Paul Reinheimer wrote an article on a bug he was trying to solve.
He wrote:
Something I would love to have: An application that watched a file on disk, reporting all versions of the file over time. tail -f wont work as the file is a single line long, the line is changed but no new lines are added. I'm aware of similar tools for windows, none for mac/linux.
If you want to watch the last lines of a file to see when it changes, try this in linux: