#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use File::ReadBackwards;

my $numlines = 20;
my $filename = 'in.log';

my $bw = File::ReadBackwards->new($filename)
    or die "can't read $filename $!";

my @lines;
my $count = 0;
while( defined( my $line = $bw->readline ) ) {
    chomp $line;
    push @lines, $line;
    $count++;
    last if $count == $numlines;
}

@lines = reverse @lines;

print Dumper \@lines;

__END__

$ perl reverse_file.pl
$VAR1 = [
          'line 2',
          'line 3',
          'line 4',
          'line 5',
          'line 6',
          'line 7',
          'line 8',
          'line 9',
          'line 10',
          'line 11',
          'line 12',
          'line 13',
          'line 14',
          'line 15',
          'line 16',
          'line 17',
          'line 18',
          'line 19',
          'line 20',
          'line 21'
        ];