use strict;
use Algorithm::Loops qw/ NestedLoops /;

my @arrays = (
  [qw/ a b c /],
  [qw/ d e /],
  [qw/ f g h /],
  [qw/ i /],
  [qw/ j k /],
  [qw/ l /],
  [qw/ m /],
);
NestedLoops(
  [ map [ undef, @$_ ], @arrays ],  
  sub {
    my $count = 0;
    my $string = join '', grep { defined && ++$count } @_;
    print $string if $count >= 4;
  },
);