Show us the code you tried. For that desired output, the modifications to the code I posted are not that complicated, especially with the suggestions that I already made. What I already said about collecting values from MYFILE will still work. Here are some additional hints to create the output you want:

• For each line from NEWF, you need to check the index in column 5 and the A/B label in the last column. You get your hands on each of those with something like this:

  my @fields = ( split /\s+/ );           # need to hold on to all field
  +s for later
  my( $index, $label ) = @fields[4, -1];  # this is an array slice
  [download]

• Now that you know the index and the label for a line, you use them to find the proper value from one of the arrays you created while reading from MYFILE (e.g., @a_vals or @b_vals if you followed my example). As I mentioned, before, you can use if/else to do that but a nicer way is with given/when (as long as your Perl is 5.10.0 or newer). Here's a suggestion but note that it will not work as written here. $x and $y are not declared. You need to replace them with the correct value from @a_vals or @b_vals (HINT: use $index from above).

  use 5.010;
  
  given( $label ) {
      when ( 'A' ) { $fields[ -2 ] = $x; }
      when ( 'B' ) { $fields[ -2 ] = $y; }
      default { say "OOPS!  bad label"; }
  }
  [download]

• Now you can print the result:

  say join "\t", @fields;    # separates fields with TAB
  [download]

That's all there is to it. Give it another go and post back with your code if you need more help.

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