spawn_once.lua

-- {{{
--
-- Autostarting for Awesome <3.4!
-- Add this section to the end of your rc.lua
-- configuration file within ~/.config/awesome/rc.lua
--
-- If you're using Awesome 3.5 change: 
--    add_signal -> connect_signal 
--    remove_signal --> disconnect_signal
--
-- Thanks to eri_trabiccolo as well as  psychon
--
function spawn_once(command, class, tag) 
  -- create move callback
  local callback 
  callback = function(c) 
    if c.class == class then 
      awful.client.movetotag(tag, c) 
      client.remove_signal("manage", callback) 
    end 
  end 
  client.add_signal("manage", callback) 
  -- now check if not already running!     
  local findme = command
  local firstspace = findme:find(" ")
  if firstspace then
    findme = findme:sub(0, firstspace-1)
  end
  -- finally run it
  awful.util.spawn_with_shell("pgrep -u $USER -x " .. findme .. " > /dev/null || (" .. command .. ")")
end

-- use the spawn_once
spawn_once("subl", "Sublime_text", tags[1][2])
spawn_once("chromium", "Chromium", tags[1][3])
spawn_once("thunar", "Thunar", tags[1][4])
spawn_once("xchat", "Xchat", tags[1][5])
-- }}}