use Fcntl;
use Tie::File;

open my $out, ">", "output.txt" or die "$0: open: $!";
my $run = "./SCRIPT.pl";
print $out "##Start of SCRIPT.PL##\n", `$run`;
close $out;

tie my @rows, 'Tie::File', 'output.txt', autochomp => 0 or die "error: $!\n";
print ":$rows[-1]";