anchor.diff:  If a server is already running, the command only displays the server's PID. A new server will not be started.
   
   ```console
  -% rubocop --start-server
  +$ rubocop --start-server
   RuboCop server (16060) is already running.
   ```
   
   The server process name is basically `rubocop --server` and the project directory path:
   
   ```console
  -% ps aux | grep 'rubocop --server'
  +$ ps aux | grep 'rubocop --server'
   user             16060   0.0  0.0  5078568   2264   ??  S     7:54AM   0:00.00 rubocop --server /Users/user/src/github.com/rubocop/rubocop
   user             16337   0.0  0.0  5331560   2396   ??  S    23:51PM   0:00.00 rubocop --server /Users/user/src/github.com/rubocop/rubocop-rails
   ```
  
positive.code: 
  These are the command-line options for server operations:
  
  * `--server` ... If a server process has not been started yet, start the
  server process and execute inspection with server. You can specify
  the server host and port with the `$RUBOCOP_SERVER_HOST` and
  the `$RUBOCOP_SERVER_PORT` environment variables.
  * `--no-server` ... If a server process has been started, stop the
  server process and execute inspection without the server.
  * `--restart-server` ... Restart server process.
  * `--start-server` ... Start server process.
  * `--stop-server` ... Stop server process.
  * `--server-status` ... Show server status.
  
  == Environment Variables
  
  
negative.code: The following is an example:
  
  ```console
  $ RUBOCOP_SERVER_PORT=98989 rubocop --start-server
  ```
  