200326951|_|rel_Access1|_|200315482|_|
200326951|_|rel_Access1|_|200315786|_|
200326951|_|rel_Access2|_|200315482|_|
200326951|_|rel_Access2|_|200315786|_|

##</code><code>##

my %hash;


open(CMD1, "< test.txt");

while (<CMD1>) {
  my @elts = split(/\|_\|/, $_, -1);
  
  my $p = \\%hash;
  $p = \( ${$p}->{$_} ) for @elts;
}

use Data::Dumper;
print Dumper(\%hash);

##</code><code>##

$VAR1 = {
  '200326951' => {
       'rel_Access2' => {
              '200315482' => {
                               '' => undef
                             },
              '200315786' => undef
            },
       'rel_Access1' => {
          '200315482' => {
                           '' => undef
                         },
          '200315786' => {
                           '' => undef
                         }
        }
     }
};

##</code><code>##

$VAR1 = {
  '200326951' => {
       'rel_Access2' => '200315786' 
            },
       'rel_Access1' => '200315482' 
            }
};