Switch between two desktop images on OS X e.g. a standard image and a texture for use behind transparent windows like Terminal or MacVim

toggle_desktop_image.rb

#!/usr/bin/env ruby

STD_IMG_REF = '/Users/paulcarey/.std_desktop_image.txt'
IMG_SRC = '/Users/paulcarey/dev/images/ir_black_bg.png'

def current_img
  cmd = "defaults read com.apple.Desktop Background | grep ImageFilePath | tail -n 2 | head -n 1" 
  res = `#{cmd}`
  res = res.split('=')[1].strip
  res[1, res.size - 3]
end

def save_current_img
  File.open(STD_IMG_REF, 'w+') { |f| f.puts current_img }
end

def load_prev_img
  File.open(STD_IMG_REF, 'r') { |f| f.gets.strip }
end

def set_img src
  script = %Q<tell application "Finder"
    set desktop picture to POSIX file "#{src}"
  end tell>
  IO.popen('osascript -', 'w') { |p| p.puts script }
end

if current_img == IMG_SRC
  set_img load_prev_img
else
  save_current_img
  set_img IMG_SRC
end