Use a default if a variable is not defined

Question

I'm customizing Linux users creation inside my role. I need to let users of my role customize home_directory, group_name, name, password.

I was wondering if there's a more flexible way to cope with default values.

I know that the code below is possible:

- name: Create default
  user:
    name: "default_name"
  when: my_variable is not defined

- name: Create custom
  user:
    name: "{{my_variable}}"
  when: my_variable is defined

But as I mentioned, there's a lot of optional variables and this creates a lot of possibilities.

Is there something like the code above?

- user:
    name: "default_name", "{{my_variable}}"

The code should set name="default_name" when my_variable isn't defined.

I could set all variables on defaults/main.yml and create the user like that:

- name: Create user
  user:
    name: "{{my_variable}}"

But, those variables are inside a really big hash and there are some hashes inside that hash that can't be a default.

related: stackoverflow.com/questions/19614027/…

Ciro Santilli OurBigBook.com
– Ciro Santilli OurBigBook.com

2018-01-08 14:21:07 +00:00
Commented Jan 8, 2018 at 14:21 — Ciro Santilli OurBigBook.com
– Ciro Santilli OurBigBook.com, Commented Jan 8, 2018 at 14:21
docs.ansible.com/ansible/latest/user_guide/…

Simon Logic
– Simon Logic

2022-06-06 11:55:02 +00:00
Commented Jun 6, 2022 at 11:55 — Simon Logic
– Simon Logic, Commented Jun 6, 2022 at 11:55

β.εηοιτ.βε · Accepted Answer · 2024-07-03 10:55:17Z

328

You can use Jinja's default:

- name: Create user
  user:
    name: "{{ my_variable | default('default_value') }}"

edited Jul 3, 2024 at 10:55

β.εηοιτ.βε

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answered Jan 30, 2016 at 22:06

300D7309EF17

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9 Comments

Bernardo Vale Over a year ago

And if the default variable depends upon another variable. For example default('/home/' {{ anothervar }}), is there a way to concatenate those values?

dagonza Over a year ago

Just remove the ' around the default_value and it would use a variable called default_value

Jordan Stewart Over a year ago

Doesn't work if variable is nested like {{ dict.key | default(5) }}. It will fail if dict is undefined.

Roman Kruglov Over a year ago

@JordanStewart I had the same case - with nested variables. I posted an answer with possible solutions below.

svcabre Over a year ago

@BernardoVale if the default variable depends from another variable. As on your example default('/home/' {{ anothervar }}). I had to do the following to get it to work with for example a path construction: {{ my_variable | default('/opt/'+ another_var_dir) }}

|

Roman Kruglov · Accepted Answer · 2019-07-10 15:47:57Z

17

If anybody is looking for an option which handles nested variables, there are several such options in this github issue.

In short, you need to use "default" filter for every level of nested vars. For a variable "a.nested.var" it would look like:

- hosts: 'localhost'
  tasks:
    - debug:
        msg: "{{ ((a | default({})).nested | default({}) ).var | default('bar') }}"

or you could set default values of empty dicts for each level of vars, maybe using "combine" filter. Or use "json_query" filter. But the option I chose seems simpler to me if you have only one level of nesting.

edited Jul 10, 2019 at 15:47

answered Jul 10, 2019 at 14:25

Roman Kruglov

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Comments

Tommy Nguyen · Accepted Answer · 2017-08-14 09:54:58Z

16

Not totally related, but you can also check for both undefined AND empty (for e.g my_variable:) variable. (NOTE: only works with ansible version > 1.9, see: link)

- name: Create user
  user:
    name: "{{ ((my_variable == None) | ternary('default_value', my_variable)) \
    if my_variable is defined else 'default_value' }}"

edited Aug 14, 2017 at 9:54

answered Aug 14, 2017 at 9:15

Tommy Nguyen

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1 Comment

eagle33322 Over a year ago

This is great, very useful.

panticz · Accepted Answer · 2019-03-26 09:09:44Z

7

In case you using lookup to set default read from environment you have also set the second parameter of default to true:

- set_facts:
    ansible_ssh_user: "{{ lookup('env', 'SSH_USER') | default('foo', true) }}"

You can also concatenate multiple default definitions:

- set_facts:
    ansible_ssh_user: "{{ some_var.split('-')[1] | default(lookup('env','USER'), true) | default('foo') }}"

answered Mar 26, 2019 at 9:09

panticz

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Comments

Samselvaprabu · Accepted Answer · 2020-03-10 13:57:56Z

7

If you are assigning default value for boolean fact then ensure that no quotes is used inside default().

- name: create bool default
  set_fact:
    name: "{{ my_bool | default(true) }}"

For other variables used the same method given in verified answer.

- name: Create user
  user:
    name: "{{ my_variable | default('default_value') }}"

answered Mar 10, 2020 at 13:57

Samselvaprabu

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Comments

Jack · Accepted Answer · 2017-05-18 22:24:23Z

If you have a single play that you want to loop over the items, define that list in group_vars/all or somewhere else that makes sense:

all_items:
  - first
  - second
  - third
  - fourth

Then your task can look like this:

  - name: List items or default list
    debug:
      var: item
    with_items: "{{ varlist | default(all_items) }}"

Pass in varlist as a JSON array:

ansible-playbook <playbook_name> --extra-vars='{"varlist": [first,third]}'

Prior to that, you might also want a task that checks that each item in varlist is also in all_items:

  - name: Ensure passed variables are in all_items
    fail:
      msg: "{{ item }} not  in all_items list"
    when: item not in all_items
    with_items: "{{ varlist | default(all_items) }}"

pshunter · Accepted Answer · 2019-09-12 15:48:21Z

4

The question is quite old, but what about:

- hosts: 'localhost'
  tasks:
    - debug:
        msg: "{{ ( a | default({})).get('nested', {}).get('var','bar') }}"

It looks less cumbersome to me...

answered Sep 12, 2019 at 15:48

pshunter

716 bronze badges

1 Comment

reinierpost Over a year ago

The problem is you need to repeat this wherever the variable is used. The question is how to set a default once and for all.

Juuso Ohtonen · Accepted Answer · 2023-02-15 07:24:30Z

0

@Roman Kruglov mentioned json_query. It's perfect for nested queries.

An example of json_query sample playbook for existing and non-existing value:

- hosts: localhost
  gather_facts: False
  vars:
    level1:
      level2:
        level3:
          level4: "LEVEL4"
  tasks:
    - name: Print on existing level4
      debug:
         var: level1 | json_query('level2.level3.level4')  # prints 'LEVEL4'
      when: level1 | json_query('level2.level3.level4')

    - name: Skip on inexistent level5
      debug:
         var: level1 | json_query('level2.level3.level4.level5')  # skipped
      when: level1 | json_query('level2.level3.level4.level5')

answered Feb 15, 2023 at 7:24

Juuso Ohtonen

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Comments

Raoul Scarazzini · Accepted Answer · 2023-02-21 08:13:54Z

0

You can also use an if statement:

# Firewall manager: firewalld or ufw
firewall: "{{ 'firewalld' if ansible_os_family == 'RedHat' else 'ufw' }}"

answered Feb 21, 2023 at 8:13

Raoul Scarazzini

1

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