By passing the file argument to the postscript() device driver function, you may store the graphics in PostScript format in a file of your choice. The plot will be in portrait orientation unless the horizontal=T argument is given, and you can control the size of the graphic with the width and height arguments (the plot will be scaled as appropriate to fit these dimensions.) For example, the command
postscript("file.ps", height=4)
will produce a file containing PostScript code for a figure 4 inches
high, perhaps for inclusion in a document. 
It is important to note that
if the file named in the command already exists, it will be overwritten.
This is the case even if the file was only created earlier in the same S
session.