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);

[download]
<!- Bam! -->

Update: Sorry, arturo. Some days (especially rainy Mondays) I need large <HUMOR> tags wrapped around things. :)

In reply to Re: Re: How can I read just the end of a huge file? by turnstep
in thread How can I read just the end of a huge file? by vonman

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.