You can install the R ipify package using devtools:
library(devtools)
install_github("gregce/ipify")
library(ipify)
get_ip()## No encoding supplied: defaulting to UTF-8.
## [1] "73.162.222.85"
get_ip(format="json")## $ip
## [1] "73.162.222.85"
get_ip(format="jsonp")## No encoding supplied: defaulting to UTF-8.
## [1] "callback({\"ip\":\"73.162.222.85\"});"