open CATEGORY, "categories.txt";  # ...or whatever...

foreach $line ( <CATEGORY> ) {
  @ITEMS = split /\|/, $line;
  foreach $item ( @ITEMS ) {
    ($value, $key) = split /,/, $item;
    $LIST{$key} = $value;
  }
}

close CATEGORY;

open DESC, "descriptions.txt";

# Same code as above, except key/value pairs are reversed.
foreach $line ( <DESC> ) {
  @ITEMS = split /\|/, $line;
  foreach $item ( @ITEMS ) {
    ($key, $value) = split /,/, $item;
    $LIST{$key} = $value;
  }
}
close DESC;

# Now arrange for the output.

open OUTFILE, ">output.txt";
foreach $reference ( sort keys %LIST ) {
  # Sometimes, it's a new category.  These are most important.
  if ( $reference =~ /^\'\w\w\'$/ ) {
    print OUTFILE "\n";
  } else {
    print OUTFILE "|";
  }

  print OUTFILE "$reference,$LIST{$reference}";
}

##</code><code>##

  if ( $reference !~ /^\'\w+\d+\'$/ ) {
    # ...
  }