system invokes the OS command specified by
system(command, intern = FALSE, ignore.stdout = FALSE, ignore.stderr = FALSE, wait = TRUE, input = NULL, show.output.on.console = TRUE, minimized = FALSE, invisible = TRUE)
the system command to be invoked, as a character string.
a logical (not
NA) which indicates whether to
capture the output of the command as an R character vector.
a logical (not
indicating whether messages written to
stderr should be ignored.
a logical (not
NA) indicating whether the R
interpreter should wait for the command to finish, or run it
asynchronously. This will be ignored (and the interpreter will
always wait) if
intern = TRUE.
if a character vector is supplied, this is copied one
string per line to a temporary file, and the standard input of
command is redirected to the file.
arguments that are accepted on Windows but ignored on this platform, with a warning.
whether to capture the output of the command and show it on the R
console (not used by
Rterm, which shows the output in the
wait is false).
NA), indicates whether a
command window should be displayed initially as a minimized window.
NA), indicates whether a
command window should be visible on the screen.
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.
intern = TRUE also captures
ignore.stderr = TRUE.
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
intern = FALSE, the return value is an error code (
for success), given the invisible attribute (so needs to be printed
explicitly). If the command could not be run for any reason, the
127. 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).
Some Windows commands return out-of-range status values
-1) and so only the bottom 16 bits of the value are used.
intern = FALSE, wait = TRUE, show.output.on.console = TRUE the
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 (
Not all Windows executables properly respect redirection of output, or
may only do so from a console application such as
Rterm and not
Rgui: for example,
fc.exe was among these in the past,
but we have had more success recently.
For command-line R, error messages written to
stderr will be
sent to the terminal unless
ignore.stderr = TRUE. They can be
captured (in the most likely shells) by
system("some command 2>&1", intern = TRUE)
For GUIs, what happens to output sent to
intern = FALSE is interface-specific, and it
is unsafe to assume that such messages will appear on a GUI console
(they do on the macOS GUI's console, but not on some others).
Precisely what is seen by the user depends on the optional parameters,
Rterm is being used, and whether a
console command or GUI application is run by the command.
By default nothing will be seen in either front-end until the command finishes and the output is displayed.
For console commands
Rgui will open a new ‘console’, so
invisible = FALSE, a commands window will appear for the
duration of the command. For
Rterm a separate commands window
will appear for console applications only if
wait = FALSE and
invisible = FALSE.
GUI applications will not display in either front-end unless
invisible is false.
It is possible to interrupt a running command being waited for from
the keyboard (using the Esc key in
Rgui or Ctrl-C
Rterm) or from the
Rgui menu: this should at least
return control to the R console. R will attempt to shut down the
process cleanly, but may need to force it to terminate, with the
possibility of losing unsaved work, etc.
Do not try to run console applications that require user
intern = TRUE or
show.output.on.console = TRUE. They will not work.
How processes are launched differs fundamentally between Windows and
Unix-alike operating systems, as do the higher-level OS functions on
which this R function is built. So it should not be surprising that
there are many differences between OSes in how
For the benefit of programmers, the more important ones are summarized
in this section.
The most important difference is that on a Unix-alike
system launches a shell which then runs
Windows the command is run directly -- use
shell for an
interface which runs
command via a shell (by default
the Windows shell
cmd.exe, which has many differences from
a POSIX shell).
This means that it cannot be assumed that redirection or piping will
system (redirection sometimes does, but we have seen
cases where it stopped working after a Windows security patch), and
shell) must be used on Windows.
What happens to
stderr when not
captured depends on how R is running: Windows batch commands behave
like a Unix-alike, but from the Windows GUI they are
system(intern = TRUE) captures
when run from the Windows GUI console unless
The behaviour on error is different in subtle ways (and has differed between R versions).
The quoting conventions for
command differ, but
shQuote is a portable interface.
invisible only do something on Windows (and are most relevant
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
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
.com) or a batch file (extensions
these extensions are tried in turn if none is supplied.) This means
that redirection, pipes, DOS internal commands, … cannot be used:
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
Unix-alikes pass the command line to a shell (normally
and POSIX requires that shell), so
command can be anything the
shell regards as executable, including shell scripts, and it can
contain multiple commands separated by
system does not use a shell and there is a separate
shell which passes command lines to a shell.
popen is used to invoke the
command and the output collected, line by line, into an R
character vector. If
the C function
system is used to invoke the command.
wait is implemented by appending
& to the command: this
is in principle shell-dependent, but required by POSIX and so widely
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.
.Platform for platform-specific variables.
pipe to set up a pipe connection.
# list all files in the current directory using the -F flag system("ls -F") # t1 is a character vector, each element giving a line of output from who # (if the platform has who) t1 <- try(system("who", intern = TRUE)) try(system("ls fizzlipuzzli", intern = TRUE, ignore.stderr = TRUE)) # zero-length result since file does not exist, and will give warning.
Run the code above in your browser using DataCamp Workspace