This is a small package I put together quickly to satisfy an immediate need: generating abbreviated URLs in R. As it happens I require this functionality in a couple of projects, so it made sense to have a package to handle the details. It’s not perfect but it does the job. The code is available from github along with vague usage information.
In essence the functionality is simple: first authenticate to shortening service (goo.gl and bitly are supported at present) then shorten or expand URLs as required. The longurl package will perform the latter function too, possibly with greater efficiency.
So, for example, with goo.gl:
shortener_authenticate("86368629146-2ag2qh1j4c26mf5dtm5p7gi85esn3i.apps.googleusercontent.com", "55Y3NsWjiic5Uv8mT-YNMWlK") > shorten.google("http://www.google.com")  "http://goo.gl/MYyLu2" > expand.google("http://goo.gl/MYyLu2")  "http://www.google.com/"
And then doing the same thing with bitly:
> shortener_authenticate("692987373e98473p3fbed10e7c2ea15d6c56fd82", "945d4fe36d8596zap73421090260pfp0d7cbc1a9", "bitly") > shorten.bitly("http://www.google.com")  "http://bit.ly/1Qho4Y5" > expand.bitly("http://bit.ly/1Qho4Y5")  "http://www.google.com/"