Your lastn is on the right track, but you're probably causing too much overhead by reading a byte at a time. Consider something like this (python-y pseudocode; I had a real implementation once at $job[-2] but I don't remember what I did with it):
BLOCKSIZE = 1024 (or so) lines = 0 ; lines_wanted = 10 seek to end of file while lines < lines_wanted seek back BLOCKSIZE bytes read block into buffer pos = end of buffer while pos > 0 use rindex to find \n starting at pos if found lines++ pos = index of \n else last
Update: You of course need error checking on seeks to make sure that you don't try and go back past the beginning of the file. And you would want to remember where the buffer starts so that you can use that (plus pos) to determine where to seek to when you start reading forwards.
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