Ansible 12. Variables - list variables

The two main ways to define a list variable in YAML (the format used by Ansible) are 

the Block Sequence style and the Flow Sequence (or inline) style.

1) Block Sequence style

1.a) Block Sequence Style (Most Common)

This is the most common and most readable way to define lists, especially for longer lists or complex data structures in Ansible.

Each list item is on a new line and begins with a hyphen and a space (- ).

All list items must be at the same indentation level as the variable name.

📝 Example: Simple List

---

vars:

  # This is a list variable named 'fruits'

  fruits:

    - Apple

    - Orange

    - Banana

    - Grape

The hyphen (-) simply marks the beginning of a new item in the list.

The entire value of each list item is the string itself (Apple, Orange, etc.).

There is no need for a key like name, because the item is the value. 

You would access the first item as fruits[0], which returns the string "Apple"

Each item itself is the value → "Apple", "Orange", etc.

How to refer:

Referring to the Whole List

To refer to the entire fruits list, you use the variable name defined under vars::

• In YAML/Ansible (Jinja2 templating)

The list of fruits is: {{ fruits }} 

# Output: The list of fruits is: ['Apple', 'Orange', 'Banana', 'Grape']

 Accessing Individual Items (Indexing)

Lists are ordered, meaning you can access items by their zero-based index.

• Index 0 refers to the first item (Apple).

• Index 1 refers to the second item (Orange), and so on.

• In YAML/Ansible (Jinja2 templating): You use square brackets [] after the variable name.

My favorite fruit is: {{ fruits[0] }} # 

Output: My favorite fruit is: Apple 

 The last fruit is: {{ fruits[-1] }} # Accessing from the end 

# Output: The last fruit is: Grape

1.b List of Dictionaries: Array of Objects

This defines a list where each item is a key-value pair (a dictionary).

This is often used for defining users, packages, or firewall rules.

📝 Example: Dictionaries: Array of Objects

---

vars:

  users:

    - name: alice

      uid: 1001

    - name: bob

      uid: 1002

    - name: charlie

      uid: 1003

Here each list item is not a single string — it is a dictionary/map with keys:

name    → alice

uid     → 1001

So each element must begin with - followed by a mapping:

Access specific element (index based)

Example: Access Bob’s UID

- debug:
    msg: "{{ users[1].uid }}"

Indexes:

• alice = users[0]

• bob = users[1]

• charlie = users[2]

2) Flow Sequence (or inline) style.

This style is a compact, JSON-like syntax that puts the entire list on a single line. It's often used for short, simple lists.

• The list is enclosed in square brackets ([]).

• Items are separated by a comma and a space (, ).

📝 Example: Simple List (Inline)

---

vars:

  regions: ["east", "west", "north", "south"]

# Or defined in an inventory file:

# [webservers:vars]

# versions = [v1, v2, v3]

📝 Example: Dictionaries: Array of Objects(Inline)

You can also define lists of dictionaries this way, although it sacrifices some readability.

---

vars:

  ports: [ {name: http, num: 80}, {name: https, num: 443} ]

A Single Dictionary variable

vars:

  users:

     name: alice

     uid: 1001

     shell: /bin/bash

✔ Structure:

users = one single dictionary

Keys are: name, uid, shell

✔ Visualization:

users

 ├── name

 ├── uid

 └── shell

✔ You access:

{{ users.name }}

{{ users.shell }}

or

{{ users['name'] }}

Dictionary of Dictionaries

vars:

  users:

    alice:

      uid: 1001

      shell: /bin/bash

      role: admin

    bob:

      uid: 1002

      shell: /bin/zsh

      role: developer

    charlie:

      uid: 1003

      shell: /bin/bash

      role: tester

✔ Visualization:

users

 ├── alice

 │     ├── uid

 │     ├── shell

 │     └── role

 ├── bob

 │     ├── uid

 │     ├── shell

 │     └── role

 └── charlie

       ├── uid

       ├── shell

       └── role

Here:

• users → dictionary

• keys: alice, bob, charlie

• each key contains another dictionary

How to Access Nested Dictionary Values

{{ users.alice.uid }}

{{ users.bob.shell }}

users.alice.uid        # 1001