% File src/library/base/man/on.exit.Rd
% Part of the R package, http://www.R-project.org
% Copyright 1995-2007 R Core Development Team
% Distributed under GPL 2 or later

\name{on.exit}
\alias{on.exit}
\title{Function Exit Code}
\description{
  \code{on.exit} records the expression given as its argument as needing
  to be executed when the current function exits (either naturally or as
  the result of an error).  This is useful for resetting graphical
  parameters or performing other cleanup actions.

  If no expression is provided, i.e., the call is \code{on.exit()}, then
  the current \code{on.exit} code is removed.

  \code{on.exit} is a primitive function so positional matching is
  used and names of supplied arguments are ignored.
}
\usage{
on.exit(expr, add = FALSE)
}
\arguments{
  \item{expr}{an expression to be executed.}
  \item{add}{if TRUE, add \code{expr} to be executed after any previously
    set expressions; otherwise (the default) \code{expr} will overwrite
    any previously set expressions.}
}
\value{
  Invisible \code{NULL}.
}
\references{
  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
  \emph{The New S Language}.
  Wadsworth \& Brooks/Cole.
}
\seealso{
  \code{\link{sys.on.exit}} which returns the expression stored for use
  by \code{on.exit()} in the function in which \code{sys.on.exit()} is
  evaluated.  
}
\examples{
require(graphics)

opar <- par(mai = c(1,1,1,1))
on.exit(par(opar))
\dontshow{par(opar)}
}
\keyword{programming}