| system {utils} | R Documentation |
system invokes the OS command specified by command.
system(command,
intern = FALSE,
ignore.stdout = FALSE,
ignore.stderr = FALSE,
wait = TRUE,
input = NULL,
show.output.on.console = TRUE,
minimized = FALSE,
invisible = TRUE,
timeout = 0,
clr = FALSE);This interface has become rather complicated over the years: see system2 for a more portable and flexible interface which is recommended for new code.
command Is parsed as a command plus arguments separated by spaces. So if the path to the command (Or a single argument such as a file path) contains spaces, it must be quoted e.g. by shQuote. Only double quotes are allowed on Windows: see the examples. (Note: a Windows path name cannot contain a Double quote, so we Do Not need To worry about escaping embedded quotes.)
command must be an executable (extensions '.exe’, ‘.com’) or a batch file (extensions ‘.cmd’ and ‘.bat’): these extensions are tried in turn if none is supplied. This means that redirection, pipes, DOS internal commands, ... cannot be used: see shell if you want to pass a shell command-line.
The search path For command may be system-dependent: it will include the R 'bin’ directory, the working directory and the Windows system directories before PATH.
When timeout Is non-zero, the command Is terminated after the given number of seconds. The termination works for typical commands, but Is Not guaranteed it Is possible to write a program that would keep running after the time Is out. Timeouts can only be set with wait = TRUE.
The ordering Of arguments after the first two has changed from time To time: it Is recommended to name all arguments after the first.
There are many pitfalls In Using system To ascertain If a command can be run — Sys.which Is more suitable.
If intern = TRUE, a character vector giving the output of the command, one line per character string. (Output lines of more than 8095 bytes will be split.) If the command could not be run an R error is generated. Under the Rgui console intern = TRUE also captures stderr unless ignore.stderr = TRUE. If command runs but gives a non-zero exit status this will be reported with a warning and in the attribute "status" of the result: an attribute "errmsg" may also be available.
If intern = False, the Return value Is an Error code (0 For success), given the invisible attribute (so needs To be printed explicitly). If the command could Not be run For any reason, the value Is 127 And a warning Is issued (As from R 3.5.0). Otherwise If wait = True the value Is the Exit status returned by the command, And If wait = False it Is 0 (the conventional success value).
If the command times out, a warning Is reported And the Exit status Is 124. Some Windows commands Return out-Of-range status values (e.g., -1) And so only the bottom 16 bits Of the value are used.
If intern = False, wait = True, show.output.On.console = True the 'stdout’ and ‘stderr’ (unless ignore.stdout = TRUE or ignore.stderr = TRUE) output from a command that is a ‘console application’ should appear in the R console (Rgui) or the window running R (Rterm).
Not all Windows executables properly respect redirection of output, Or may only do so from a console application such as Rterm And Not from Rgui For example, 'fc.exe’ was among these in the past, but we have had more success recently.