Puppet provides an additional mode of operation, that being the discovery of resources using the puppet resource command. The self.instances method should implement the return of any instances of a particular resource type that the provider is able to find on the underlying system.

The following example illustrates the use of the rpm -qa command to query for all packages installed on the underlying Red Hat system:

Puppet::Type.type(:mynewtype).provide(:yum) do
   ...
   def self.instances
     pkgs = rpm('-qa','--qf','%{NAME} %{VERSION}-%{RELEASE}
')
     pkgs.split("
").collect do |entry|
       name, version = entry.split(' ', 2)
       new( :name => name,
         :ensure => :present,
         :version => version
       )
     end
   end
   ...
 end

Each resource returned by self.instances stores the attributes in the @property_hash instance variable. All the other methods in the provider have access to the property hash, so we could implement the exists? and version methods in our provider in a much simpler way, as shown in the following code:

Puppet::Type.type(:mynewtype).provide(:yum) do
   ...
   def exists?
     @property_hash[:ensure] == :present
   end
 
   def version
     @property_hash[:version]
   end
   ...
 end