my $marker =
  qr/^\s*   NP  \s+   U   \s+  Pu   \s* $/x;
my $columns =
  qr/^\s* (\d+) \s+ (\d+) \s+ (\d+) \s* $/x;

my $found;

while (<>)
{
  # looking for markers
  if (not $found)
  {
    $found = 1 if ($marker);
  }
  # found markers, get columns
  else
  {
    my ($NP, $U, $Pu);
    if ( ($NP, $U, $Pu) = /$columns/ )
    {
       do_something_with( $NP, $U, $Pu);
    }
    else
    {
      warn "Didn't see columns, ";
    }
    # reset to look for more markers
    $found = 0;
  }
}

##</code><code>##

$found = 0;