unshift makes it simpler:

#!/usr/bin/perl
use strict;
use warnings;
use Tie::File;

my $file = "file.txt";
my $insert = shift @ARGV;
chomp $insert;
my @lines;

tie @lines, 'Tie::File', $file or die $!;
unshift @lines, $insert; # more simple, isn't it?
untie @lines;
[download]

best regards,
neniro