use IO::File;
my $file = IO::File->new;
$file->open('< data.dat') or die("Can't read the source:$!");

until ($file->eof) {
   my $line = $file->getline();
   # the regex below will find lines that start with 'NU '
   # and have the other fields you want somewhere, surrounded
   # with spaces.  YMMV.
   if ($line =~ /^NU \s .* \s U \s .* \s Pu \s/sx ) {
      # we want to get the values from the next line
      # first, we find the column indexes we want...
      my @col = split(qr/\s/s, $line); #split on whitespace
      my %index;
      for (0..@col-1) {
         $index{$1} = $_ if $col[$_] =~ /^(NU|U|Pu)$/;
      }
      
      # now we get the next line and split it into columns
      $line = $file->getline();
      chomp($line);
      @col = split(qr/\s/s, $line); # we can safely reuse @col
      
      # now print the appropriate values using the indexes we captured
+.
      foreach (keys %index) {
         printf "%3s = '%s'\n", $_, $col[$index{$_}];
      }
   } # end of if
} # end of until
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