This is an interface to the system command which, or to an
emulation on Windows.
Character vector of names or paths of possible executables.
A character vector of the same length as names, named by
names. The elements are either the full path to the
executable or some indication that no executable of that name was
found. Typically the indication is "", but this does depend on
the OS (and the known exceptions are changed to ""). Missing
values in names have missing return values.
On Windows the paths will be short paths (8+3 components, no spaces)
with \ as the path delimiter.
The system command which reports on the full path names of
an executable (including an executable script) as would be executed by
a shell, accepting either absolute paths or looking on the path.
On Windows an ‘executable’ is a file with extension
.exe, .com, .cmd or .bat. Such files need
not actually be executable, but they are what system
On a Unix-alike the full path to which (usually
/usr/bin/which) is found when R is installed.