Perl array of hashes, keys return an error

Question

I have this code where array is an array of hashes:

my $hash = $array[0];
print "REF: " . ref($hash) . "\n";
my @names = keys ($hash);

The REF prints HASH so I know it is a hash.

But then the keys function returns an error:

Type of arg 1 to keys must be hash

How can I use the $hash as a hash?

Thanks!

The REF prints HASH so you know it is a reference to a hash. — ikegami
– ikegami, Commented Mar 3, 2015 at 13:23

Sobrique · Accepted Answer · 2015-03-03 11:23:49Z

1

$hash isn't a hash, it's a hash reference. Therefore you need to dereference it before you can run keys on it.

Simplest way of doing this:

keys %$hash;

e.g.

foreach my $key ( keys %$hash ) {
    print $key, " => ", $hash -> {$key},"\n"; 
}

And yes, I am mixing two dereference methods deliberately. The -> notation says 'dereference this' - it's commonly used for object oriented stuff.

For more complex dereferencing %$hash{'key'} is ambiguous, so you start needing brackets - %{$hash{'key'}} for example.

See:

answered Mar 3, 2015 at 11:17

Sobrique

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