open INPUT, "$ENV{HOME}/flat_file"
   or die $!;

my %ports;
while (my $line = <INPUT>) {
    chomp $line;
    my ($code, $city) = split /\|/, $line; 
    $ports{$code} = $city
       if not $ports{$code};
}

for my $key (keys %ports) {
    if ($ARGV[1] =~ /$key/) {
        print $ports{$key}, "\n";
    }
}

close INPUT;