Gnome background changer

Wednesday, 16 June 2010

Gnome 2.3 on Ubuntu 10.04 LTS (Lucid Lynx) doesn’t appear to have an automatic wallpaper changer built in. While it appears there are many ways to accomplish this, I decided to write my own little script to get some time in with bash… alternative ways I have found include using Wallpaper-tray (which doesn’t appear to be in 10.04), Desktop Drapes, or a variation of the script below using things like gconftool-2.

To use this script, do the following:

Right-click on the desktop and choose Change Desktop Background
Look through the backgrounds, and make sure the ones listed are the ones you want to have the script randomly select

Open up a text file using gedit, and add the contents of the script:

#!/usr/bin/env bash
installedDir=~/Pictures/backgrounds/random
i=0
while read line; do
    data=`echo "${line}" | grep -i filename`
    if [ "$data" != "" ]; then
      filenameCutLength=$((${#data}-11))
      filename=$(echo $data | cut -b11-$filenameCutLength)
      if [ "$filename" != "(none)" ] \
        || [ "$filename" != "random.img" ]; then
        extension=$(echo ${filename,,} | \
        cut -b$(expr ${#filename} - 2)-${#filename})
        if [ "$extension" == "jpg" ] \
          || ["$extension" == "png" ] \
          || [ "$extension" == "svg" ]; then
          fileArray[$i]=$(echo $filename)
          i=$(expr $i + 1)
        fi
      fi
    fi
done << EOF
    $(grep deleted="false -A7 ~/.gnome2/backgrounds.xml)
EOF
fileArrayLength=`echo $[ ( $RANDOM % ${#fileArray[@]} ) ]`
cp "${fileArray[$fileArrayLength]}" "$installedDir/random.img"

Save the file as gRandomBackground.sh in a directory (this example uses: “/home/$USER/Pictures/backgrounds/random”, if you install it elsewhere, be sure to change the $installedDir variable in the script)
Open Terminal and enter the command: crontab -e If you haven’t used crontab before, stick with the default, nano
Paste the following as one line into the editor: 0 */3 * * * bash ~/Pictures/backgrounds/random/gRandomBackground.sh This will change the background every three hours, on the hour. “Ctrl+O, and then Ctrl+W” should get the crontab saved and also get you exited out of nano. For more information on how to use cron, see Google.
Open up the Appearance Preferences dialog again, by right-clicking on the desktop and selecting Change Desktop Background
Click the Add… button and browse to the directory that gRandomBackground.sh is installed to
Select the random.img background, click the Open button, and then the Close button

Your background should change every three hours.