7  System and foreign language interfaces

7.1 Operating system access

Access to the operating system shell is via the R function system. The details will differ by platform (see the on-line help), and about all that can safely be assumed is that the first argument will be a string command that will be passed for execution (not necessarily by a shell) and the second argument will be internal which if true will collect the output of the command into an R character vector.

The functions system.time and proc.time are available for timing (although the information available may be limited on non-Unix-like platforms).

Information from the operating system environment can be accessed and manipulated with

Sys.getenv	OS environment variables
Sys.putenv
Sys.getlocale	System locale
Sys.putlocale
Sys.localeconv
Sys.time	Current time
Sys.timezone	Time zone

A uniform set of file access functions is provided on all platforms:

file.access	Ascertain File Accessibility
file.append	Concatenate files
file.choose	Prompt user for file name
file.copy	Copy files
file.create	Create or truncate a files
file.exists	Test for existence
file.info	Miscellaneous file information
file.remove	remove files
file.rename	rename files
file.show	Display a text file
unlink	Remove files or directories.

There are also functions for manipulating file names and paths in a platform-independent way.

basename	File name without directory
dirname	Directory name
file.path	Construct path to file
path.expand	Expand ~ in Unix path

7.2 Foreign language interfaces

See System and foreign language interfaces in Writing R Extensions for the details of adding functionality to R via compiled code.

Functions .C and .Fortran provide a standard interface to compiled code that has been linked into R, either at build time or via dyn.load. They are primarily intended for compiled C and FORTRAN code respectively, but the .C function can be used with other languages which can generate C interfaces, for example C++.

Functions .Call and .External provide interfaces which allow compiled code (primarily compiled C code) to manipulate R objects.

7.3 .Internal and .Primitive

The .Internal and .Primitive interfaces are used to call C code compiled into R at build time. See .Internal vs .Primitive in R Internals.