Added on the filter usecase for Ansible

Ansible/README.md

@@ -20,6 +20,8 @@ ansible all -l localhost -m systemd -a "name=nginx state=restarted" -u test --be
 
 `sample.result_list` is a list of lists containing stdout output. We want to filter some numbers from this output. To do this we first filter the correct lines by using the `json_query` filter. If you need to match a specific substring, you could use `select("match", "<regex>")` in combination with the `json_query`. Next we `map` the `regex_search` filter on all lines to extract the data we need. As the `map` filter is a Python generator object, we need to convert it to a list.
 
+The regex `(?<=\()\d+` uses a feature called *positive lookbehind*: `(?<=\()`. It matches a group before the main expression with including it in the result. In this case it matches the opening parantheses `(`. This feature may not be supported in your regex implementation, but in Ansible/Python it is supported. To make the regex even more specific you could add a *positive lookahead* (`(?=\))`) after the `\d+` to match the closing parantheses `)`.
+
 ```yaml
 ---
 
@@ -37,5 +39,5 @@ ansible all -l localhost -m systemd -a "name=nginx state=restarted" -u test --be
 
   tasks:
   - debug:
-      msg: '{{ sample.results | json_query("[*].stdout_lines[1]") | map("regex_search" ,"(?<=\()\d*") | list }}'
+      msg: '{{ sample.results | json_query("[*].stdout_lines[1]") | map("regex_search" ,"(?<=\()\d+") | list }}'
 ```