my @nc;
my %seen;
while (<$fh>) {
    chomp;
    push @nc, $_ if !$seen{$_}++;
}
[download]

Or if your input is guaranteed to be sorted,

my @nc;
my $last;
while (<$fh>) {
    chomp;
    push @nc, $last = $_ if !defined($last) || $last ne $_;
}
[download]