Jinja2 tests

• Testing strings
• Version Comparison
• Group theory tests
• Testing paths
• Task results

Tests in Jinja2 are a way of evaluating template expressions and returning True or False. Jinja2 ships with many of these. See builtin tests in the official Jinja2 template documentation. Tests are very similar to filters and are used mostly the same way, but they can also be used in list processing filters, like C(map()) and C(select()) to choose items in the list.

Like filters, tests always execute on the Ansible controller, not on the target of a task, as they test local data.

In addition to those Jinja2 tests, Ansible supplies a few more and users can easily create their own.

Testing strings

To match strings against a substring or a regex, use the “match” or “search” filter:

vars:
  url: "http://example.com/users/foo/resources/bar"

tasks:
    - shell: "msg='matched pattern 1'"
      when: url | match("http://example.com/users/.*/resources/.*")

    - debug: "msg='matched pattern 2'"
      when: url | search("/users/.*/resources/.*")

    - debug: "msg='matched pattern 3'"
      when: url | search("/users/")

‘match’ requires a complete match in the string, while ‘search’ only requires matching a subset of the string.

Version Comparison

To compare a version number, such as checking if the ansible_distribution_version version is greater than or equal to ‘12.04’, you can use the version_compare filter.

The version_compare filter can also be used to evaluate the ansible_distribution_version:

{{ ansible_distribution_version | version_compare('12.04', '>=') }}

If ansible_distribution_version is greater than or equal to 12, this filter returns True, otherwise False.

The version_compare filter accepts the following operators:

<, lt, <=, le, >, gt, >=, ge, ==, =, eq, !=, <>, ne

This test also accepts a 3rd parameter, strict which defines if strict version parsing should be used. The default is False, but this setting as True uses more strict version parsing:

{{ sample_version_var | version_compare('1.0', operator='lt', strict=True) }}

Group theory tests

To see if a list includes or is included by another list, you can use ‘issubset’ and ‘issuperset’:

vars:
    a: [1,2,3,4,5]
    b: [2,3]
tasks:
    - debug: msg="A includes B"
      when: a|issuperset(b)

    - debug: msg="B is included in A"
      when: b|issubset(a)

Testing paths

The following tests can provide information about a path on the controller:

- debug: msg="path is a directory"
  when: mypath|is_dir

- debug: msg="path is a file"
  when: mypath|is_file

- debug: msg="path is a symlink"
  when: mypath|is_link

- debug: msg="path already exists"
  when: mypath|exists

- debug: msg="path is {{ (mypath|is_abs)|ternary('absolute','relative')}}"

- debug: msg="path is the same file as path2"
  when: mypath|samefile(path2)

- debug: msg="path is a mount"
  when: mypath|ismount

Task results

The following tasks are illustrative of the tests meant to check the status of tasks:

tasks:

  - shell: /usr/bin/foo
    register: result
    ignore_errors: True

  - debug: msg="it failed"
    when: result|failed

  # in most cases you'll want a handler, but if you want to do something right now, this is nice
  - debug: msg="it changed"
    when: result|changed

  - debug: msg="it succeeded in Ansible >= 2.1"
    when: result|succeeded

  - debug: msg="it succeeded"
    when: result|success

  - debug: msg="it was skipped"
    when: result|skipped