use strict;
use warnings;
use Data::Dumper;

my $test="[a,b],c,'d',[e,[f,g,h,[i,j],k,l],m,n],o,p";

my @array = split /,/,$test;
my ($open, $current, @res);

foreach (@array)  {
    $current .= $_ if ($current or /\[/);
    $current .= ', ' if !(/\]/);
    $open++ if (/\[/);
    if (/\]/)  {
        $open--;
        $current .= ', ' if ($open) ;
    }

    unless ($open)  {
        if ( $current eq ', ') {
            push @res, $_;
        }
        else  {
            push @res, $current;
        }
        undef $current;
    }
}

print Dumper \@res;
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This code gives you what you want. Hope you are new to post threads in perlmonks and from next time please provide your code and the problem you are facing. It will tell us the way you have proceeded and it gives more understanding on the question.
I am not sure, whether this can be solved easily by using regex in split.