N.B.—use of
plot '-' ; ... ; replot
is not recommended—gnuplot does not store the inline data internally. Since replot appends new information to the previous plot and then executes the modified command, the '-' will ask once more for the data. '-' is intended for situations where it is useful to have data and commands together, e.g., when gnuplot is run as a sub-process of some front-end application. Some of the demos, for example, might use this feature.
A blank filename ('') specifies that the previous filename should be reused. This can be useful with things like
plot 'a/very/very/long/filename' using 1:2, '' using 1:3, '' using 1:4
On some computer systems with a popen function (Unix), the datafile can be piped through a shell command by starting the file name with a '<'. For example
pop(x) = 103*exp(-x/10) plot "< awk '{print $1-1965, $2}' population.dat", pop(x)
would plot the same information as the first population example but with years since 1965 as the x axis. If you want to execute this example, you have to delete all comments from the data file above or substitute the following command for the first part of the command above (the part up to the comma):
plot "< awk '$0 !~ /^#/ {print $1-1965, $2}' population.dat"
While this approach is most flexible, it is possible to achieve simple filtering with the using or thru keywords.