---
- hosts : 192.168.226.129
  remote_user : root
   vars:
        touch_file : imoocc.file
    task :
       - name : touch file
         shell : "touch /tmp/{{touch_file}}"

ansible-playbook f1.yml --syntax-check
ERROR! Syntax Error while loading YAML.

The error appears to have been in '/etc/ansible/f1.yml': line 4, column 9, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

  remote_user : root
   vars :
        ^ here

exception type: <class 'yaml.scanner.ScannerError'>
exception: mapping values are not allowed here
  in "<unicode string>", line 4, column 9:
       vars :
            ^