use strict;

my @output;
while(<DATA>){
  chomp;
  next unless $_ =~ /\S/;
  
  # push any quoted stuff (incl. quotes) onto array... (we assume that all quotes are paired)
  push my @quoted, ($_ =~ /"([^"]*)"/g);
  # replace any commas in the array with '_comma_'
  foreach my $quote(@quoted){
    $quote =~ s/,/_comma_/g;
  }
  # now replace the ',' versions with the "_comma_" versions
  $_ =~ s/"[^"]*"/'"' . (shift @quoted) . '"'/ge;
  # now we can safely split on any commas (quoted commas are now '_comma')
  push @output, [split /,/];
  # finally, replace any '_comma_' values with ',' in the latest element of output
  foreach(@{$output[$#output]}){
    s/_comma_/,/g;
  }
}

# what have we got?
foreach(@output){
  foreach(@{$_}){
    print "$_:";
  }
  print "\n";
}

__DATA__
123,456,"hello, world, goodbye, world",789
123,456,"hello, world, goodbye, world",789,"foo, bar","bar, foo"
"hello, world","goodbye, world",123,"foo"
"hello" 123,456,"goodbye, world",789