Well, all of the discussion about benchmarks set me to wondering which was the most efficient. So here are the actual results. Bear in mind that the benchmarks were only repeated twice and it is a working server. The times where obtained by...

$ticks = time();
....
$ticks = time() - $ticks;
print "$count Records updated in $ticks seconds\n";
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The program is moving data from one MySQL database to another. The subroutine gets passed a hash_ref to a map and a hash_ref from the source database as returned by $query->fetchrow_hashref. The map looks like...

my(%map) = qq(  'AMNT_PAID',            '0.0',
                'AMOUNT',               '{PurchAmt}',
                'DELIVERY_NOTE',        '"{Delivery}"',
                'EXPORTED',             'IF({Exported}, "Y", "N")',
                'FUNDS',                'IF("{CompanyID}"="BCU", "USD"
+, "CAD")');
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The makemap sub returns a string that can be used in the SET portion of an INSERT sql statement. The code snippet follows.

# Create a set list from the data and the data map

sub makemap {

   my($map, $r) = @_;
   my($key, $result, $t, %h, $ndx);
   %h=%$r;
   $result="";

   foreach $key (sort(keys(%$map))) { 
      #print "$key:\t$map->{$key}\n";
      $t = $map->{$key};
        # substitute the actual value for the placeholder fieldname
      $t =~ s/(\{\S+\})/defined(eval("\$h$1")) ? eval("\$h$1") : "NULL
+"/eg;
        # replace any double quotes with escaped doubles
      if ((substr($t,0,1) eq '"') && (length($t) > 2)) {
# best 196 sec
#          $ndx = 1;
#          while( ($ndx = index($t, '"', $ndx)) != -1 and ++$ndx < len
+gth($t)) {
#             substr($t, $ndx++, 0, '"');
#          }
# original 198 sec
#          for ($ndx=1; $ndx < length($t)-1; $ndx++) {
#              if (substr($t,$ndx,1) eq '"') {
#                 substr($t,$ndx,1) = '""';
#                 $ndx++;
#             }
#          }
# substring 204 sec
#         substr($t, 1, -1) =~ s/"/""/g;
# zero width assertion 201 sec 
          $t =~ s/(?<=.)"(?=.)/""/g;
      }
      #print "$t\n";
      $result .= qq($key=$t ,);
   }
   chop($result);       # remove trailing ,
   return($result);
}
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Averaged over two runs each with 17400 records with 750 "pathological" records (with embedded double quotes)the results seem to indicate the iterative method is faster than the regex way but I like the elegance of the regular expression.