c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my @words = qw(he xhelper hello hel help helper helping);
 my $t = 'helper';
 ;;
 my @hits = grep overlap($_, $t, 3), @words;
 dd \@hits;
 ;;
 @hits = grep overlap($_, $t, 4), @words;
 dd \@hits;
 ;;
 @hits = grep overlap($_, $t, 6), @words;
 dd \@hits;
 ;;
 @hits = grep overlap($_, $t, 7), @words;
 dd \@hits;
 ;;
 sub overlap {
   my ($s, $t, $min) = @_;
   ;;
   return ($s ^ $t) =~ m{ \A \x00{$min,} }xms;
   }
"
["hello", "hel", "help", "helper", "helping"]

["help", "helper", "helping"]

["helper"]

[]