download.file             package:utils             R Documentation

Download File from the Internet

Description:

     This function can be used to download a file from the Internet.

Usage:

     download.file(url, destfile, method, quiet = FALSE, mode = "w",
                   cacheOK = TRUE)

Arguments:

     url: A character string naming the URL of a resource to be
          downloaded.

destfile: A character string with the name where the downloaded file is
          saved.  Tilde-expansion is performed.

  method: Method to be used for downloading files.  Currently download
          methods '"internal"', '"wget"' and '"lynx"' are available,
          and there is a value '"auto"': see 'Details'.  The method can
          also be set through the option '"download.file.method"': see
          'options()'.

   quiet: If 'TRUE', suppress status messages (if any).

    mode: character.  The mode with which to write the file. Useful
          values are '"w"', '"wb"' (binary), '"a"' (append) and '"ab"'.
           Only used for the '"internal"' method.

 cacheOK: logical.  Is a server-side cached value acceptable?
          Implemented for the '"internal"' and '"wget"' methods.

Details:

     The function 'download.file' can be used to download a single file
     as described by 'url' from the internet and store it in
     'destfile'. The 'url' must start with a scheme such as
     '"http://"', '"ftp://"' or '"file://"'.

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

     'cacheOK = FALSE' is useful for '"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
     'available.packages'.

     The remaining details apply to method '"internal"' only.

     Note that 'https://' connections are not supported.

     See 'url' for how '"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 'timeout' which defaults to 60 seconds.

     The level of detail provided during transfer can be set by the
     'quiet' argument and the 'internet.info' option.  The details
     depend on the platform and scheme, but setting '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 '"wget"' can be used with proxy firewalls which require
     user/password authentication if proper values are stored in the
     configuration file for 'wget'.

Value:

     An (invisible) integer code, '0' for success and non-zero for
     failure.  For the '"wget"' and '"lynx"' methods this is the status
     code returned by the external program.  The '"internal"' method
     can return '1', but will in most cases throw an error.

Setting Proxies:

     This applies to the internal code only.

     Proxies can be specified via environment variables. Setting
     '"no_proxy"' to '"*"' stops any proxy being tried. Otherwise the
     setting of '"http_proxy"' or '"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 '"ftp_proxy_user"' and
     '"ftp_proxy_password"'.  The form of '"http_proxy"' should be
     '"http://proxy.dom.com/"' or '"http://proxy.dom.com:8080/"' where
     the port defaults to '80' and the trailing slash may be omitted.
     For '"ftp_proxy"' use the form '"ftp://proxy.dom.com:3128/"' where
     the default port is '21'.  These environment variables must be set
     before the download code is first used: they cannot be altered
     later by calling 'Sys.setenv'.

     Usernames and passwords can be set for HTTP proxy transfers via
     environment variable 'http_proxy_user' in the form 'user:passwd'. 
     Alternatively, 'http_proxy' can be of the form
     '"http://user:pass@proxy.dom.com:8080/"' for compatibility with
     'wget'.  Only the HTTP/1.0 basic authentication scheme is
     supported.

Note:

     Methods '"wget"' and '"lynx"' are for historical compatibility. 
     They will block all other activity on the R process.

     For methods '"wget"' and '"lynx"' a system call is made to the
     tool given by 'method', and the respective program must be
     installed on your system and be in the search path for
     executables.

See Also:

     'options' to set the 'HTTPUserAgent', 'timeout' and
     'internet.info' options.

     'url' for a finer-grained way to read data from URLs.

     'url.show', 'available.packages', 'download.packages' for
     applications

