code: func fullProfileName(profileDir string, proxyHost string) (string, error) {
  	var err error
  	var profileName string
  
  	// If no profile name was passed in, try and extract the active profile from
  	// the ~/.tsh/profile symlink. If one was passed in, append .yaml to name.
  	if proxyHost == "" {
  		profileName, err = os.Readlink(filepath.Join(profileDir, "profile"))
  		if err != nil {
  			return "", trace.ConvertSystemError(err)
  		}
  	} else {
  		profileName = proxyHost + ".yaml"
  	}
  
  	// Make sure the profile requested actually exists.
  	_, err = os.Stat(filepath.Join(profileDir, profileName))
  	if err != nil {
  		return "", trace.ConvertSystemError(err)
  	}
  
  	return profileName, nil
  }
docs: // fullProfileName takes a profile directory and the host the user is trying
  // to connect to and returns the name of the profile file.