####Try #1

search(:node, 'run_list:"recipe[xenserver::default]"') do |matching_node|
  execute "chef-client" do
    action :run
  end
end

###ERROR

/usr/lib/ruby/gems/1.8/gems/json-1.4.6/lib/json/common.rb:146:in `parse': 375: unexpected token at '"recipe[vm-creation::default] (JSON::ParserError)
  ]
}
'
        from /usr/lib/ruby/gems/1.8/gems/json-1.4.6/lib/json/common.rb:146:in `parse'
        from /usr/lib/ruby/gems/1.8/gems/chef-0.9.8/lib/chef/knife.rb:340:in `edit_data'
        from /usr/lib/ruby/gems/1.8/gems/chef-0.9.8/lib/chef/knife.rb:419:in `create_object'
        from /usr/lib/ruby/gems/1.8/gems/chef-0.9.8/lib/chef/knife/node_create.rb:40:in `run'
        from /usr/lib/ruby/gems/1.8/gems/chef-0.9.8/lib/chef/knife.rb:127:in `run'
        from /usr/lib/ruby/gems/1.8/gems/chef-0.9.8/lib/chef/application/knife.rb:118:in `run'
        from /usr/lib/ruby/gems/1.8/gems/chef-0.9.8/bin/knife:25
        from /usr/bin/knife:19:in `load'
        from /usr/bin/knife:19

#Try 2 - No Error, but no Work..

search(:node, 'run_list:recipe\[xenserver\:\:default\]') do |matching_node|
  execute "chef-client" do
    action :run
  end
end

[root@chef cookbooks]# knife node run_list add FM-01 recipe[vm-creation::default]
{
  "run_list": [
    "recipe[vm-creation::default]"
  ]
}

[Wed, 10 Nov 2010 12:02:21 -0500] WARN: Node chef.millicorp.com has an empty run list.
[Wed, 10 Nov 2010 12:02:21 -0500] INFO: Chef Run complete in 0.244018 seconds