Then decide how big you want your log file to be, divide that number in half, then rotate your log files the way I described. That way your log file will always be between 1/2x - x.
Or you can write a little script to take the head or tail of your file as far as you want into a new file then replace as original.
[Blue]Blue[/Blue] [Dragon]
If I wasn't Blue, I would just be a Dragon...