use strict;
use warnings;
use Tie::File;
my $string = "Text to be prepended.\n";
my @array;
{
    my $obj = tie @array, 'Tie::File', "guestbook.txt" 
        or die "Can't open the guestbook file. $!\n";
    $obj->flock;
    unshift @array, $string;
    untie @array;
}