use strict;
use warnings;

my ($line, $length, $in, $out, $inh, $outh);

$line = 'This is the temp line.';
$in = 'in.dat';
$out = 'out.dat';

$length = length($line) + 1;

open ($inh, $in);
open ($outh, ">$out");

while (<$inh>) { last if $length == length($_) && index($_, $line) != -1; }
while (<$inh>) { print $outh $_; }

close($outh);
close($inh);