use strict;
use warnings;
use utf8;

use Test::More tests => 1;

my @in = split (/\n/, <<EOT);
aaa nš 1234, xyz
bbb nš 1234, yzx
ccc nš 1234, yxz
ddd nš 2345, zyx
EOT

my @want = split (/\n/, <<EOT); 
aaa nš 1234, xyz
ddd nš 2345, zyx
EOT

my $number;
my %seen = ( '' => 1 );
my @out;

for my $line (@in) {
    if ($line =~ /nš ([\d]*),/) {
        $number = $1;
    } else {
        $number = '';
    }

    push @out, $line unless $seen{$number}++;
}

is_deeply (\@out, \@want);