Mp3info

get/set mp3 id-tags

get tags

mp3info -x *.mp3

set tags

mp3info -i -a <ARTIST> -l <ALBUM-NAME> -t "<TITLE of TRACK>" file.mp3

or cd to dir and loop through:

for f in *.mp3; do
   # ...
   # do some shit here to grab artist/album/title from filename ...
   # ...
   mp3info -i -a <ARTIST> -l <ALBUM-NAME> -t "$f" "$f"
done