I thought of that, but the problem with tell+seek is that you can't go backwards unless you keep track of all the previous positions. A hybrid solution would do the trick.

my $max_lines = 100;

open(my $fh, '<', $path)
   or die("Unable to open file $path: $!\n");

my $line = $cgi->param('line') || 0;
my $pos  = $cgi->param('pos');

if (defined($pos)) {
   seek($fh, $pos, 0)
      or die("Unable to seek to $pos: $!\n");
} else {
   if ($line) {
      do { <$fh> }
      while $. < $line;
   }
}

my $lines = $max_lines;

print(qq{<div class="lines">\n});
while ($lines-- && defined(my $line = <$fh>)) {
   chomp($line);
   print(html_escape($line), qq{<br>\n});
}
print(qq{</div>\n});

my $first = ($line == 0);
my $last  = not defined(<$fh>);

my $prev_line = $line - $max_lines;
$prev_line = 0 if $prev_line < 0;
my $prev = "?line=$prev_line";

my $next_line = $line + ($max_lines - $lines) - 1;
my $next_pos  = tell($fh);
my $next = "?line=$next_line&pos=$next_pos";

if ($first && $last) {
   print(qq{No other pages.<br>\n});
} else {
   print(qq{<a href="$prev">[prev page]</a> }) if !$first;
   print(qq{<a href="$next">[next page]</a> }) if !$last;
   print(qq{<br>\n});
}
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