hash... * exists * delete variable... * defined * undef

undef_vs_delete.pl

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

use Data::Dumper;

my %hash = (
        key1 => 'value1',
        key2 => 'value2',
        key3 => 'value3',
);

print "-------------------\n";
print "undef\n";
print "-------------------\n";
{
        undef $hash{key2};
        #{
        #  'key2' => undef,
        #  'key1' => 'value1',
        #  'key3' => 'value3'
        #};

        if (defined $hash{key2}) {
                print "key2 is defined\n";
        }
        else {
                print "key2 is NOT defined\n";
        }
        if (exists $hash{key2}) {
                print "key2 is exists\n";
        }
        else {
                print "key2 is exists\n";
        }

        print Dumper \%hash;
}


print "-------------------\n";
print "delete\n";
print "-------------------\n";
{
        delete $hash{key2};
        #{
        #  'key1' => 'value1',
        #  'key3' => 'value3'
        #};
        if (defined $hash{key2}) {
                print "key2 is defined\n";
        }
        else {
                print "key2 is NOT defined\n";
        }
        if (exists $hash{key2}) {
                print "key2 is exists\n";
        }
        else {
                print "key2 is exists\n";
        }
        print Dumper \%hash;
}

__END__

hash
exists
delete

variable
defined
undef




-------------------
undef
-------------------
key2 is NOT defined
key2 is exists
$VAR1 = {
          'key2' => undef,
          'key1' => 'value1',
          'key3' => 'value3'
        };
-------------------
delete
-------------------
key2 is NOT defined
key2 is exists
$VAR1 = {
          'key1' => 'value1',
          'key3' => 'value3'
        };