Plotting line between mouse clicks

[Rex W. <wa...@gm...>]

Hi

I am trying to do this. The user plots any complicated curve.
Then the user clicks at one point (x1,y1) on the graph plot and stores the
value of MOUSE_X and MOUSE_Y in variables x_1 and y_1.
Then the user clicks at another point (x2,y2) on the graph plot and stores
the value of MOUSE_X and MOUSE_Y in variables x_2 and y_2.

I am trying to draw a line segment between the points (x_1,y_1) and
(x_2,y_2).

Is there anyway to do this from the commandline without having to dump the
values of (x_1,y_1) and (x_2,y_2) into a text file in column format and then
re-read it in gnuplot.
I wrote a function my_line(x) = y_1 + ((y_2 - y_1)/(x_2 - x_1))*x and tried
plotting it but it keeps giving me "all points y value undefined!" error.

How do I do this ?

Any help will be appreciated.

Thanks
RW