Well, if you don't want to use a module, you could try something like the following code - it basically breaks the job down into several parts. The only major requirement is that all your quotes should be valid pairs (you should probably add a test to check that you have an even number of quotes and that you have the number of fields per line that you expect).

1. Pull out the quoted sections
2. Replace ',' with '_comma_' in the quoted sections
3. Restore the quoted sections back into position
4. Safely split on ',' (since quoted commas are now '_comma_')
5. Replace '_comma_' with ','

Here's the code:

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
  $_ =~ s/"[^"]*"/'"' . (shift @quoted) . '"'/ge;
  # now we can safely split on any commas (quoted commas are now '_com
+ma')
  push @output, [split /,/];
  # finally, replace any '_comma_' values with ',' in the latest eleme
+nt of output
  foreach(@{$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
[download]

map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2*$d*$e+$a,$e**2
-$d**2+$b);$c=$d**2+$e**2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20
[download]