| system2 | R Documentation |
system2 invokes the OS command specified by command.
system2(command, args = character(),
stdout = "", stderr = "", stdin = "", input = NULL,
env = character(), wait = TRUE,
minimized = FALSE, invisible = TRUE, timeout = 0)
command |
the system command to be invoked, as a character string. |
args |
a character vector of arguments to |
stdout, stderr |
where output to ‘stdout’ or
‘stderr’ should be sent. Possible values are |
stdin |
should input be diverted? |
input |
if a character vector is supplied, this is copied one
string per line to a temporary file, and the standard input of
|
env |
character vector of name=value strings to set environment variables. |
wait |
a logical (not |
timeout |
timeout in seconds, ignored if 0. This is a limit for the
elapsed time running |
minimized, invisible |
arguments that are accepted on Windows but ignored on this platform, with a warning. |
Unlike system, command is always quoted by
shQuote, so it must be a single command without arguments.
For details of how command is found see system.
On Windows, env is only supported for commands such as
R and make which accept environment variables on
their command line.
Some Unix commands (such as some implementations of ls) change
their output if they consider it to be piped or redirected:
stdout = TRUE uses a pipe whereas stdout =
"some_file_name" uses redirection.
Because of the way it is implemented, on a Unix-alike stderr =
TRUE implies stdout = TRUE: a warning is given if this is
not what was specified.
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.
Timeouts cannot be used with interactive commands: the command is run with
standard input redirected from /dev/null and it must not modify
terminal settings. As long as tty tostop option is disabled, which
it usually is by default, the executed command may write to standard
output and standard error.
If stdout = TRUE or stderr = 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. 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.
In other cases, 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 issued and the exit status is
124.
system2 is a more portable and flexible interface than
system. It allows redirection of output without needing
to invoke a shell on Windows, a portable way to set environment
variables for the execution of command, and finer control over
the redirection of stdout and stderr. Conversely,
system (and shell on Windows) allows the invocation of
arbitrary command lines.
There is no guarantee that if stdout and stderr are both
TRUE or the same file that the two streams will be interleaved
in order. This depends on both the buffering used by the command and
the OS.
system.
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