Here's a start, which doesn't use lookahead assertions. It works on your tests case, but I would throw more tests cases at it before putting it into production.

local $_ = "this, that, those, these (not enough, nope, never), there"
+;

while ( /(?:^|, )([^,]+\(.*?\)|[^,]+)/g ) {
    print $1, "\n";
}
[download]

1. at the beginning of a string, a word followed by a parenthetical
2. at the beginning of a string, a word
3. following ", ", a word followed by a parenthetical
4. following ", ", a word

That looks pretty good, but it doesn't deal with multiple levels of parens. I think Text::Balanced is really the better solution.

-sam

... but it doesn't deal with multiple levels of parens.

Coding now to deal with nested parens would be solving a problem that hasn't been presented. There might or might not be nested parens in the data. I'd wait for the "customer" to clarify their requirements before hitting this with a larger hammer. YMMV.

local $_ = "this, (that, those), these ((not enough, (nope)), never), 
+there";
(my $re=$_)=~s/((\()|(\))|.)/${[')','']}[!$3]\Q$1\E${['(','']}[!$2]/gs
+;
$re= join'|',map{quotemeta}eval{/$re/};
die $@ if $@ =~ /unmatched/;
while( /((?:$re|[^,])*)/g ){
    print "$1\n";
}
[download]

Can you show an example that works? I don't think Text::CSV_XS will work with embedded, unescaped, commas in a CSV.

-sam

If you have any control over the format, you might consider changing it to match the CSV spec - something standard. Then Text::CSV will help you. The example below is only slightly modified from the examples in the POD

#!/usr/bin/perl -w
use strict;
use Text::CSV_XS;

while( <DATA> ){
  my $line = $_;
  my @input;
  my $csv = Text::CSV_XS->new({  # defaults are: ["]["][,][0]
      quote_char  => '"',
      escape_char => '"',
      sep_char    => ',',
      binary      => 0
  });
  if( $csv->parse( $line ) ){
    @input = $csv->fields;
  } else {
    my $err = $csv->error_input;
    warn "Text::CSV_XS->parse() failed in line $. on argument '"
      , $err, "'\n";
  }
  foreach my $item (@input){
    print "$item\n";
  }
  print "\n";
}

# first line parses 'correctly' - second does not.
__DATA__
this,that,those,"these (not enough, nope, never)",there
this, that, those, these (not enough, nope, never), there
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Excluding embeded paranthesis (which the poster did not mentioned), tr%()%""% would solve the grouping problem for CSV.

--
perl -pew "s/\b;([mnst])/'$1/g"

If the whole field were in parenthesis, you're right, that would work.

But the value is this:
, these (not enough, nope, never),
...not this...
, (these not enough, nope, never),

Text::CSV_XS chokes if you replace the parens with your tr/// suggestion. CSV requires that either the whole field or none of the field be quoted - you can't quote part of a field.

use perl6 (:regexes); # :-)
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Several people have mentioned CSV, but I think your real solution is probabaly to use Test::Balenced to take out the parens properly, and then use a regex to split the data up. Text::Balenced is wildly useful, so learning for this should pay back for other parsing needs. Regexes alone often aren't enough for parsing (at least, not if you want maintainable code).

1. Why do you need to have them split that way? (What is the ultimate goal you're trying to achieve using that data?)
   
   
2. Do you have any control over how the initial data is structured? Smarter data structures make for easier maintenance.

1) because I want to store them in a database, each column represents a field.

2) Nope it was an excel sheet, I exported it to CSV.

I can change the format, but that is what I want to avoid, because i would have to do it manualy

For what its worth, one way of doing this is to keep a count of how many brackets are open and process the string character by character, splitting the string when a comma is encountered iff the bracket open count is zero.

However it strikes me that this is not a particularly perl-ish way to solve the problem although if you are interested I have written such code as part of a Java compiler I wrote I while back

Abh

well, thanks for all your answers guys, I fixed it myself this way:

my @temp;
if (/(.*)(\([\d\w\s,\.]+?\))(.*)/) {
         @temp = split /,/, $1;
         $temp[@temp-1] .= $2;
         my $last = $3;
         $last =~ s/^,+//;
         my @temp2 = split /,/, $last;
         push (@temp, @temp2);
} else {
         @temp = split /,/, $_;
}
[download]

I know it's not generic, but it is something I only had to do once