How to Insert a new string into telegraf.conf's inputs.ping using ansible regexp - regex

Question

I'm trying to use ansible to update telegraf.conf's [[inputs.ping]].
telegraf.conf looks like the following:
[[inputs.ping]]
urls = ["tac-temp1","tac-temp2", "tac-temp3","tac-temp4"] #tac
count = 30
timeout = 15.0
[inputs.ping.tags]
name = "tac"
[[inputs.ping]]
urls = ["prod-temp1","prod-temp2", "prod-temp3","prod-temp4"] #prod
count = 30
timeout = 15.0
[inputs.ping.tags]
name = "prod"
[[inputs.ping]]
urls = ["test-temp1","test-temp2", "test-temp3","test-temp4"] #test
count = 30
timeout = 15.0
[inputs.ping.tags]
name = "test"
I'm trying to add ,"tac-temp10" after ,"tac-temp4" in line 2 shown above.
- hosts: Servers
become: yes
become_method: sudo
tasks:
- name: Loading telegraf.conf content for search
shell: cat /tmp/telegraf.conf
register: tele_lookup
- name: Adding Server to /tmp/telegraf.conf if does not exists
lineinfile:
path: /tmp/telegraf.conf
state: present
regexp: '^((.*)"] #tac$)'
line: ',"tac-temp10"'
backup: yes
when: tele_lookup.stdout.find('tac-temp10') != '0'
regexp: '^((.*)"] #tac$)' is replacing the whole line with ,"tac-temp10". Expected output:
[[inputs.ping]]
urls = ["tac-temp1","tac-temp2", "tac-temp3","tac-temp4","tac-temp10"] #tac
count = 30
timeout = 15.0
[inputs.ping.tags]
name = "tac"

Answer 1

Warning: Ugly regexp ahead. Beware of unpredictable understanding for next guys (including you after time passed by...) doing maintenance.
The following will add your server at the end of the list if it is not already present (anywhere in the list) with a single idempotent task.
- name: add our server if needed
lineinfile:
path: /tmp/test.conf
backup: yes
state: present
regexp: '^( *urls *= *\[)(("(?!tac-temp10)([a-zA-Z0-9_-]*)",? *)*)(\] #tac)$'
backrefs: yes
line: '\1\2, "tac-temp10"\5'
You need to use backreferences to put back on the line the already matched parts of the expression. I used backup: yes so I could easily come back to the original for my tests. Feel free to drop it.
As you can see (and as advised in my warning) this is pretty much impossible to understand for anyone having to quickly read the code. If you have to do anything more fancy/complicated, consider using a template and storing your server list in a variable somewhere.