#!/bin/perl
use v5.18;
use warnings;

my ($g, $f) = ('G', 'F');
my $filename = '808.nc';
open(my $fh, '<:encoding(UTF-8)', $filename) or die "Could not open file '$filename' $!";

while (my $row = <$fh>) {
    $row =~ s/\r?\n$//;
    for my $word (split / /, $row){
        say '';
        given (substr($word, 0, 1)) {
            when ('N') { }
            when ('G') { if ($word ne $g) { $g = $word } else { next } }
            when ('F') { if ($word ne $f) { $f = $word } else { next } }
        }
        print " $word";
    }
}