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

while (<>)
{
   # If we find our line with the column names,
   if (m/$marker/)
   {
      # Read the following line to look for their numbers.
      $_ = <>;
      if (m/$columns/)
      {
         print "NP = $1, U = $2, Pu = $3\n";
      }
      else
      {
         print "Line after NP/U/Pu doesn't give numbers.\n";
      }
   }
}