Have the date as the first line of the file. If the dates are different, remove the file.
Have the perl script accept the poll's name from a form hidden. Search only that file.
Of these options, I like the last one best. This will allow you to accurately track the results of your polls.
(as a back up to the main mechanisim.) And it would allow you to keep up past polls. And you could
leave a poll up for longer than a day.