a character string giving the name of the file.
If it is of the form "|cmd", the output is piped to the command given by cmd.
If it is NULL, then no external file is created (effectively, no drawing occurs),
but the device may still be queried (e.g., for size of text). For use with onefile = FALSE
give a C integer format such as "Rplot%03d.pdf" (the default in that case)
plot
ggplot or list of ggplots to save, defaults to last plot displayed
...
other arguments passed on to graphics device
Details
default output is to create one pdf regardless of size of list of plots inputted