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% File src/library/utils/man/savehistory.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2013 R Core Team
% Distributed under GPL 2 or later

\name{savehistory}
\alias{loadhistory}
\alias{savehistory}
\alias{history}
\alias{timestamp}
\title{Load or Save or Display the Commands History}
\description{
  Load or save or display the commands history.
}
\usage{
loadhistory(file = ".Rhistory")
savehistory(file = ".Rhistory")

history(max.show = 25, reverse = FALSE, pattern, \dots)

timestamp(stamp = date(),
          prefix = "##------ ", suffix = " ------##",
          quiet = FALSE)
}
\arguments{
  \item{file}{The name of the file in which to save the history, or
    from which to load it. The path is relative to the current
    working directory.}
  \item{max.show}{The maximum number of lines to show. \code{Inf} will
    give all of the currently available history.}
  \item{reverse}{logical. If true, the lines are shown in reverse
    order. Note: this is not useful when there are continuation lines.}
  \item{pattern}{A character string to be matched against the lines of
    the history.  When supplied, only \emph{unique} matching lines are shown.}
  \item{\dots}{Arguments to be passed to \code{\link{grep}} when doing
    the matching.}
  \item{stamp}{A value or vector of values to be written into the history.}
  \item{prefix}{A prefix to apply to each line.}
  \item{suffix}{A suffix to apply to each line.}
  \item{quiet}{If \code{TRUE}, suppress printing timestamp to the console.}
}
\details{
  There are several history mechanisms available for the different \R
  consoles, which work in similar but not identical ways.  There are
  separate versions of this help file for Unix and Windows.

#ifdef windows
  The functions described here work in \command{Rgui} and interactive
  \command{Rterm} but not in batch use of \command{Rterm} nor in
  embedded/DCOM versions.

  The history mechanism is
#endif
#ifdef unix
  The functions described here work on Unix-alikes under the
  \code{readline} command-line interface but may not otherwise (for
  example, in batch use or in an embedded application).  Note that \R
  can be built without \code{readline}.

  \command{R.app}, the console on macOS, has a separate and largely
  incompatible history mechanism, which by default uses a file
  \file{.Rapp.history} and saves up to 250 entries.  These functions are
  not currently implemented there.

  The \code{readline} history mechanism
#endif
  is controlled by two environment variables: \env{R_HISTSIZE} controls
  the number of lines that are saved (default 512), and \env{R_HISTFILE}
  (default \file{.Rhistory}) sets the filename used for the
  loading/saving of history if requested at the beginning/end of a
  session (but not the default for
  \code{loadhistory}/\code{savehistory}).  There is no limit on the
  number of lines of history retained during a session, so setting
  \env{R_HISTSIZE} to a large value has no penalty unless a large file
  is actually generated.

  These environment variables are read at the time of saving, so can be
  altered within a session by the use of \code{\link{Sys.setenv}}.

#ifdef unix
  Note that \code{readline} history library saves files with permission
  \code{0600}, that is with read/write permission for the user and not
  even read permission for any other account.
#endif

  The \code{timestamp} function writes a timestamp (or other message)
  into the history and echos it to the console.  On platforms that do not
  support a history mechanism only the console message is printed.
}
\note{
  If you want to save the history at the end of (almost) every
  interactive session (even those in which you do not save the
  workspace), you can put a call to \code{savehistory()} in
  \code{\link{.Last}}.  See the examples.
}
\examples{\dontrun{
## Save the history in the home directory: note that it is not
## (by default) read from there but from the current directory
.Last <- function()
    if(interactive()) try(savehistory("~/.Rhistory"))
}}
\keyword{utilities}