how to make the contents of a file disappear after x numbers of days or at date

[Nils Kassube]

user1 wrote:
> Anybody know of a way to make the contents of a file (txt, html,
> jpeg, png, mp3, ogg etc.) disappear after a certain number of days.
> 
> To make the whole content or a selected part of a file to disappear.
> 
> The charateristic must be hidden in the file and not to be removed by
> a copy.
> 
> I should be a kind of wipe operation :-)

Can you explain what you mean with "disappear"? Should the result be an 
empty file or e.g. a file with the same length and random data?


Nils