Im not quite sure what you are wanting to end up with but try this:

use strict;
use warnings;

my @array = qw(
  1nkndnfd
  2nsnskdnsdn
  3ddjsjd
  4fksjsdj
  5kdsjdskjdskj
  1ksdjdjsk
  hg
  2dsjskj
  3djkdjsljs
  4fdkkjdskjsk
  5sadjjdjdodjs
  6sadjjdjdodjs
);

foreach (@array) {
    my ( $num, $data ) = /(\d)(.*)/;
    next if ( !length $num || !length $data || $num !~ /[1-5]/ );
    open my $file, '+>>', "round_robin_$num" . ".txt";
    print $file "$num - $data\n";
}
[download]

EDIT: Just noticed other replies, looks this is NOT what he/she was after.