Imagine a New York subway-MTA map that would include a line running to Albany and it gives you a sense of where this train line stands.
The R3 line of Rodalies de Barcelona, the commuter rail and metro service for Barcelona metropolitan area, runs all the way from Latour de Carol (La Tor de Querol in Catalan) to Barcelona...(end of the line in top right corner of the map).
If you travel from Toulouse to Barcelona, it is a scenic if longer (yet cheaper, at most half price from faster route) alternative through the Pyrenees.
You can book first leg from Toulouse to Latour de Carol-Enveitg (3 hours trip) via SNCF ... Tickets for R3 part can only be purchased I believe in train stations...
Daily, 4 R3 trains run from Barcelona (6:27, 9:56, 12:38, 15:06) and 5 R3 trains from Latour de Carol to Barcelona (8:50, 10:48, 13:34, 17:13, 18:52) ...Trip takes a little over 3 hours.
I plan to try that route mid-July.