title: How can I check for file existence in salt file server
body: <p>I want to copy ssh keys for users automatically, some users do not have keys. </p>
  
  <p>What I have now is:</p>
  
  <pre><code>ssh_auth:                                                                                                                                                                      
    - present                                                                                                                                                                    
    - user: {{ usr }}                                                                                                                                                            
    - source: salt://users/keys/{{usr}}.id_rsa.pub 
  </code></pre>
  
  <p>When a key for a user does not exist on salt:// fileserver, I get an error. Is there some function to check for existence of a file in salt:// fileserver?</p>