Re: pure perl tail revisited

[Aristotle]

The "linux only" comment is obsolete in your updated version.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.

[zentara]

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.