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

my @stack = [];

for (split /([\[\],])/, $test) {
    next
      unless length $_;

    next
      if $_ eq ',';

    push @stack, [] and next
      if $_ eq '[';

    push @{ $stack[-2] }, pop @stack and next
      if $_ eq ']';

    push @{ $stack[-1] }, $_;
}

my $retval = $stack[0];