Idempotent augeas

idempotent.rb

# We want a function that makes it easier to write down how
# to make idempotent changes with augeas rather than the
# clunky mechanism the augeas Puppet type gives you today.
#
# I was thinking we could achieve this with a function like the following:
augchange(
  :find => "/files/etc/hosts/*[ipaddr = '127.0.0.1']",
  :create => ["ins 01 before /files/etc/hosts/*[1]",
              "set /files/etc/hosts/01/ipaddr 127.0.0.1"],
  :tree => {
    "ipaddr" => "127.0.0.1",
    "canonical" => "localhost",
    "alias" => ["localhost.localdomain",  "localhost4"]
  }
}

# The parameters are as follows:
# :find : a path expression that finds the root of the tree we want to change
# :create : a sequence of statements that make it so that :find will find somehting,
#           will only be run if :find doesn't find something initially. If it is
#           the special value :find, we just do a 'clear <find>' with the path expression
#           of :find
# :tree : the tree that should be constructed at the node that :find finds.
#         If the value of an entry is an array, a series of nodes with that name is created
augchange(
  :find => "/files/etc/ssh/sshd_config/PermitRootLogin",
  :create => :find
  :tree => { "." => "no" }
)

Lines 10-14: the tree might be better represented as an array than a hash - it has a more predictable order (hashes are insertion order, which makes it difficult to change).