source was given.
then
	if [ -d "$BGPATH" ]
	then
		BACKGROUND_PATH="${BGPATH}"
	else
		echo "Unable to continue.  Source specified is not a (readable) directory."
		exit
	fi
fi
 
if [ "$CTIME" ] #Check to see if another cycle time was given.
then
	if [ "$CTIME" -gt 0 ]
	then
		CYCLE_TIME="${CTIME}"
	else
		echo "Unable to continue.  Time given is not a valid number."
		exit
	fi
fi
 
gsettings set org.gnome.desktop.background picture-options ${BACKGROUND_STYLE}
 
#Search for images and create a temporary logfile of all matches
if [ "$KEYWORD" ]
then
	find ${BACKGROUND_PATH} -iname "*${KEYWORD}*.jpg" -or -iname "*${KEYWORD}*.png" -or -iname "*${KEYWORD}*.svg" > ${TEMP_LOG}
else
	find ${BACKGROUND_PATH} -iname "*.jpg" -or -iname "*.png" -or -iname "*.svg" > ${TEMP_LOG}
fi
 
LowerBound=1
RandomMax=32767
UpperBound=$(cat ${TEMP_LOG} | wc -l)
 
if [ $UpperBound -gt 0 ] #Check to make sure 1 or more results have been returned.
then
	echo "Starting to rotate through ${UpperBound} images(s)."
else
	echo "No images found.  Please change directories, or try another keyword."
	exit
fi
 
while [ "true" ]
	do
		# Choose a random line number (any number from 1 to the length of the file)
		RandomLine=$(( ${LowerBound} + (${UpperBound} * ${RANDOM}) / (${RandomMax} + 1) ))
 
		# Use sed to grab the random line
		IMAGE=$(sed -n "$RandomLine{p;q;}" "${TEMP_LOG}")
 
		if [ -r $IMAGE ]
		then	
        		echo "Changing background to: ${IMAGE}"
        		gsettings set org.gnome.desktop.background picture-uri file:///"${IMAGE}"
        		sleep ${CYCLE_TIME}
        	else
        		echo "Unable to change the background to: ${IMAGE}"
        		echo "The background either does not exist anymore, or the permissions to it are denied."
        	fi
	done
done