c:\@Work\Perl>perl -wMstrict -le
"my $master = 'comp.hw.new.';
 ;;
 my @items = qw(
   comp.hw. comp.hw.new. comp.hw.hw. comp.sw.old. muse.hw.new. ancient.
   );
 ;;
 LEVEL:
 for my $level (1 .. 4) {
   print qq{Match Level: $level};
   ;;
   my ($buf) = $master =~ m{ \A (?: [^.]* [.]){$level} }xmsg
     or print qq{no master match at level $level};
   next LEVEL unless defined $buf;
   print qq{  Master: '$buf'};
   ;;
   for my $str (@items) {
     if ($str =~ m{ \A (?i) \Q$buf\E }xms) {
       print qq{    '$str' matches '$buf'};
       }
     else {
       print qq{    '$str' DOES NOT match '$buf'};
       }
     }
   }
"
Match Level: 1
  Master: 'comp.'
    'comp.hw.' matches 'comp.'
    'comp.hw.new.' matches 'comp.'
    'comp.hw.hw.' matches 'comp.'
    'comp.sw.old.' matches 'comp.'
    'muse.hw.new.' DOES NOT match 'comp.'
    'ancient.' DOES NOT match 'comp.'
Match Level: 2
  Master: 'comp.hw.'
    'comp.hw.' matches 'comp.hw.'
    'comp.hw.new.' matches 'comp.hw.'
    'comp.hw.hw.' matches 'comp.hw.'
    'comp.sw.old.' DOES NOT match 'comp.hw.'
    'muse.hw.new.' DOES NOT match 'comp.hw.'
    'ancient.' DOES NOT match 'comp.hw.'
Match Level: 3
  Master: 'comp.hw.new.'
    'comp.hw.' DOES NOT match 'comp.hw.new.'
    'comp.hw.new.' matches 'comp.hw.new.'
    'comp.hw.hw.' DOES NOT match 'comp.hw.new.'
    'comp.sw.old.' DOES NOT match 'comp.hw.new.'
    'muse.hw.new.' DOES NOT match 'comp.hw.new.'
    'ancient.' DOES NOT match 'comp.hw.new.'
Match Level: 4
no master match at level 4