Perl defining undefined keys

Question

The following code prints Key defined 3. Why is Perl defining the key ABC ? I was expecting all the three checks to be false.What am I doing incorrectly ?

#!/usr/bin/perl 
use warnings;
use strict;

my %Hash;

if(defined $Hash{'ABC'})
{
    printf("Key defined 1\n");
}

if(defined $Hash{'ABC'}{'Status'})
{
    printf("Key defined 2\n");
}

if(defined $Hash{'ABC'})
{
    printf("Key defined 3\n");
}

Answer 1

This $Hash{'ABC'}{'Status'} autovivifies the ABC key (see perldoc perlref and wikipedia):

use warnings;
use strict;
use Data::Dumper;

my %Hash;

if(defined $Hash{'ABC'})
{
    printf("Key defined 1\n");
}
print Dumper(\%Hash);

if(defined $Hash{'ABC'}{'Status'})
{
    printf("Key defined 2\n");
}
print Dumper(\%Hash);

if(defined $Hash{'ABC'})
{
    printf("Key defined 3\n");
}
print Dumper(\%Hash);

__END__

$VAR1 = {};
$VAR1 = {
          'ABC' => {}
        };
Key defined 3
$VAR1 = {
          'ABC' => {}
        };

See also Data::Diver and the autovivification pragma, which prevent autovivification.