#!/usr/bin/perl -w
use strict;

while (<DATA>)
{
   print "INPUT LINE: $_";

   my @four_constants = 
      grep{/([bBcCdDfFgGhHjJkKlLmMnNpPqQrRsStTvVwWxXzZ]{4,}?)/g}
      split; #the ? allows more than a min of 4!
   next unless @four_constants;
   print "output: @four_constants", "\n";
}

=EXAMPLE OUTPUT

INPUT LINE: xyy xyz
INPUT LINE: bBbB
output: bBbB
INPUT LINE: abc bacx
INPUT LINE: abca    xyzz
INPUT LINE: abCA    XXZZ
output: XXZZ
INPUT LINE: xxyyzzz
INPUT LINE: bckz  klmx
output: bckz klmx
INPUT LINE: BKZXXXXXXXXXXXX
output: BKZXXXXXXXXXXXX


=cut

__DATA__
xyy xyz
bBbB
abc bacx
abca    xyzz
abCA    XXZZ
xxyyzzz
bckz  klmx
BKZXXXXXXXXXXXX