\name{system}
\alias{system}
\alias{unix}
\title{Invoke a System Command}
\usage{
system(command, intern = FALSE, wait = TRUE, input = NULL,
       show.output.on.console = FALSE,
       minimized = FALSE, invisible = FALSE)
}
\arguments{
    \item{command}{the system command to be invoked, as a string.}
    \item{intern}{a logical, indicates whether to make the output of the
	command an \R object.}
    \item{wait}{should the \R interpreter wait for the command to finish?
	The default is to wait, and the interpreter will always wait if
	\code{intern = TRUE}.}
    \item{input}{if a character vector is supplied, this is copied one
	string per line to a temporary file, and the standard input of
	\code{command} is redirected to the file.}
    \item{show.output.on.console}{a logical, indicates whether to capture
          the output of the command and show it on the \R console (not used
	  by \code{Rterm}, which captures the output unless \code{wait}
	  is false).}
    \item{minimized}{a logical, indicates whether the command window
	  should be initially displayed as a minimized window.}
    \item{invisible}{a logical, indicates whether the command window
	  should be visible on the screen.}
}
\description{
    \code{system} invokes the system command specified by \code{command}.
}
\value{
  If \code{intern = TRUE}, a character vector giving the output of the
  command, one line per character string.  If the command could not be
  run or gives an error a \R error is generated.  (Output lines of more
  than 8095 characters will be split.)

  If \code{intern = FALSE}, the return value is an error code, given the
  invisible attribute (so needs to be printed explicitly). If the
  command could not be run for any reason, the value is \code{-1} and
  an \R warning is generated.  Otherwise if \code{wait = TRUE} the value
  is the error code returned by the command, and if \code{wait = FALSE}
  it is the zero (the conventional success value),

  If \code{intern = FALSE} and \code{show.output.on.console = TRUE}
  the text output from a command that is a console application will
  appear in the \R console (\code{Rgui}) or the window running \R
  (\code{Rterm}).
}
\details{
  \code{cmd} is parsed as a command plus arguments separated by spaces.
  So if the path to the command contains spaces, it must be
  (double-)quoted.  See the examples.  (Note: a Windows path name cannot
  contain a double quote, so we do not need to worry about escaping
  embedded quotes.)

  The command is run directly as a Windows command by the Windows API
  call \code{CreateProcess}: extensions of \code{.exe}, \code{.com},
  \code{.cmd} and \code{.bat} are tried in turn if none
  is supplied. (To use DOS internal commands use
  \code{paste(Sys.getenv("COMSPEC"),"/c",cmd)}.)
  The search path for \code{command}
  may be system-dependent: it will include the \R \code{bin}
  directory, the working directory and the Windows system directories
  before \code{PATH}.

  Precisely what is seen by the user depends on whether \code{Rgui} or
  \code{Rterm} is being used.  For \code{Rgui} a new console will
  always be used, so a commands window will appear for the duration of
  console applications unless \code{invisible} is true. For
  \code{Rterm} a separate commands window
  will appear for console applications only if \code{wait = FALSE}.

  \code{unix} is a \emph{deprecated} alternative, available for
  backwards compatibility.
}
\section{Warning}{
  The command cannot be interrupted by the \R process.

  Do not run console applications that require user
  input from \code{Rgui} setting \code{intern = TRUE} and/or
  \code{show.output.on.console = TRUE}. They will not work,
  may hang and then will probably hang \code{Rgui} too.
}

\seealso{
  \code{\link{shell}} or \code{\link{shell.exec}} for a less raw
  interface.
}

\examples{
# launch an editor, wait for it to quit
\dontrun{system("notepad myfile.txt")}
# launch a Windows 9x process monitor (from Win9x KernelToys)
\dontrun{system("wintop", wait = FALSE)}
# launch your favourite shell:
\dontrun{system(Sys.getenv("COMSPEC"))}
\dontrun{
## note the two sets of quotes here:
system(paste('"c:/Program Files/Mozilla Firefox/firefox.exe"',
             '-url cran.r-project.org'), wait = FALSE)}
}
\keyword{interface}
\keyword{file}
\keyword{utilities}