When working with configuration files in Ansible, we often need to extract specific values to use in subsequent tasks. Let's examine a common scenario with a ZooKeeper configuration file (zoo.cfg) containing:

dataDir=/var/lib/zookeeper
4lw.commands.whitelist=mntr,conf,ruok,stat
syncLimit=2

The initial attempt using regex_search('dataDir.*') has two issues:

- name: Read zoo.cfg content
  shell:
    cmd: cat zoo.cfg
  register: zoo_config_content

- set_fact:
    my_var: "{{ zoo_config_content.stdout | regex_search('dataDir.*')}}"

- name: Print
  debug:
    var: my_var

This captures the entire line (dataDir=/var/lib/zookeeper) rather than just the path value.

To extract only the directory path, we need a more precise regular expression:

- set_fact:
    zk_data_dir: "{{ zoo_config_content.stdout | regex_search('^dataDir=(.*)$', '\\1') | first }}"

Key improvements in this pattern:

• ^ anchors to start of line
• (.*) captures everything after the equals sign
• '\\1' references the first capture group
• | first gets the first match

For simpler cases, the split filter might suffice:

- set_fact:
    zk_data_dir: "{{ (zoo_config_content.stdout | regex_search('^dataDir=.*$')).split('=')[1] }}"

Once stored in a variable, you can reference it in subsequent tasks:

- name: Verify ZooKeeper data directory exists
  file:
    path: "{{ zk_data_dir }}"
    state: directory
    owner: zookeeper
    group: zookeeper
    mode: '0755'

Add validation to handle cases where the value isn't found:

- name: Validate dataDir exists in config
  fail:
    msg: "dataDir not found in zoo.cfg"
  when: zk_data_dir is not defined or zk_data_dir == ""

Here's a full playbook example:

- hosts: zookeeper_servers
  tasks:
    - name: Read zoo.cfg
      command: cat /etc/zookeeper/zoo.cfg
      register: zoo_cfg
      changed_when: false

    - name: Extract dataDir
      set_fact:
        zk_data_dir: "{{ zoo_cfg.stdout | regex_search('^dataDir=(.*)$', '\\1') | first }}"

    - name: Ensure data directory exists
      file:
        path: "{{ zk_data_dir }}"
        state: directory
        owner: zookeeper
        group: zookeeper
        mode: '0755'

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When working with configuration files in Ansible, you often need to extract specific values. Let's examine how to properly use regex_search to extract the dataDir value from a ZooKeeper configuration file.

The current approach has two issues:

  - name: Read zoo.cfg content
    shell:
      cmd: cat zoo.cfg
    register: zoo_config_content

  - set_fact:
      my_var: "{{ zoo_config_content.stdout | regex_search('dataDir.*')}}"

  - name: Print
    debug:
      var: my_var

This returns the entire line (dataDir=/var/lib/zookeeper) rather than just the path we need.

To extract just the directory path, we need a more precise regular expression:

  - set_fact:
      data_dir: "{{ zoo_config_content.stdout | regex_search('dataDir=(.*)', '\\1') | first }}"

This pattern:

• Matches 'dataDir=' literally
• Captures everything after the equals sign in a group
• Uses \\1 to reference the first capture group
• Adds | first to get the first match

Here's a full working example:

- name: Read zoo.cfg content
  ansible.builtin.slurp:
    src: /path/to/zoo.cfg
  register: zoo_config_file

- name: Decode content and extract dataDir
  set_fact:
    zookeeper_data_dir: >-
      {{ (zoo_config_file.content | b64decode) | regex_search('dataDir=([^\\n]*)', '\\1') | first }}

- name: Use the extracted value
  debug:
    msg: "ZooKeeper data directory is set to {{ zookeeper_data_dir }}"

For more complex configuration files, consider these alternatives:

# Using split filter
- set_fact:
    data_dir: "{{ (zoo_config_content.stdout | regex_search('dataDir=.*')).split('=')[1] }}"

# Using lineinfile module (if you need to modify the file)
- name: Get specific line
  lineinfile:
    path: /path/to/zoo.cfg
    state: present
    regexp: '^dataDir='
  register: data_dir_line

- set_fact:
    data_dir: "{{ data_dir_line.line.split('=')[1] }}"

• Use the slurp module instead of shell: cat for better portability
• Handle potential missing values with default filters
• Consider using the ini module for INI-style config files
• Test your regular expressions thoroughly

Here's how you might use this in a role to configure ZooKeeper:

- name: Ensure ZooKeeper data directory exists
  file:
    path: "{{ zookeeper_data_dir }}"
    state: directory
    owner: zookeeper
    group: zookeeper
    mode: '0755'
  when: zookeeper_data_dir is defined