use warnings;
use strict;
use Tie::File;

my @file;
my $template = 'test.dat';

my $o = tie @file, 'Tie::File', $template, recsep => "\r\n"; 
$o->flock;

my @array = @file;
untie @file;

open (WRITE, ">test.dat");

foreach (@array) {
    if (/one/) {
	print WRITE "foo\n";
    }	
}

close WRITE;