Is there a package to process command line options in R?

Is there a package to process command-line options in R? I know `commandArgs`, but it's too basic. Its result is basically the equivalent to `argc` and `argv` in `C`, but I'd need something on top of that, just like `boost::program_options` in `C++`, or `GetOptions::Long` in `perl`. In particular, I'd like to specify in advance what options are allowed and give an error message if the user specifies something else. The call would be like this (with user options --width=32 --file=foo.txt): ``` R --vanilla --args --width=32 --file=foo.txt < myscript.R ``` or, if `Rscript` is used: ``` myscript.R --width=32 --file=foo.txt ``` (Please don't say, "why don't you write it yourself, it's not that hard". In other languages you don't have to write it yourself either. :)