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regexansible

Append to a line only if regexp is found

I have the following Ansible code:

---
- name: skip fail2ban in iptables checkmk plugin
  hosts: localhost
  gather_facts: no
  tasks:
    - name: modify plugin
      ansible.builtin.lineinfile:
        path: /usr/lib/check_mk_agent/plugins/mk_iptables
        backrefs: True
        regexp: '^(iptables-save.*)'
        line: '\1 | grep -v "f2b"'

What I want here is to append | grep -v "f2b" to the line that starts by iptables-save in a bash script. This works fine.

However, I would like to make it so that if the grep function was already added, don't add it again. So I try some sort of ^(iptables-save.*)(?[grep]) which I had no luck with, probably because I misunderstand

  1. how to correctly exclude a pattern within a regexp and
  2. it seems like lineinfile will still append to EOF if no matches are found.

How can I get around this?

Solution

  • Q: "How to correctly exclude a pattern within a regexp?"

    For a test file mk_iptables with content of

    START
iptables-save foo bar
END

    a minimal example playbook

    ---
- hosts: localhost
  become: False
  gather_facts: False

  tasks:

    - name: modify plugin
      ansible.builtin.lineinfile:
        path: mk_iptables
        backrefs: True
        regexp: '^(iptables-save.*)(?<!"f2b")$'
        line: '\1 | grep -v "f2b"'
      diff: True

    will result into an output of

    TASK [modify plugin] *****************
--- before: mk_iptables (content)
+++ after: mk_iptables (content)
@@ -1,3 +1,3 @@
 START
-iptables-save foo bar
+iptables-save foo bar | grep -v "f2b"
 END

    for the first run and for the second

    TASK [modify plugin] *****************
ok: [localhost]

    as well a test file content of

    cat mk_iptables
START
iptables-save foo bar | grep -v "f2b"
END

    Credits To