my %hash = (foo => {});
my $ref  = \%hash;

for (0..100000) {
   print $_, " ";
   $ref = $ref->{foo};
   $ref->{foo} = {}; 
}

my %hash = (foo => {});
my $ref  = \%hash;

for (0..100000) {
   print $_, " ";
   $ref = $ref->{foo};
   $ref->{foo} = {}; 
}

89232 Segmentation fault

#!/usr/bin/perl

use strict;
use warnings;

my %hash = (foo => {});
my $ref  = \%hash;

for (0..100000) {
  print $_, "\n";
  $ref = $ref->{foo};
  $ref->{foo} = {};
}

#%hash = {}; # <= Speicherzugriffsfehler

my $delete;
$delete=sub {
  my $href=shift(@_);
  $delete->($href->{foo}) if(ref($href->{foo}) eq 'HASH');
  %$href=();
};
$delete->(\%hash);

print "ende\n";