There is a bus perhaps 2 if I remember correctly, 2 buses from Santiago to Barcelona - Good News, always start with good news. Now for the bad news, it takes something like nine hours and more if you are forced by timetable considerations to come through Madrid and nine hours on a Spanish bus will result in leg cramps, frozen joints, back pain, your first migraine, over focusing on the bladder and its contents since rest stops are few and far between, in short IF you are still able to walk at the end of the bus ride, you will be a different, changed person. Trains - the good news, no problem there either, the trains in Spain are very comfortable, efficient, run on time and have food service and restrooms on board. Now for the bad news, they are expensive, it will cost almost as much on a train as to fly it - Santiago has a wonderfully small and friendly airport, do consider flying, the difference in price is not that great, more pilgrim friendly, and will save you a visit to your chiropractor or physical therapist when you do return home.