gistfile1.rb

default[:networking][:static_hosts] = {}

# read the existing hosts file on first run and preserve any entries found there
f = File.new("/etc/hosts")
static_hosts = {}
f.each_line do |line|
  # ...
  static_hosts[ip] = hostname
  # ...
end
f.close

# preserve any attributes were here before
# self refers to a node object, which is the context in which this file is evaulated
(self[:networking][:static_hosts]).each do |ip, hostname|
  # ...
  static_hosts[ip] = hostname
  # ...
end

# unequivocally set the attribute
set[:networking][:static_hosts] = static_hosts