Need to generate a list based on one item name and number of items

Question

I have two variables:

name: "abc232323defg10"
cycle: "4"

I need to generate a list:

list:
  - abc232323defg10
  - abc232323defg9
  - abc232323defg8
  - abc232323defg7

where:

abc232323defg9 = abc232323defg(10-(cycle-3)),
abc232323defg8 = abc232323defg(10-(cycle-2)), 
abc232323defg7 = abc232323defg(10-(cycle-1))

The variable "cycle" is the same as the number of items in the list, and I already have item where last 2 characters are the "largest number" (that is number 10 in the example). So other items should have last two characters subtracted from this "largest number" (with increments for each cycle). Cycle is never bigger then "largest number", but can be equal. Order in the list is not relevant.

PS last two characters can be any number or even combination of one letter (a-z,A-Z) and one number. So it can be t1, or e9, or 88... that is why I think I need regex.

Any idea?

Answer 1

Given the variables

  _name: "abc232323defg10"
  cycle: "4"

Declare the variables prefix and index by splitting _name

  prefix: "{{ _name|regex_replace('^(.+?)(\\d+)$', '\\1') }}"
  index: "{{ _name|regex_replace('^(.+?)(\\d+)$', '\\2') }}"

give

  prefix: abc232323defg
  index: 10

Declare the list indexes

 indexes: "{{ query('sequence', params) }}"
 params: "start={{ index|int }} end={{ index|int - cycle|int + 1 }} stride=-1"

give

  indexes: ['10', '9', '8', '7']

Finally, create product of the prefix and indexes, and join them

  names: "{{ [prefix]|product(indexes)|map('join')|list }}"

gives the expected result

  names:
    - abc232323defg10
    - abc232323defg9
    - abc232323defg8
    - abc232323defg7

---

Example of a complete playbook for testing

- hosts: localhost

  vars:

    _name: "abc232323defg10"
    cycle: "4"

    prefix: "{{ _name|regex_replace('^(.+?)(\\d+)$', '\\1') }}"
    index: "{{ _name|regex_replace('^(.+?)(\\d+)$', '\\2') }}"
    indexes: "{{ query('sequence', params) }}"
    params: "start={{ index|int }} end={{ index|int - cycle|int + 1 }} stride=-1"
    names: "{{ [prefix]|product(indexes)|map('join')|list }}"

  tasks:

    - debug:
        msg: |
          prefix: {{ prefix }}
          index: {{ index }}
          indexes: {{ indexes }}
          names:
            {{ names|to_nice_yaml|indent(2) }}