use strict;

sub fiddleHash($)
{
my ($ref_hash) = @_;
delete $ref_hash->{Quantity}{x};
}

sub displayHash($)
{
my ($ref_Hash) = @_;
foreach (keys %{$ref_Hash->{Quantity}})
  {
  print "$_:$ref_Hash->{Quantity}{$_}\n";
  }
}

my %hash1 = (
    Quantity => {
      x => 1,
      y => 2
      }
    );
my %hash2 = %hash1;

print "hash1 before call\n";
print displayHash(\%hash1);
print "hash2 before call\n";
print displayHash(\%hash2);
fiddleHash(\%hash2);
print "hash1 after call\n";
print displayHash(\%hash1);
print "hash2 after call\n";
print displayHash(\%hash2);

[download]
The sub fiddleHash is only supposed to alter hash2 but it also alters hash1
Output: 
hash1 before call
y:2
x:1
hash2 before call
y:2
x:1
hash1 after call
y:2
hash2 after call
y:2

[download]

In reply to changing copy of a hash changes original by edo

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