my $total;
sub Build_totals_shares_for_sedol_Sell_side($$$) {
  my $sedol = shift;
  my $shares = shift;
  my $mySellfirstflag = shift;
  if ($mySellfirstflag eq "YES") {
    %Sellhash = ($sedol => $shares); 
    #Do you mean that with mySellfirst that we should replace the shares,
    #If so, the above line should be $Sellhash{$sedol}=$shares.
    #As it stands now, we replace the entire hash!!
    print "Sell: The $sedol has traded\n$share\n";
  } else {
    if (exists $Sellhash{$sedol}) {
      print "the sedol is in the list so add the shares.\n";
      $Sellhash{"$sedol"} += $shares;
      my $newtotal = $Sellhash{"$sedol"};
      print "the new total shares for sedol: $sedol is $newtotal\n";
    } else {
      $Sellhash{$sedol} = $shares; #You did a .= here was that a typo?
      print "the new entry is $sedol $shares\n";  
    } 
    $total=0;
    $total += $_ foreach values %Sellhash;
  }
}