The R Project SVN R

\name{shell}
\alias{shell}
\title{Invoke a System Command, using a Shell}
\usage{
shell(cmd, shell, flag="/c", intern=FALSE, wait=TRUE,
      translate=FALSE, mustWork=FALSE)
}
\arguments{
    \item{cmd}{the system command to be invoked, as a string.}
    \item{shell}{a string giving the name of the shell to be used, or
    \code{NULL} (no shell). If missing, a suitable shell is chosen:
    see `details'}
    \item{flag}{the switch to run a command under the shell. If the
    shell is \code{bash} or \code{tcsh} the default is changed to
    \code{"-c"}.}
    \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{translate}{If \code{TRUE}, \code{"/"} in \code{cmd} is
    translated to \code{"\\"}.}
    \item{mustWork}{a logical; if \code{TRUE} failure to run the command
    will give an \R error.}
}
\description{
    \code{shell} runs the command specified by \code{cmd}, usually under
    a shell.
}
\value{
    If \code{intern=TRUE}, a character vector giving the output of the
    command, one line per character string, or an error message if the
    command could not be run.

    If \code{intern=FALSE}, the return value is a error code, given the
    invisible attribute (so needs to be printed explictly). 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=FALSE} the value
    is the error code returned by the command, and if \code{wait=TRUE}
    it is the zero (the conventional success value),

    If \code{intern=FALSE} and \code{wait=TRUE} (the defaults) 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{
    If no \code{shell} is specified, the environment variables
    \code{R\_SHELL}, \code{SHELL} and \code{COMSPEC} are tried in turn:
    \code{COMSPEC} should always succeed. Using \code{shell=NULL}
    invokes the command \code{cmd} directly, in which case an extension
    of \code{.exe} is assumed. It is possible to use batch files
    directly if their extension is given: Windows (rather than \R) then
    chooses a shell.
    
    See \code{\link{system}} for fuller details: \code{shell} is a more
    user-friendly wrapper for \code{system}.
}
\author{B. D. Ripley}

\seealso{\code{\link{system}}}

\keyword{utilities}