1. Rows are delimited by returns. (\r\n or \n depending on the platform, binmode, etc.)
2. Fields within a row are delimited by ",". (When saving in "text" format the separator is often "\t" instead.)
3. Fields may be quoted or unquoted.
4. Quoted fields are literal text that start and end with an unpaired ". Separators, returns, etc can appear within a quoted field, and " can appear doubled.
5. Unquoted fields cannot contain the separator, returns, or quotation marks. They are also subject to some interpretation. For instance numbers may appear in floating point, and an empty field is a null (represented within Perl by undef - very few parsers get this right).
6. It is customary for the first row to be the field names, and for all rows to have the same number of fields.

# Takes an array and returns it as a CSV row
sub format_csv {
  my @fields = @_;
  foreach (@fields) {
    if (not defined($_)) {
      $_ = "";
    }
    elsif (0 == length($_)) {
      $_ = '""';
    }
    elsif (/\s|"|'|,/) {
      s/"/""/g;
      $_ = qq("$_");
    }
  }
  (join ",", @fields) . "\n";
}
[download]

local *FILE;
open (FILE, "> $file") or die "Cannot write '$file': $!";
print FILE format_csv(@cols);
foreach my $row (@data) {
  print FILE format_csv(@$row{@cols});
}
close(FILE) or die "Cannot close '$file': $!";
[download]

and " can appear doubled.

Ouch, that hurts. Mastering Regular Expressions assumes " can be escaped with a backslash.

The regex the book uses is:

"([^"\\]*(\\.[^"\\]*)*)",?|([^,]+),?|,
[download]

Would that introduce Microsoft-incompatability?

U28geW91IGNhbiBhbGwgcm90MTMgY
W5kIHBhY2soKS4gQnV0IGRvIHlvdS
ByZWNvZ25pc2UgQmFzZTY0IHdoZW4
geW91IHNlZSBpdD8gIC0tIEp1ZXJk

Save the following in your text editor and open in Excel to verify the incompatibility.

hello,world
"this","is "",test 1"
"this","is \",test 2"
"this","is "" test 3"
"this","is \" test 4"
[download]

Note in particular the unusual handling of the even tests.

The rules are about: The columns are separated with a special char; if this char is inside a column, then the column is embraced by "" (or sometimes '').

my $csvSep = ','; # comma as csv-separator
foreach my $line (@rows){ # e.g. 2-dim array
  my @columns = @$line;
  print join($csvSep, # join by $csvSep
    map { 
      /\Q$csvSep/ ? "\"$_\"" : $_ # if $csvSep found in Value: "val"
    } @columns; # take columns
  ), "\n"; # and a newline...
} # foreach
[download]

Best regards,
perl -le "s==*F=e=>y~\*martinF~stronat~=>s~[^\w]~~g=>chop,print"

You at least put some effort into this answer, but your code is not sufficient to produce valid output if, for instance, the contents of a field was just a double-quotation mark.

use Text::CSV_XS;
my $csv = Text::CSV->new;

# reading
$csv->parse(<STDIN>);
my @fields = $csv->fields;

#or writing:

$csv->combine(@fields);
print $csv->string;
[download]

Best regards,
perl -le "s==*F=e=>y~\*martinF~stronat~=>s~[^\w]~~g=>chop,print"

Toni, first thing: relax :-)
Second, there's more than one way to do it ;-)
Third, maybe we could be more helpful if we know what you are trying to do, what your limitations are, etc.

For instance, do you need to use Excel? Are you open to another method? What programs are going to be accessing the CSV?

Update!:
This was not a slam on Toni! I was trying to make this person feel more comfortable in all the tension... I should have been more clear. Perhaps I should have said "first thing, it's all good :-)"

It's just that there's this Tibetan guy I know and he is always laughing and saying "relax..."

It's all good.

You know, I find this absolutely incredible:

I was given a negative marking on this post!

Is this not a community of Fellowship? Should we not work together to better ourselves? Was my intention not clearly one of helpfulness?

Why then, the need to lash out? Why can't it be a hand of friendship instead of a hand that seeks to damage?

Perhaps its because you told Toni to chill out. Toni hasn't posted a single node in this thread except for the original question....