Count the lines in the file ( how to do this is documented in perlfaq ), subtract 20000 from that number
and put the result in $start_at, then open the logfile for reading, incrementing the counter for each
line read in and ignore until you've hit $start_at ...
A far better way is to use seek to jump
right to the end of the file. Just go back far enough so
that you know you are getting the chunk that you need,
since seek deals in bytes, not lines. A quick example:
#!/usr/bin/perl
use strict;
my $bigfile = shift or die "Usage: $0 filename <lines>\n";
my $charsperline = 80; ## A rough guess, adjust as needed
my $linesback = shift || 10; ## How many "lines" back to read
open(BIG, $bigfile) or die "Could not open $bigfile: $!\n";
## Make a reasonable guess as to how far back to go.
my $gobackchars = $linesback*$charsperline;
## Figure out how big it is, so we don't go *too* dar back:
my $filesize = -s $bigfile;
$gobackchars = $filesize if $gobackchars > $filesize;
## Go to the end of the file minus that many characters
seek(BIG,-$gobackchars,2);
## We probably arrived in the middle of a line,
## so throw out everything until the start of a new line
## (As determined by $/)
<BIG>;
## Now we print out the rest of the lines:
print while(<BIG>);
close(BIG);
<!- Bam! -->
Update: Sorry, arturo. Some days
(especially rainy Mondays) I need large <HUMOR>
tags wrapped around things. :)