Is there a good command-line UNIX charting / graphing / plotting tool out there? I'm looking for something that will plot xy points on an ASCII graph.
Just to clarify, I'm looking for something that will output a graph in ASCII (like ascii-art style), so I can use it over an interactive shell session without needing X.
Try gnuplot. It has very powerful graphing possibilities.
It can output to your terminal in the following way:
gnuplot> set terminal dumb
Terminal type set to 'dumb'
Options are 'feed 79 24'
gnuplot> plot sin(x)
1 ++----------------**---------------+----**-----------+--------**-----++
+ *+ * + * * + sin(x) ****** +
0.8 ++ * * * * * * ++
| * * * * * * |
0.6 ++ * * * * * * ++
* * * * * * * |
0.4 +* * * * * * * ++
|* * * * * * * |
0.2 +* * * * * * * ++
| * * * * * * * |
0 ++* * * * * * *++
| * * * * * * *|
-0.2 ++ * * * * * * *+
| * * * * * * *|
-0.4 ++ * * * * * * *+
| * * * * * * *
-0.6 ++ * * * * * * ++
| * * * * * * |
-0.8 ++ * * * * * * ++
+ * * + * * + * * +
-1 ++-----**---------+----------**----+---------------**+---------------++
-10 -5 0 5 10