evince test/te --*tab*--> evince test/test.pdf

local function shellcomp(command,cur_pos,ncomp)
   return awful.completion.shell(command,cur_pos,ncomp,"bash")
end

local function run_promptbox()
   awful.prompt.run{
   prompt = 'Run: ',
   text = '',
   textbox= awful.screen.focused().mypromptbox.widget,
   completion_callback=shellcomp
   }
end

awful.key({ modkey },  "r", run_promptbox,  {description = "run prompt", group = "launcher"}),