For generic clipboard-reading in Mac, the syntax would be:
indat<-scan(pipe("pbpaste"),what=character(),...)
The ... here is just a place-holder, look up the scan help to see the very many options you have (the scan default is to expect a double variable in the what argument; character is probably safest for generic copy, or you can choose whatever is right for your case).
Similarly, for pasting into the Mac clipboard, the generic Mac syntax is
outdat<-"Hi There!"
cat(outdat, file=pipe("pbcopy","w"), ...)
Note that the nearly the same syntax should work in Windows and Linux as well; you should just replace the pipe calls with the generic connection name "clipboard".
The Kmisc package function mentioned above only works for data frames and tabular data, not for generic copy/paste.