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Re: pure perl tail revisited

by Aristotle (Chancellor)
on Sep 10, 2002 at 16:15 UTC ( #196734=note: print w/replies, xml ) Need Help??


in reply to pure perl tail revisited

The "linux only" comment is obsolete in your updated version. It can still do with some cleaning up. Note this will still fail if the last X lines of the file are larger than 2*200*X bytes, so you cannot compare it against the other solutions as it doesn't do the same thing.
#!/usr/bin/perl -w use strict; die "Usage: $0 file numlines\n" unless @ARGV == 2; my ($filename, $numlines) = @ARGV; # open or die first so that we don't stat a file we don't know exists open my $fh, "<", $filename or die "Couldn't open $filename: $!"; my $chunksize = 2 * 200 * $numlines; my $filesize = -s $fh; $chunksize = $filesize if $filesize < $chunksize; # why seek twice? seek $fh, -$chunksize, 2; my @tail = <$fh>; splice @tail, 0, @tail - $numlines; print @tail; __END__ $ perl -le'print "a"x500 for 1..10' > t.dat $ tailz t.dat 5 | wc -l 1
You need a loop.

Makeshifts last the longest.

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Re: Re: pure perl tail revisited
by zentara (Archbishop) on Sep 11, 2002 at 20:14 UTC
    Thanks for showing me that splice trick. I don't think it took anything off the benchmark times, but it removed the temp array I was using. When I do tailz t.dat 5 | wc -l I get 5. (Just lucky). perl -le'print "a"x5000 for 1..10' > t.dat does give bad results The code still depends on you knowing your max line length beforehand, but I think this is true for more logs and text files. I'm happy now, at least I figured out what Merlyn meant when he said there was a faster method than Tie::File or File::ReadBackwards.

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