Can't help with R and related modules, but the answers to your your question re q (and qq, qx & qw) can be found at Quote Like Operators

For information on an arguably "more appropriate use of" backticks, exec, etc, see perldoc -q exec or use perldoc -q backtick from your command line to see a (non-canonical, but very clear) explanation. (Alternately, of course, you can find the same, on-line.)