my $new_outputfile = $outputfile."_B";

open (RESULT_FILE, "<$outputfile");
open (CLEANED_RESULT, "+>$new_outputfile");

our @data = <RESULT_FILE>;
chomp @data;

my %seen; 

for ( @data) { 
  next if $seen{$_}++;
  print CLEANED_RESULT "$_\n";
}

remove $outputfile or warn $!; 
rename "$new_outputfile", "$outputfile"  or warn $!;