When the show command is used to display a message on the squeezebox remote, the command never completes.  After send the command "00:04:20:17:c6:4a show line1:test", I receive no reply from the server.  It appears that the show command is asynchronous and that the Display object is responsible for running a callback when the showBriefly method completes.  The NoDisplay class, which is used on for squeezebox receivers, overrides showBriefly and does not call the callback.  

I have attached the relevant log entries from the my test.

[13-01-06 15:18:13.6530] Slim::Plugin::CLI::Plugin::client_socket_read (346) 192.168.1.117:57758 - Buffered [68%3Aa8%3A6d%3Ab0%3A30%3A8e show line1:test
]
[13-01-06 15:18:13.6536] Slim::Plugin::CLI::Plugin::client_socket_buf_parse (385) 192.168.1.117:57758
[13-01-06 15:18:13.6544] Slim::Plugin::CLI::Plugin::client_socket_buf_parse (408) Using terminator "\r\n" for 192.168.1.117:57758
[13-01-06 15:18:13.6550] Slim::Plugin::CLI::Plugin::cli_process (529) 68%3Aa8%3A6d%3Ab0%3A30%3A8e show line1:test
[13-01-06 15:18:13.6557] Slim::Plugin::CLI::Plugin::cli_process (553) Parsing command: Found client [68:a8:6d:b0:30:8e]
[13-01-06 15:18:13.6565] Slim::Plugin::CLI::Plugin::cli_process (611) Processing request [show]
[13-01-06 15:18:13.6567] Slim::Plugin::CLI::Plugin::cli_process (645) Dispatching [show]
[13-01-06 15:18:13.6570] Slim::Display::NoDisplay::showBriefly (34) caller Slim::Control::Commands::showCommand (1884) notifyLevel=1 
[13-01-06 15:18:13.6574] Slim::Plugin::CLI::Plugin::cli_process (660) Request [show] is async: will be back