splitting a string by space except when contained within quotes

I've been trying to split a space delimited string with double-quotes in R
for some time but without success. An example of a string is as follows:

/rainfall snowfall "Channel storage" "Rivulet storage"/

It's important for us because these are column headings that must match the
subsequent data.

Here is some code I've been trying:

str <- 'rainfall snowfall "Channel storage" "Rivulet storage"'
regex <- "[^\\s\"']+|\"([^\"]*)\""
split <- strsplit(str, regex, perl=T)
what I would like is

[1] "rainfall" "snowfall" "Channel storage" "Rivulet storage"

but what I get is:

[1] ""  " " " " " "

The vector is the right length (which is encouraging) but of course the
strings are empty or contain a single space. Any suggestions?

scan(con <- textConnection(str), what = "")

close(con)