Problem scenario
You want to see if an Ansible playbook is injecting (or leaving) two braces, "{{" or "}}", in a specific file on Linux. These symbols can be injected accidentally with little notification. Variable substitution could fail during the course of a playbook run. This is a subtle problem that may have no alert. You want some debugging to check for these symbols. How do you know a file on a managed node does not have a "{{" or "}}"?
Solution
Root cause
What makes the double braces difficult to place into a shell module in Ansible is that Ansible views them (as a pair) as a reserved symbol; variable expansion in Ansible is done via these very symbols in quotes.
Procedure
You need to re-write the playbook to use the "shell" module. To search for lines that have both types of double braces, "{{" and "}}", with no quotes, put these two lines in your playbook.shell: /usr/bin/cat /path/to/file.txt | grep "\{\{" | grep "\}\}"
register: foundplaceholder
The backslash "\" (without quotes) acts as an escape character. The variable foundplaceholder will have a value if a single line had both types of double braces, "{{" and "}}" (with no quotes).