Implementing a fixed-size log file, or a circular buffer on disk

I checked this question, but it's not what I'm looking for.

I'm trying to figure out how to cap a log file's size (say, 10MB), and as soon as it's hit, either:

• start writing to the beginning, rather than appending, or
• keep appending, but delete the contents from the beginning as I do so

Don't really care about language - as long as it's possible :)

Note: I am aware of the rolling log files approach (hit a target size, rename, and continue logging). I am looking to avoid such a roll.