Sure. I saw all of these. (Though I do not see any reply by davorg). They are all exact, not estimated. The key here is "estimated because the file is Very, Very Large." Reading the whole file may be unacceptable.
Re^2: Estimate line count in text file
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My mistake, I was referring to davidrw's reply. I would suggest (if you have not already done so) benchmarking their Tie::File solution with some 'large' files, since peoples definition of what constitutes a large file differs :)