use strict;

my  $infile = 'input.txt';
my  $otfile = 'output.txt';
my  $token;
our @outfile;

# Read existing output file into array
open my $ot, '<', $otfile or die "$otfile: $!\n";
while (<$ot>) {
	push @outfile, $_;
}
close $ot;

# Iterate over input file appending rows to array
open my $in, '<', $infile or die "$infile: $!\n";
while (<$in>) {
	(undef, $token, undef) = split /\W/, $_;
	&insert($token, $_) if $token;
}
close $in;

# Replace output file eliminating blank lines
open $ot, '>', $otfile or die "$otfile: $!\n";
foreach my $line(@outfile) {
	print $ot $line if $line !~ /^ ?\n/;
}

exit 0;


# Insert the line into @outfile at the correct place
sub insert {
	my $token;
	my $flag = 0;
	for (my $i; $i < @outfile; $i++) {
		(undef, $token, undef) = split /\W/, $outfile[$i];
		$flag = 1 if $token eq $_[0];
		if ($flag and $token ne $_[0]) {
			print "$_[0]\n";
			splice @outfile, $i, 0, $_[1];
			$flag = 0;
		}
	}
}