Ansible – Modify and join a list

So you have a list with a number of item which are the /data* path where you want to put your hadoop hdfs data and you want to add after each item the end of the path mount point, here is a solution.

- hosts: localhost
  vars:
    hadoop_dir_hdfs_data: "/hadoop/hdfs/data"
    hadoop_dir:
      - "/data1"
      - "/data2"
      - "/data3"
      - "/data4"
      - "/data5"
  tasks:
  - set_fact:
      my_result: "{{ hadoop_dir | map('regex_replace', '(.*)', '\\1' + hadoop_dir_hdfs_data) | join(',') }}"
  - debug:
      var: my_result

This will give you this output

TASK [debug] ****************************************************************************************************************************
ok: [localhost] => {
    "my_result": "/data1/hadoop/hdfs/data,/data2/hadoop/hdfs/data,/data3/hadoop/hdfs/data,/data4/hadoop/hdfs/data,/data5/hadoop/hdfs/data"
}

Explanation :

• I apply a map filter on the hadoop_dir list : map(‘regex_replace’
• This map filter use regex_replace on the list searching anything and capture this anything : (.*)
• I concatenate the first matching member (there is only one member here) with the hadoop_dir_hdfs_data : ‘\\1’ + hadoop_dir_hdfs_data
• I join all the items from my list with a ‘,’ : join(‘,’)