Question

$h below is an object, but it only contains a regular hash.

my $h = YAML::Syck::LoadFile('have_seen.yaml');

If it was a normal hash then the number of keys would just be keys $h.

Question

How to get the numbers of keys when the hash is in an object?

Update

This is code

#!/usr/bin/perl

use strict;
use YAML::Syck;

my $h = YAML::Syck::LoadFile('h.yaml');

my $links = 100;

print $links - keys $h . "\n";

The yaml file contains

--- 
010711: 1
---

Answer 1

$h is not an object, but a plain hashref. This is really an operator precedence problem. Use parentheses to bind the argument to the keys function tight.

print $links - keys($h) . "\n";

As Greg Bacon pointed out, on old Perls it is necessary to manually dereference first with %$h or %{ $h } (which is the better style).