Shell script changing desktop wallpaper

This is just my approach on this matter. I don't claim that it's the ideal one.

WALLS_PATH=/path/to/images
cd $WALLS_PATH

while [ 1 ]; do
    for NEW_WALL in "$WALLS_PATH"/*; do
        gsettings set org.gnome.desktop.background picture-uri "file://${NEW_WALL}"
        sleep 1800
    done
done

I know this answer is kind of late but since it could help some people, I'm posting it.

From septi's code plus some modifications, here is my solution :

#!/bin/bash
wallpaperdir="$HOME/wallpaper"

files=($wallpaperdir/*)
randompic=`printf "%s\n" "${files[RANDOM % ${#files[@]}]}"`

echo -e "# xfce backdrop list\n$randompic">$HOME/.config/xfce4/desktop/backdrop.list
xfdesktop --reload

The single quotes must be replaced by double quotes in order for the computer to interpret the $HOME part correctly. Also, the file you want to edit is backdrop.list, not backdrops.list. And finally, I find that using killall is kind of excessive in this case, since you can simply reload xfdesktop.

I've tested it on my computer (Linux Mint Debian Edition) and it seems to work perfectly.

Hope it helps. =)

EDIT : I forgot to mention that you have to add DISPLAY=:0.0 before your command, in crontab. That gives

*/1 * * * * DISPLAY=:0.0 wallpaper.sh

#!/bin/bash
wallpaperdir='$HOME/wallpaper'

files=($wallpaperdir/*)
randompic=`printf "%s\n" "${files[RANDOM % ${#files[@]}]}"`

gconftool-2 -t str --set /desktop/gnome/background/picture_filename "$randompic"

Save this script and edit your with the command "crontab -e" (it launches an editor where you put this line at the end of the file):

*/1     *     *     *     *         /bin/bash /path/to/script.sh

edit: I assumed you're using gnome. If not you need to edit the last line, because my example uses the Gnome Conftool. ;)

To change the background in XFCE, you should change the line with gconftool-2 to:

echo -e “# xfce backdrop list\n$randompic”>$HOME/.config/xfce4/desktop/backdrops.list    
killall -USR1 xfdesktop