\HeaderA{libPaths}{Search Paths for Packages}{libPaths}
\aliasA{.expand\_R\_libs\_env\_var}{libPaths}{.expand.Rul.R.Rul.libs.Rul.env.Rul.var}
\aliasA{.libPaths}{libPaths}{.libPaths}
\aliasA{.Library}{libPaths}{.Library}
\methaliasA{.Library.site}{libPaths}{.Library.site}
\aliasA{R\_LIBS}{libPaths}{R.Rul.LIBS}
\aliasA{R\_LIBS\_SITE}{libPaths}{R.Rul.LIBS.Rul.SITE}
\aliasA{R\_LIBS\_USER}{libPaths}{R.Rul.LIBS.Rul.USER}
\keyword{data}{libPaths}
\begin{Description}\relax
\code{.libPaths} gets/sets the library trees within which packages are
looked for.
\end{Description}
\begin{Usage}
\begin{verbatim}
.libPaths(new)

.Library
.Library.site
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{new}] a character vector with the locations of \R{} library
trees.  Tilde expansion (\code{\LinkA{path.expand}{path.expand}}) is done, and if
any element contains one of \code{*?[}, globbing is done where
supported by the platform: see \code{\LinkA{Sys.glob}{Sys.glob}}.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
\code{.Library} is a character string giving the location of the
default library, the \file{library} subdirectory of \env{R\_HOME}.

\code{.Library.site} is a (possibly empty) character vector giving the
locations of the site libraries, by default the \file{site-library}
subdirectory of \env{R\_HOME} (which may not exist).

\code{.libPaths} is used for getting or setting the library trees that
\R{} knows about (and hence uses when looking for packages).  If called
with argument \code{new}, the library search path is set to
the existing directories in \code{unique(c(new, .Library.site, .Library))}
and this is returned.  If given no argument, a character vector with
the currently active library trees is returned.

The library search path is initialized at startup from the environment
variable \env{R\_LIBS} (which should be a colon-separated list of
directories at which \R{} library trees are rooted) followed by those in
environment variable \env{R\_LIBS\_USER}.  Only directories which exist
at the time will be included.

By default \env{R\_LIBS} is unset, and \env{R\_LIBS\_USER} is set to
directory \file{R/\var{R.version\$platform}-library/\var{x.y}}
of the home directory (or \file{Library/R/\var{x.y}/library} for
Mac OS X AQUA builds), for \R{} \var{x.y.z}.

\code{.Library.site} can be set via the environment variable 
\env{R\_LIBS\_SITE} (as a colon-separated list of library trees).

Both \env{R\_LIBS\_USER} and \env{R\_LIBS\_SITE} feature possible
expansion of specifiers for \R{} version specific information as part of
the startup process.  The possible conversion specifiers all start
with a \samp{\%} and are followed by a single letter (use \samp{\%\%}
to obtain \samp{\%}), with currently available conversion
specifications as follows:
\describe{
\item[\code{\%V}] \R{} version number including the patchlevel (e.g.,
\samp{2.5.0}).
\item[\code{\%v}] \R{} version number excluding the patchlevel (e.g.,
\samp{2.5}).
\item[\code{\%p}] the platform for which \R{} was built.
\item[\code{\%o}] the underlying operating system.
\item[\code{\%a}] the architecture (CPU) \R{} was built on/for.
}
(See \code{\LinkA{version}{version}} for details on R version information.)

Function \code{.libPaths} always uses the values of \code{.Library}
and \code{.Library.site} in the base name space.  \code{.Library.site}
can be set by the site in \file{Rprofile.site}, which should be
followed by a call to \code{.libPaths(.libPaths())} to make use of the
updated value.
\end{Details}
\begin{Value}
A character vector of file paths.
\end{Value}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{library}{library}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
.libPaths()                 # all library trees R knows about
\end{ExampleCode}
\end{Examples}

