How to make an item in with_items conditional?

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1

Take this playbook:

  • hosts: mt1-dummys101
    tasks:
  • name: Install apt packages
    sudo: true
    apt: pkg={{ item }}
    with_items:
  • build-essential
  • libyaml-dev
  • python2.7-dev
  • “{{ ‘silversearcher-ag’ if ansible_distribution_major_version == ‘14’ else ‘’ }}”

How would I make it so that silversearcher-ag is installed only on Ubuntu 14 and is omitted for other operating systems?

The above gives:

TASK: [Install apt packages] **************************************************
failed: [mt1-dummys101] => (item=build-essential,libyaml-dev,python2.7-dev,) => {“failed”: true, “item”: “build-essential,libyaml-dev,python2.7-dev,”}
msg: No package matching ‘’ is available

I also tried changing the empty string '' to omit but that also fails:

TASK: [Install apt packages] **************************************************
failed: [mt1-dummys101] => (item=build-essential,libyaml-dev,python2.7-dev,__omit_place_holder__07ef1633a8f8d1dc718ffb780b3f0e54d7f7b02a) => {“failed”: true, “item”: “build-essential,libyaml-dev,python2.7-dev,__omit_place_holder__07ef1633a8f8d1dc718ffb780b3f0e54d7f7b02a”}
msg: No package matching ‘__omit_place_holder__07ef1633a8f8d1dc718ffb780b3f0e54d7f7b02a’ is available

Any way to do this?

2

I’ve done it by having two lists in group vars files and doing a group_by

3

My first thought is to create a new task and use a when clause:

`

  • hosts: mt1-dummys101
    tasks:

  • name: Install apt packages
    sudo: true
    apt: pkg={{ item }}
    with_items:

  • build-essential

  • libyaml-dev

  • python2.7-dev

  • name: Install apt packages for version 14

sudo: true
apt: pkg={{ item }}
with_items: - silversearcher-ag
when: ansible_distribution_major_version == ‘14’

`

4

Yeah, this was what I went with for the time being. I’m curious if there are other ways, but this does seem to be a reasonable solution. Thanks!

5

with_items:
   - "{{ (ansible_distribution_major_version == '14')|ternary(
'silversearcher-ag','' }}"

6

Thanks, but that doesn’t work.

E.g.: I used this slightly tweaked line:

  • “{{ (ansible_distribution_major_version == ‘12’)|ternary(‘silversearcher-ag’, ‘’) }}”

and if the condition is not true, then I get:

TASK: [Install apt packages] **************************************************
failed: [mt1-dummys101] => (item=build-essential,libyaml-dev,python2.7-dev,) => {“failed”: true, “item”: “build-essential,libyaml-dev,python2.7-dev,”}
msg: No package matching ‘’ is available

It seems that for this kind of thing to work, there would either need to be:

  • a way to tell with_items to not add the item at all (by using “omit” perhaps, which doesn’t currently work in this context)
  • “apt” module would ignore a blank string or other sentinel value like “omit”.
7

And I would think the former would be more preferable as it is more generally applicable (would work with all modules).

I think of “with_items” as being analogous to a for loop in most programming languages. So I guess that means the feature that I am wishing I had here is analogous to a “continue” statement in those same programming languages.

8

ah, thought you wanted an empty string, misread from your example.

you'll have to use a when condition or dynamically construct the list,
there is no way to have a list item return a 'delete this item', even
None would return an empty element, but still and element.

list:
- 1
- 2
  - <whatever>

is already a list of 3 items, no value of <whatever> can remove the -
in front of it as it is processed by YAML and <whatever> is by jinja2,
when its already a 3 element list.

example of dynamic list
with_items: {{"[1,2]|union( condition|ternary(['stuff'], ))"}}

it uses union to add elements from either list with 'stuff' or empty
list, which leaves the original 'unchanged'

9

Ah, that’s clever. Probably too clever for me to want to use on my colleagues, but clever nonetheless.

That could be an example if anyone ever writes a book called the “The Little Ansibler” in the style of “The Little Schemer”. :slight_smile: