form to file script. php or html
 

Hey, Im looking for a html, or php simple script that will be able to have a form with a field, that when submitted will send it to a text file on my server. the php or html script will also be on the same server.

Also it needs to replace everything else in the text file when a new thing is submitted.

Ive tried searching and couldnt find anything.
Any help would be appreciated.