I believe the play command is part of the sox install.
I installed sox, but now it refuses to play mp3s...something like "Failed reading blablabla.mp3 Do not understand format type: mp3"
On my system I ran "sox -h" to show the supported file formats. mp3 wasn't one of them. However, doing a "man sox" I see: .mp3 MP3 Compressed Audio MP3 audio files come from the MPEG standards for audio and video compression. They are a lossy compression format that achieves good compression rates with a minimum amount of quality loss. Also see Ogg Vorbis for a similar format. MP3 support in SoX is optional and requires access to either or both the external libmad and libmp3lame libraries. To see if there is support for Mp3 run sox -h and look for it under the list of supported file formats as "mp3". -- Marshall Lake -- mlake@mlake.net -- http://mlake.net