c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my @WORDS = qw(trying helping doing do xdo help hel xhelp);
 my $s = 'help';
 ;;
 my @hits = grep m{ \A \Q$s\E }xms, @WORDS;
 dd \@hits;
 ;;
 $s = 'do';
 @hits = grep index($_, $s) == 0, @WORDS;
 dd \@hits;
 ;;
 dd \@WORDS;
"
["helping", "help"]

["doing", "do"]

["trying", "helping", "doing", "do", "xdo", "help", "hel", "xhelp"]

##</code><code>##

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"]

[]