Note that when combining `when` with `with_items` (see :doc:`playbooks_loops`), be aware that the `when` statement is processed separately for each item. This is by design::
The variable 'ansible_os_family' is being interpolated into
the list of filenames being defined for vars_files.
As a reminder, the various YAML files contain just keys and values::
---
# for vars/CentOS.yml
apache: httpd
somethingelse: 42
How does this work? If the operating system was 'CentOS', the first file Ansible would try to import
would be 'vars/CentOS.yml', followed by '/vars/os_defaults.yml' if that file
did not exist. If no files in the list were found, an error would be raised.
On Debian, it would instead first look towards 'vars/Debian.yml' instead of 'vars/CentOS.yml', before
falling back on 'vars/os_defaults.yml'. Pretty simple.
To use this conditional import feature, you'll need facter or ohai installed prior to running the playbook, but
you can of course push this out with Ansible if you like::
# for facter
ansible -m yum -a "pkg=facter ensure=installed"
ansible -m yum -a "pkg=ruby-json ensure=installed"
# for ohai
ansible -m yum -a "pkg=ohai ensure=installed"
Ansible's approach to configuration -- separating variables from tasks, keeps your playbooks
from turning into arbitrary code with ugly nested ifs, conditionals, and so on - and results
in more streamlined & auditable configuration rules -- especially because there are a
minimum of decision points to track.
Selecting Files And Templates Based On Variables
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..note:: This is an advanced topic that is infrequently used. You can probably skip this section.
Sometimes a configuration file you want to copy, or a template you will use may depend on a variable.
The following construct selects the first available file appropriate for the variables of a given host, which is often much cleaner than putting a lot of if conditionals in a template.
The following example shows how to template out a configuration file that was very different between, say, CentOS and Debian::
Often in a playbook it may be useful to store the result of a given command in a variable and access
it later. Use of the command module in this way can in many ways eliminate the need to write site specific facts, for
instance, you could test for the existence of a particular program.
The 'register' keyword decides what variable to save a result in. The resulting variables can be used in templates, action lines, or *when* statements. It looks like this (in an obviously trivial example)::
- name: test play
hosts: all
tasks:
- shell: cat /etc/motd
register: motd_contents
- shell: echo "motd contains the word hi"
when: motd_contents.stdout.find('hi') != -1
As shown previously, the registered variable's string contents are accessible with the 'stdout' value.
The registered result can be used in the "with_items" of a task if it is converted into
a list (or already is a list) as shown below. "stdout_lines" is already available on the object as
well though you could also call "home_dirs.stdout.split()" if you wanted, and could split by other
fields::
- name: registered variable usage as a with_items list
