local awful = require("awful")
local lfs   = require("lfs")

local function processwalker()
   local function yieldprocess()
      for dir in lfs.dir("/proc") do
        if tonumber(dir) ~= nil then
          local f, err = io.open("/proc/"..dir.."/cmdline")
          if f then
            local cmdline = f:read("*all")
            f:close()
            if cmdline ~= "" then
              coroutine.yield(cmdline)
            end
          end
        end
      end
    end
    return coroutine.wrap(yieldprocess)
end

function run_once(process, cmd)
   assert(type(process) == "string")
   local regex_killer = {
      ["+"]  = "%+", ["-"] = "%-",
      ["*"]  = "%*", ["?"]  = "%?" }

   for p in processwalker() do
      if p:find(process:gsub("[-+?*]", regex_killer)) then
         return
      end
   end
   return awful.spawn(cmd or process)
end
-- run once END