In addition to stevieb's correct answer, I'll add: there's no such thing as "NULL" in Perl, so that may cause some confusion. Values in Perl may be defined or undefined, as well as true or false. But references (pointers to other things) are always defined and true, even if the thing they point to is empty, as in the case of a hash with no keys and values. 

#!/usr/bin/env perl
use 5.010; use warnings; use strict;

my %hash = ();    # create empty hash
my $ref = \%hash; # create reference pointing to empty hash

if($ref){
    say 'Reference is true';   # <- always true
} else {
    say 'Reference is false';
}

if (%$ref){ # derefence hash and check the number of elements in it
    say 'Hash has elements';
} else {
    say 'Hash is empty';    # <-- hash has no elements
}

$hash{a} = 1;  # add a key and value to hash

if (%$ref){ # derefence hash and check the number of elements in it
    say 'Hash has elements';    # <-- now it has one key and one value
} else {
    say 'Hash is empty';
}

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Aaron B.
Available for small or large Perl jobs and *nix system administration; see my home node.

In reply to Re^6: how to identify a null hash value by aaron_baugher
in thread how to identify a null hash value by smartyollie

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