my $s = "abcdefghi";
my @a = ([ 0, 3 ], [ 0, 1 ], [ 1, 2 ], [ 2, 1 ]);
my $qr = matcher(\@a);
match($s, $qr);

sub matcher {
  my $array = shift;
  my(%pos, @undef);
  my($start, $length) = @{ $array->[0] };
  for (1 .. $#$array) { 
    my($pos, $width) = ($array->[$_][0], $array->[$_][1]);
    if (defined $pos) {
      $pos{$pos} .= '(';
      $pos{$pos + $width} .= ')';
    } else {
      push @undef, $_;
    }
  } 
  my $qr = '.' x ($start + $length);
  for (sort { $b <=> $a } keys %pos) { 
    substr $qr, $_, 0, $pos{$_};
  }
  for (reverse @undef) {
    $qr =~ s/((.*?\(){$_})/$1((?!))?/;
  }
  $qr =~ s{(.{$start})}{(?<=^$1)} if $start;
  qr/$qr/;
}