FileStripper allows you to copy off the last portion of a very large diagnostic or debug output file. Sometimes these files can exceed 3 or 4 gigs and they cannot be easily manipulated with normal file handling tools. You can opt to copy the last 10 to 900 megs off the end of any text based file of any size.
Files under 4 gig are very fast. You can chop off 500 megs off the end in 30 seconds or so. Dealing with larger files is much slower. It can be run while Unity is operating, however it does chew up the CPU pretty good. It's best to run it when there's little call traffic or when Unity is off line.

The license of this software is Freeware, you can free download and free use this file management software.