ffmpeg

install ffmpeg
apt-get install ffmpeg
 
 Convert .wav file to mp3 
 ffmpeg -i track01.wav -acodec mp3 track01.mp3
 
 You can also specify the bitrate of the MP3 with the -ab flag. 
 ffmpeg -i track01.wav -acodec mp3 -ab 64k track01.mp3
 
 Convert a folder full of .wav into .mp3 
 for i in *.wav; do ffmpeg -i "$i" -acodec mp3 -ab 64k "$(basename "$i" .wav)".mp3 ; done