/(.)*/s

##</code><code>##

  'abcd' =~ /(?:(.)(.))*/s

##</code><code>##

  'abcd' =~ /(?:(.){2})*/s

##</code><code>##

  $1 eq 'a'
  $2 eq 'b'
  $3 eq 'c'
  $4 eq 'd'

##</code><code>##

  'abcdx' =~ /(?:(.)(.))*(.)/s

##</code><code>##

  $_ = 'foo bar baz burk | gah';
  my @words;
  /(?:(\w+)\s+(?{push @words => $1}))*/; # Not backtracking safe! See below.
  # Submatches are in @words now.

##</code><code>##

  my @words;
  'foo bar baz baz burk | gah' =~ /
    (?{ local @_words })
    (?:
      (\w+)
      \s+
      (?{ local @_words = (@_words, $1) })
    )+
    (??{ quotemeta $_words[-1] })
    (?{ @words = @_words })
  /x;