Powerful replacements for base::system2
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sys

Portable System Utilities

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Powerful replacements for base system2 with consistent behavior across platforms. Supports interruption, background tasks, and full control over STDOUT / STDERR binary or text streams.

Hello World

Run a blocking process

# Blocks until done, interrupt with ESC or CTRL+C
res <- exec_wait("ping", "google.com")

To run as a background process:

# Run as a background process
pid <- exec_background("ping", "google.com")

# Kill it after a while
sleep(4)
tools::pskill(pid)

See the ?sys manual page for details.

Details

The exec_wait function runs a system command and waits for the child process to exit. When the child process completes normally (either success or error) it returns with the program exit code. Otherwise (if the child process gets aborted) R raises an error. The R user can interrupt the program by sending SIGINT (press ESC or CTRL+C) in which case the child process tree is properly terminated. Output streams STDOUT and STDERR are piped back to the parent process and can be sent to a connection or callback function. See the section on Output Streams below for details.

The exec_background function starts the program and immediately returns the PID of the child process. Because this is non-blocking, std_out and std_out can only be TRUE/FALSE or a file path. The state of the process is not controlled by R but the child can be killed manually with [tools::pskill]. This is useful for running a server daemon or background process.

The exec_internal function is a convenience wrapper around exec_wait which automatically captures output streams and raises an error if execution fails. Upon success it returns a list with status code, and raw vectors containing stdout and stderr data (use [rawToChar] for converting to text).

Output Streams:

The std_out and std_err parameters are used to control how output streams of the child are processed. Possible values for both foreground and background processes are:

  • TRUE: print child output in R console
  • FALSE: suppress output stream
  • string: name or path of file to redirect output

In addition the exec_wait function also supports the following std_out and std_err types:

  • connection a writable R [connection] object such as [stdout] or [stderr]
  • function: callback function with one argument accepting a raw vector (use [rawToChar] to convert to text).

When using exec_background with std_out = TRUE or std_err = TRUE on Windows, separate threads are used to print output. This works in RStudio and RTerm but not in RGui because the latter has a custom I/O mechanism. Directing output to a file is usually the safest option.