这是shell命令。在shell里面写

shell是linux系统自带的吗？我没用过，能详细说一下吗？谢谢

可以写到终端上。
The shell is the program which actually processes commands and returns output. Most shells also manage foreground and background processes, command history and command line editing. These features (and many more) are standard in bash, the most common shell in modern linux systems.
http://superuser.com/questions/144666/what-is-the-difference-between-shell-console-and-terminal

It is the command line version of R, usually under Linux/Unix system, in windows, you also could utilize the same command if you do not want to use GUI (Graphical User Interface).

谢谢两位的指导，长知识了