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

my $filename = shift // '1001.nc';
my $arg1 = shift // 0;

open(my $fh, '<:encoding(UTF-8)', $filename) or die "Could not open file '$filename' $!";

my ($g, $f) = ('G', 'F');
while (my $row = <$fh>) {
    $row =~ s/\r?\n$//;
    my $newrow;
    for my $word (split / /, $row){
        given (substr($word, 0, 1)) {
            when ('N') { next if $arg1 == 1 }
            when ('G') { if ($word ne $g) { $g = $word } else { next } }
            when ('F') { if ($word ne $f) { $f = $word } else { next } }
        }
        $newrow .= " $word";
    }
    $newrow =~ s/^\s+|\s+$//g;
    say $newrow;
}