nestedvars.yml

---
#######################
# Nested VARS example #
#######################
#
# This example is used to explain how you can call nested variables
# (like, an item of a dictionary) using ansible prior v1.2. It may be
# a bit tricky because of the way ansible does the expansion of th
# evariables...
#
# Bascially, to expand `hostvars[item]` where `hostvars` is a
# dictionary-like object and `item` is a variable, you have to do:
#
#    ${hostvars.{$item}}
#
# Note that the expansion of the dictionary is done with `${...}`
# while the expansion of the attribute of the dictionary is done with
# `{$...}`.
#
# The following example will define a dictionary `hosts`:
#
#     hosts = { 'a': {'b': 'c'}}
#
# and try to print `hosts['a']['b']`
#
- hosts: all
  vars:
    hosts:
      a:
        b: c
    x: a
    y: b
  tasks:
    - debug: msg="${hosts.{$x}.{$y}}"

# The original use case I used for this was taken from this task, in
# which I wanted to produce an ``/etc/hosts`` file starting from the
# data sotred in the inventory, adding or updating the IP addresses of
# all the known hosts.
#
# - hosts: all
#   connection: local
#   tasks: 
#     - lineinfile: dest=/tmp/hostfile regexp=".* $item .*" line="${hostvars.{$item}.ansible_default_ipv4.address} $item "
#       with_items: $hostvars