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% File src/library/base/man/Sys.which.Rd
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% Part of the R package, https://www.R-project.org
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% Copyright 2007-2017 R Core Team
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% Distributed under GPL 2 or later
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\name{Sys.which}
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\alias{Sys.which}
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\title{Find Full Paths to Executables}
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\description{
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  This is an interface to the system command \code{which}, or to an
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  emulation on Windows.
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}
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\usage{
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Sys.which(names)
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}
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\arguments{
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  \item{names}{Character vector of names or paths of possible executables.}
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}
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\details{
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  The system command \command{which} reports on the full path names of
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  an executable (including an executable script) as would be executed by
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  a shell, accepting either absolute paths or looking on the path.
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  On Windows an \sQuote{executable} is a file with extension
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  \file{.exe}, \file{.com}, \file{.cmd} or \file{.bat}.  Such files need
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  not actually be executable, but they are what \code{\link{system}}
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  tries.
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  On a Unix-alike the full path to \code{which} (usually
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  \file{/usr/bin/which}) is found when \R is installed.
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}
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\value{
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  A character vector of the same length as \code{names}, named by
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  \code{names}.  The elements are either the full path to the
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  executable  or some indication that no executable of that name was
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  found.  Typically the indication is \code{""}, but this does depend on
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  the OS (and the known exceptions are changed to \code{""}).  Missing
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  values in \code{names} have missing return values.
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  On Windows the paths will be short paths (8+3 components, no spaces)
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  with \samp{\\} as the path delimiter.
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}
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\note{
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  Except on Windows this calls the system command \command{which}: since
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  that is not part of e.g.\sspace{}the POSIX standards, exactly what it does is
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  OS-dependent.  It will usually do tilde-expansion and it may make use
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  of \command{csh} aliases.
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}
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\examples{
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## the first two are likely to exist everywhere
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## texi2dvi exists on most Unix-alikes but not under MiKTeX
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Sys.which(c("ftp", "ping", "texi2dvi", "this-does-not-exist"))
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}
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\keyword{ utilities }