You can control mpg123 using the "remote mode", but the "remote" interface is not the same as the "terminal" interface. In fact, the "remote" interface is a bit "primitive" - at least to my way of thinking.

Here's how:

• in terminal 1, enter mpg123 -R --fifo /tmp/mpg123_fifo

• in terminal 2, enter (e.g.) echo "help" > /tmp/mpg123_fifo

• the "remote mode" help menu is output in terminal 1

So yeah - there are things you can do for sure, but those "things" aren't nearly as many as in "terminal" mode. For example, you can't actually "play" a playlist - but oddly, you can "list" the playlist. Playing a song seems to require a one-at-a-time approach; e.g.; from terminal 1:

$ echo "load /home/me/soundfiles/Sinatra-Morning.mp3" > /tmp/mpg123_fifo