Bukkit

Welcome only new players:

1. Install this plugin and start the server
2. Stop the server
3. Goto /plugins/ChatBot/
4. Open config.yml
5. Edit variable FirstTime from false to true
6. (This variable represents that players can only welcome player which connects to the server for the first time)
7. Save config.yml
8. Start the server!

Welcome all just connected players:

1. Install this plugin and start the server
2. Stop the server
3. Goto /plugins/ChatBot/
4. Open config.yml
5. Edit variable FirstTime from true to false
6. (This variable represents that players can welcome every player which connects to the server)
7. Save config.yml
8. Start the server!