Run once with awesome session

-- Autostart with Awesome session
function run_once(prg,arg_string,pname,screen)
    if not prg then
        do return nil end
    end

    if not pname then
       pname = prg
    end

    if not arg_string then
        awful.util.spawn_with_shell("pgrep -f -u $USER -x '" .. pname .. "' || (" .. prg .. ")",screen)
    else
        awful.util.spawn_with_shell("pgrep -f -u $USER -x '" .. pname .. " ".. arg_string .."' || (" .. prg .. " " .. arg_string .. ")",screen)
    end
end

run_once("urxvtd","--quiet --opendisplay --fork")