If you're stuck with the terminal, but have access to X11 and Java, then I suggest using JavaGraphics` , which allows you to display plots, but continue to work in the terminal. This was also answered hereanswered here, but I learnt it from from JensJens.
If you really want an ASCII plot, I suggest using the Terminal` package that gives you an ASCII plot:
<< Terminal` Plot[Sinc[x], {x, 0, 20}, PlotRange -> All] 
It also works in the front end (although, I don't know why anyone would use it in the FE):
