UNIX-like "cut" command in R

On Mon, 2 May 2011, P Ehlers wrote:

Use str_sub() in the stringr package:

require(stringr)  # install first if necessary
s <- "abcdefghijklmnopqrstuvwxyz"

str_sub(s, c(1,12,17), c(3,15,-1))
#[1] "abc"        "lmno"       "qrstuvwxyz"

Thanks.  That's very close to what I'm looking for, but it seems to 
correspond to "cut -c", not to "cut -f".  Can it work with delimiters 
or only with character counts?

Mike