How do I check version of R language installed on my system?

There is a version command (not function) in R that provide a fulfilling overview on R environment and version:

> version
               _                           
platform       x86_64-w64-mingw32          
arch           x86_64                      
os             mingw32                     
system         x86_64, mingw32             
status                                     
major          3                           
minor          2.1                         
year           2015                        
month          06                          
day            18                          
svn rev        68531                       
language       R                           
version.string R version 3.2.1 (2015-06-18)
nickname       World-Famous Astronaut

Type R --version at the linux command line.

You can use getRversion() or R.Version()$version.string to show info under R, if you want to check R version from Ubuntu you need to type:

dpkg -s r-base