gistfile1.sh

#!/bin/bash

KITTEN_SITE_URL="http://emergencykitten.com"
KITTEN_IMG_FILE=kitten.jpg
KITTEN_SECS=$1

usage(){
        echo "Usage   : $(basename $0) <sleep_time>"
        echo "Exemple : $(basename $0) 60"
        exit 1
}

# Check sleep time arg #
[[ ! $1 =~ [0-9]+ ]] && usage

while true; do
        # Get image URL #
        kitten_img_url=$(curl -s -XGET ${KITTEN_SITE_URL} | grep 'kitten-image' | cut -d'"' -f4)

        # Retrieve image (following redirect) #
        curl -s -o ${KITTEN_IMG_FILE} -L -XGET ${KITTEN_SITE_URL}/${kitten_img_url}

        # Change wallpaper #
        #defaults write com.apple.desktop Background "{default = {ImageFilePath = '${PWD}/${KITTEN_IMG_FILE}'; };}"
        osascript -e "set desktopImage to POSIX file \"${PWD}/${KITTEN_IMG_FILE}\"
        tell application \"Finder\"
            set desktop picture to desktopImage
        end tell"
        sleep ${KITTEN_SECS}
done