run: Run external command, and wait until finishes

Description

run provides an interface similar to base::system() and base::system2(), but based on the process class. This allows some extra features, see below.

Usage

run(
  command = NULL,
  args = character(),
  error_on_status = TRUE,
  wd = NULL,
  echo_cmd = FALSE,
  echo = FALSE,
  spinner = FALSE,
  timeout = Inf,
  stdout = "|",
  stderr = "|",
  stdout_line_callback = NULL,
  stdout_callback = NULL,
  stderr_line_callback = NULL,
  stderr_callback = NULL,
  stderr_to_stdout = FALSE,
  env = NULL,
  windows_verbatim_args = FALSE,
  windows_hide_window = FALSE,
  encoding = "",
  cleanup_tree = FALSE,
  ...
)

Value

A list with components:

status The exit status of the process. If this is NA, then the process was killed and had no exit status.
stdout The standard output of the command, in a character scalar.
stderr The standard error of the command, in a character scalar.
timeout Whether the process was killed because of a timeout.

Arguments

command: Character scalar, the command to run. If you are running .bat or .cmd files on Windows, make sure you read the 'Batch files' section in the process manual page.
args: Character vector, arguments to the command.
error_on_status: Whether to throw an error if the command returns with a non-zero status, or it is interrupted. The error classes are system_command_status_error and system_command_timeout_error, respectively, and both errors have class system_command_error as well. See also "Error conditions" below.
wd: Working directory of the process. If NULL, the current working directory is used.
echo_cmd: Whether to print the command to run to the screen.
echo: Whether to print the standard output and error to the screen. Note that the order of the standard output and error lines are not necessarily correct, as standard output is typically buffered. If the standard output and/or error is redirected to a file or they are ignored, then they also not echoed.
spinner: Whether to show a reassuring spinner while the process is running.
timeout: Timeout for the process, in seconds, or as a difftime object. If it is not finished before this, it will be killed.
stdout: What to do with the standard output. By default it is collected in the result, and you can also use the stdout_line_callback and stdout_callback arguments to pass callbacks for output. If it is the empty string (""), then the child process inherits the standard output stream of the R process. (If the main R process does not have a standard output stream, e.g. in RGui on Windows, then an error is thrown.) If it is NULL, then standard output is discarded. If it is a string other than "|" and "", then it is taken as a file name and the output is redirected to this file.
stderr: What to do with the standard error. By default it is collected in the result, and you can also use the stderr_line_callback and stderr_callback arguments to pass callbacks for output. If it is the empty string (""), then the child process inherits the standard error stream of the R process. (If the main R process does not have a standard error stream, e.g. in RGui on Windows, then an error is thrown.) If it is NULL, then standard error is discarded. If it is a string other than "|" and "", then it is taken as a file name and the standard error is redirected to this file.
stdout_line_callback: NULL, or a function to call for every line of the standard output. See stdout_callback and also more below.
stdout_callback: NULL, or a function to call for every chunk of the standard output. A chunk can be as small as a single character. At most one of stdout_line_callback and stdout_callback can be non-NULL.
stderr_line_callback: NULL, or a function to call for every line of the standard error. See stderr_callback and also more below.
stderr_callback: NULL, or a function to call for every chunk of the standard error. A chunk can be as small as a single character. At most one of stderr_line_callback and stderr_callback can be non-NULL.
stderr_to_stdout: Whether to redirect the standard error to the standard output. Specifying TRUE here will keep both in the standard output, correctly interleaved. However, it is not possible to deduce where pieces of the output were coming from. If this is TRUE, the standard error callbacks (if any) are never called.
env: Environment variables of the child process. If NULL, the parent's environment is inherited. On Windows, many programs cannot function correctly if some environment variables are not set, so we always set HOMEDRIVE, HOMEPATH, LOGONSERVER, PATH, SYSTEMDRIVE, SYSTEMROOT, TEMP, USERDOMAIN, USERNAME, USERPROFILE and WINDIR. To append new environment variables to the ones set in the current process, specify "current" in env, without a name, and the appended ones with names. The appended ones can overwrite the current ones.
windows_verbatim_args: Whether to omit the escaping of the command and the arguments on windows. Ignored on other platforms.
windows_hide_window: Whether to hide the window of the application on windows. Ignored on other platforms.
encoding: The encoding to assume for stdout and stderr. By default the encoding of the current locale is used. Note that processx always reencodes the output of both streams in UTF-8 currently.
cleanup_tree: Whether to clean up the child process tree after the process has finished.
...: Extra arguments are passed to process$new(), see process. Note that you cannot pass stout or stderr here, because they are used internally by run(). You can use the stdout_callback, stderr_callback, etc. arguments to manage the standard output and error, or the process class directly if you need more flexibility.

Callbacks

Some notes about the callback functions. The first argument of a callback function is a character scalar (length 1 character), a single output or error line. The second argument is always the process object. You can manipulate this object, for example you can call $kill() on it to terminate it, as a response to a message on the standard output or error.

Error conditions

run() throws error condition objects if the process is interrupted, timeouts or fails (if error_on_status is TRUE):

On interrupt, a condition with classes system_command_interrupt, interrupt, condition is signalled. This can be caught with tryCatch(..., interrupt = ...).
On timeout, a condition with classes system_command_timeout_error, system_command_error, error, condition is thrown.
On error (if error_on_status is TRUE), an error with classes system_command_status_error, system_command_error, error, condition is thrown.

All of these conditions have the fields:

message: the error message,
stderr: the standard error of the process, or the standard output of the process if stderr_to_stdout was TRUE.
call: the captured call to run().
echo: the value of the echo argument.
stderr_to_stdout: the value of the stderr_to_stdout argument.
status: the exit status for system_command_status_error errors.

Details

run supports

Specifying a timeout for the command. If the specified time has passed, and the process is still running, it will be killed (with all its child processes).
Calling a callback function for each line or each chunk of the standard output and/or error. A chunk may contain multiple lines, and can be as short as a single character.
Cleaning up the subprocess, or the whole process tree, before exiting.

Examples

Run this code

# This works on Unix systems
run("ls")
system.time(run("sleep", "10", timeout = 1, error_on_status = FALSE))
system.time(
  run(
    "sh", c("-c", "for i in 1 2 3 4 5; do echo $i; sleep 1; done"),
    timeout = 2, error_on_status = FALSE
  )
)
if (FALSE) {
# This works on Windows systems, if the ping command is available
run("ping", c("-n", "1", "127.0.0.1"))
run("ping", c("-n", "6", "127.0.0.1"), timeout = 1,
    error_on_status = FALSE)
}

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