R: Invoke a System Command

system2 {base} | R Documentation

## Invoke a System Command

### Description

`system2` invokes the OS command specified by `command`.

### Usage

    system2(command, args = character(),
            stdout = "", stderr = "", stdin = "", input = NULL,
            env = character(), wait = TRUE,
            minimized = FALSE, invisible = TRUE, timeout = 0)

### Arguments

`command` | the system command to be invoked, as a character string.
`args` | a character vector of arguments to `command`.
`stdout, stderr` | where output to ‘stdout’ or ‘stderr’ should be sent. Possible values are `""`, to the R console (the default), `NULL` or `FALSE` (discard output), `TRUE` (capture the output in a character vector) or a character string naming a file.
`stdin` | should input be diverted? `""` means the default, alternatively a character string naming a file. Ignored if `input` is supplied.
`input` | 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.
`env` | character vector of name=value strings to set environment variables.
`wait` | 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 `stdout = TRUE` or `stderr = TRUE`. When running the command asynchronously, no output will be displayed on the `Rgui` console in Windows (it will be dropped, instead).
`timeout` | timeout in seconds, ignored if 0. This is a limit for the elapsed time running `command` in a separate process. Fractions of seconds are ignored.

`minimized` | logical (not `NA`), indicates whether the command window should be displayed initially as a minimized window.
`invisible` | logical (not `NA`), indicates whether the command window should be visible on the screen.

### Details

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`.

### Value

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`.

Some Windows commands return out-of-range status values (e.g., `-1`) and so only the bottom 16 bits of the value are used.

### Note

`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.

### See Also

`system`.

`shell` and `shell.exec`.

[Package base version 4.0.5 Index]