#!/usr/bin/perl
use 5.010;
use strict;
use warnings;

my $gene_list = 'gene_list.txt';
open GL, "<", $gene_list or die "Unable to open $gene_list because $!";

my %seen;
while (my $gene = <GL>) {
	$seen{$gene}++;
}
close GL or die "Unable to close $gene_list because $!";

my $hfr = 'HFR_genes.txt';
open HFR, "<", $hfr or die "Unable to open $hfr because $!";

while (my $gene = <HFR>) {
	print if $seen{$gene};
}
close HFR or die "Unable to close $hfr because $!";

##</code><code>##

my %seen;
print grep $seen{$_}++, <>;