How to assign file content to chef node attribute

I have fingreprint.txt at the location "#{node['abc.d']}/fingreprint.txt"

The contents of the file are as below:
time="2015-03-25T17:53:12C" level=info msg="SHA1 Fingerprint=7F:D0:19:C5:80:42:66"

Now I want to retrieve the value of fingerprint and assign it to chef attribute
I am using the following ruby block

ruby_block "retrieve_fingerprint" do  
    block do  
        path="#{node['abc.d']}/fingreprint.txt"  
        Chef::Resource::RubyBlock.send(:include, Chef::Mixin::ShellOut)  
        command = 'grep -Po '(?<=Fingerprint=)[^"]*' path '  
        command_out = shell_out(command)  
        node.default['fingerprint'] = command_out.stdout  
    end  
    action :create  
end  

It seems not to be working because of missing escape chars. Please let me know if there is some other way of assigning file content to node attribute