#!/usr/bin/perl
use strict;
use warnings;

my @hand = qw (a b c d);
my @ch;
for my $k (@hand)
{
  push(@ch,$k);
  for my $lst (@ch)
  {
    push (@ch, $k.$lst) if index($lst,$k)==-1;
  }
}

print join("\n",@ch)."\n";