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% File src/library/base/man/Sys.setenv.Rd
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% Part of the R package, http://www.R-project.org
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% Copyright 1995-2011 R Core Team
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% Distributed under GPL 2 or later
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\name{Sys.setenv}
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\alias{Sys.setenv}
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\alias{Sys.unsetenv}
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\title{Set or Unset Environment Variables}
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\usage{
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Sys.setenv(\dots)
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Sys.unsetenv(x)
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}
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\arguments{
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  \item{\dots}{named arguments with values coercible to a character string.}
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  \item{x}{a character vector, or an object coercible to character.}
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}
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\description{
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  \code{Sys.setenv} sets environment variables (for other processes
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  called from within \R or future calls to \code{\link{Sys.getenv}} from
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  this \R process).
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  \code{Sys.unsetenv} removes environment variables.
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}
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\value{
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  A logical vector, with elements being true if (un)setting the
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  corresponding variable succeeded.  (For \code{Sys.unsetenv} this
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  includes attempting to remove a non-existent variable.)
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}
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\details{
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  Non-standard \R names must be quoted in \code{Sys.setenv}: see the
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  examples.  Most platforms (and POSIX) do not allow names containing
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  \code{"="}.  Windows does, but the facilities provided by \R may not
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  handle these correctly so they should be avoided.  Most platforms
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  allow setting an environment variable to \code{""}, but Windows does
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  not, and there \code{Sys.setenv(FOO = "")} unsets \env{FOO}.
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  There may be system-specific limits on the maximum length of the values
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  of individual environment variables or of all environment variables.
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#ifdef windows
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  Windows has a limit of 32,767 characters on the environment block, and
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  \code{cmd.exe} has a limit of 2047 (Windows 2000) or 8192 characters
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  (XP and later) for each value.
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#endif
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}
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% http://support.microsoft.com/kb/830473
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#ifdef unix
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\note{
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  If \code{Sys.unsetenv} is not supported, it will at least try to
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  set the value of the environment variable to \code{""}, with a
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  warning.
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}
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#endif
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\seealso{
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  \code{\link{Sys.getenv}}, \link{Startup} for ways to set environment
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  variables for the \R session.
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  \code{\link{setwd}} for the working directory.
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  The help for \sQuote{\link{environment variables}} lists many of the
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  environment variables used by \R.
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}
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\examples{
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print(Sys.setenv(R_TEST = "testit", "A+C" = 123))  # `A+C` could also be used
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Sys.getenv("R_TEST")
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#ifdef windows
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Sys.unsetenv("R_TEST")
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#endif
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#ifdef unix
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Sys.unsetenv("R_TEST")  # may warn and not succeed
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#endif
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Sys.getenv("R_TEST", unset = NA)
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}
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\keyword{environment}
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\keyword{utilities}