C.12.2. - Output
The output of the subprocess is scanned for x and y values with the new number of points determined by the number of lines of data that are read. If error-bar and/or line-control modes are in effect, corresponding values also are scanned for. It is not considered an error for either of these values to be missing, but those values that are missing from the input are set to 0.
Any line read from the subprocess that doesn't contain valid data is printed on the screen.