\HeaderA{download.file}{Download File from the Internet}{download.file}
\keyword{utilities}{download.file}
\begin{Description}\relax
This function can be used to download a file from the Internet.
\end{Description}
\begin{Usage}
\begin{verbatim}
download.file(url, destfile, method, quiet = FALSE, mode = "w",
              cacheOK = TRUE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{url}] A character string naming the URL of a resource to be
downloaded.
\item[\code{destfile}] A character string with the name where the downloaded
file is saved.  Tilde-expansion is performed.
\item[\code{method}] Method to be used for downloading files.  Currently
download methods \code{"internal"}, \code{"wget"} and \code{"lynx"}
are available, and there is a value \code{"auto"}: see Details.  The
method can also be set through the option
\code{"download.file.method"}: see \code{\LinkA{options}{options}()}.
\item[\code{quiet}] If \code{TRUE}, suppress status messages (if any).
\item[\code{mode}] character.  The mode with which to write the file. Useful
values are \code{"w"}, \code{"wb"} (binary), \code{"a"} (append) and
\code{"ab"}.  Only used for the \code{"internal"} method.
\item[\code{cacheOK}] logical.  Is a server-side cached value acceptable?
Implemented for the \code{"internal"} and \code{"wget"} methods.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The function \code{download.file} can be used to download a single
file as described by \code{url} from the internet and store it in
\code{destfile}.
The \code{url} must start with a scheme such as
\code{"http://"}, \code{"ftp://"} or \code{"file://"}.

If \code{method = "auto"} is chosen (the default), the internal method
is chosen for \code{"file://"} URLs, and for the others provided
\code{\LinkA{capabilities}{capabilities}("http/ftp")} is true (which it almost always
is).  Otherwise methods \code{"wget"} and \code{"lynx"} are tried in turn.

\code{cacheOK = FALSE} is useful for \code{"http://"} URLs, and will
attempt to get a copy directly from the site rather than from an
intermediate cache.  (Not all platforms support it.)
It is used by \code{\LinkA{available.packages}{available.packages}}.

The remaining details apply to method \code{"internal"} only.

See \code{\LinkA{url}{url}} for how \code{"file://"} URLs are interpreted,
especially on Windows.  This function does decode encoded URLs.

The timeout for many parts of the transfer can be set by the option
\code{timeout} which defaults to 60 seconds.

The level of detail provided during transfer can be set by the
\code{quiet} argument and the \code{internet.info} option.  The
details depend on the platform and scheme, but setting
\code{internet.info} to 0 gives all available details, including
all server responses. Using 2 (the default) gives only serious
messages, and 3 or more suppresses all messages.

A progress bar tracks the transfer. If the file length is known, an
equals represents 2\% of the transfer completed: otherwise a dot
represents 10Kb.

Method \code{"wget"} can be used with proxy firewalls which require
user/password authentication if proper values are stored in the
configuration file for \code{wget}.
\end{Details}
\begin{Value}
An (invisible) integer code, \code{0} for success and non-zero for
failure.  For the \code{"wget"} and \code{"lynx"} methods this is the
status code returned by the external program.  The \code{"internal"}
method can return \code{1}, but will in most cases throw an error.
\end{Value}
\begin{Section}{Setting Proxies}
This applies to the internal code only.

Proxies can be specified via environment variables.
Setting \code{"no\_proxy"} stops any proxy being tried.
Otherwise the setting of \code{"http\_proxy"} or \code{"ftp\_proxy"}
(or failing that, the all upper-case version) is consulted and if
non-empty used as a proxy site.  For FTP transfers, the username
and password on the proxy can be specified by \code{"ftp\_proxy\_user"}
and \code{"ftp\_proxy\_password"}.  The form of \code{"http\_proxy"}
should be \code{"http://proxy.dom.com/"} or
\code{"http://proxy.dom.com:8080/"} where the port defaults to
\code{80} and the trailing slash may be omitted. For
\code{"ftp\_proxy"} use the form \code{"ftp://proxy.dom.com:3128/"}
where the default port is \code{21}.  These environment variables
must be set before the download code is first used: they cannot be
altered later by calling \code{Sys.putenv}.

Usernames and passwords can be set for HTTP proxy transfers via
environment variable \env{http\_proxy\_user} in the form
\code{user:passwd}.  Alternatively, \code{"http\_proxy"} can be of the
form \code{"http://user:pass@proxy.dom.com:8080/"} for compatibility
with \code{wget}.  Only the HTTP/1.0 basic authentication scheme is
supported.
\end{Section}
\begin{Note}\relax
Methods \code{"wget"} and \code{"lynx"} are for historical
compatibility.  They will block all other activity on the \R{} process.

For methods \code{"wget"} and \code{"lynx"} a system call is made to
the tool given by \code{method}, and the respective program must be
installed on your system and be in the search path for executables.
\end{Note}
\begin{SeeAlso}\relax
\code{\LinkA{options}{options}} to set the \code{timeout} and
\code{internet.info} options.

\code{\LinkA{url}{url}} for a finer-grained way to read data from URLs.

\code{\LinkA{url.show}{url.show}}, \code{\LinkA{available.packages}{available.packages}},
\code{\LinkA{download.packages}{download.packages}} for applications
\end{SeeAlso}

