use strict;

my @data = qw/a mnk ab m b bc abcd cd bcd bd m nk /;
my @result = ();
foreach $a(@data){
	my $is_sub = 0;
	foreach $b(@data){
	  $b =~ /$a/i and length($b) != length($a) and $is_sub = 1 and last;
	}
	push @result,$a unless $is_sub;
  }

print join(",",@result);

# output is: mnk,abcd,bd