I suspect an array will be not enough..

More: depending on the order your elements are delcared you may need two parse of the same data. Hashes are useful. Hashes of Hashes (HoH see perldsc ) are powerful.

In plain english would be something like:

Build up a hash to hold association of names with their characteristics by id (HoH: $assoc{ $current_id } = { name => $current_name, $parent => $current_parent } ) Add an exception: if parent is pound put an empty string or undef.

Now you have to recurse the above structure to build up the list of ancestors: foreach id print the name and if has a parent, get the name of his parent and if the latter has a parent get the name of this parent too, and if the latter has a parent...

Recursion! A sub that call itself.. See https://perlmaven.com/recursive-subroutines

UPDATE 21:30 gmt+1 as many monks provided their solution, here is mine, traslating in perl what above stated in english:

use strict;
use warnings;
my %assoc;
while(<DATA>){
    chomp;
    my @fields = split ',',$_;
    $assoc{ $fields[0] } = { 
                name => $fields[2], 
                parent => $fields[1] eq '#' ? '' : $fields[1], 
    }
}

sub get_parents{
    my $href = shift;
    # exit condition first in recursive subs
    return '' unless defined $assoc{ $href->{parent} }{name};
    print "$assoc{ $href->{parent} }{name} ";
    # recursive call
    get_parents( $assoc{ $href->{parent} }  );
}

foreach my $id (keys %assoc){
    print "$assoc{$id}->{name} ";
    get_parents($assoc{$id});
    print "\n";
}


__DATA__
15,10,name3
10,#,name1
12,10,name2
5,12,name4
8,5,name5

#output

name4 name2 name1
name1
name5 name4 name2 name1
name2 name1
name3 name1
[download]

L*