Script stops working when imported to sage terminal ("plot" not defined)

edit

EDIT: OK, so basically, the Sage command line is not recognizing any sage commands (sqrt, etc) when they are contained in an imported .sage file. It's as if when I import a file to Sage, it doesn't read it using the Sage library. Is there something I have to add to the header of a .sage file for it to be read properly?

Old message:

So everything works fine in the sage notebook, and even if I pretty much rewrite the same commands in the Sage terminal. So it can't be a problem with the script.

But when I copy, paste and save the whole script as a standalone file.sage, and then try

run file.sage

... suddenly:

---> 30 multiPlot = plot(graphs, (x, 0, times[len(times)-1]+3), ymin=0)
    31 
    32 

NameError: name 'plot' is not defined

Why doesn't it read "plot" correctly and expect me to define it?