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- While working with Ansible

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you will also encounter the
so-called magic variables.

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Let me give you a quick overview.

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So a magic variable is a special
reserved system variables.

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There's a couple of them, like hostvars,

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which prints all the
variables assigned to a host,

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or groups, which is about all host groups,

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or group_names, which prints
all names of the host groups.

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Or inventory_hostname,

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that is the host name
as defined in inventory.

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Inventory_hostname_short,
the short alternative.

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And there's a couple more,
which you won't see that often.

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Now, you should know that
these metric variables

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are reserved.

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You cannot redefine them yourself.

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They have the highest possible priority.

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Funny story, first time I
encountered magic variables

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was while working with the
playbook to create users.

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And of course I wanted to
define the variable groups.

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That's not going to work

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because of the magic variable groups.

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Can you just imagine that all my users

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were becoming a member of the
groups, as in the host groups?

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That didn't make sense.

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Well, metric variables explain everything.

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So, how do you use them?

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Well, hostvars can be
used to address facts

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or inventory variables from other hosts,

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as in hostvars ansible 2
ansible facts distribution.

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That's something that
you can put in a playbook

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to point to a variable of another host

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in a specific playbook.

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Groups can be used to list all
hosts in an inventory group.

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As in the template, conditional structure

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for host in group web servers.

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We'll see a better example of this

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while discovering templates in
all of the upcoming lessons.

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Group_names has all the
inventory groups a host is in.

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So that is very convenient

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because you can use a
conditional, like here,

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the conditional structure, as
you can see it in a template:

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if 'web servers' in group_names.

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That's going to discover
if a host is a member

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of the group web servers.

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Now inventory_hostname or
inventory_hostname_short

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can be used to address a host

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as alternative to ansible_hostname

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when fact-gathering is disabled.

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So at least it allows you to work with

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hostnames anyway.

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And that's what you need to
know about magic variable.

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Let's continue.