my $filename = 'counts.txt';
open (my $fh, '>', $filename) or die "Could not open '$filename' $!";

my $count = "";

while (my $line = <>){
	if ($line =~ /^>hsa/){
		$line = <>;
		$count .= length$line;
		$count .= " ";
	}
}

print $fh $count;
close $fh;