R: Download File from the Internet

download.file {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, extra = getOption("download.file.extra"))

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"`, `"curl"` 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), and the progress bar.
`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. (See also ‘Details’.)
`cacheOK`	logical. Is a server-side cached value acceptable? Implemented for the `"internal"`, `"wget"` and `"curl"` methods.
`extra`	character vector of additional command-line arguments for the `"wget"`, `"curl"` and `"lynx"` 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 used on Windows.

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:// URLs are only supported if --internet2 or environment variable R_WIN_INTERNET2 was set or setInternet2(TRUE) was used (to make use of Internet Explorer internals), and then only if the certificate is considered to be valid.

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, the full width of the bar is the known length. Otherwise the initial width represents 100 Kbytes and is doubled whenever the current width is exceeded.

If mode is not supplied and url ends in one of .gz, .bz2, .xz, .tgz, .zip, .rda or .RData a binary transfer is done. Since Windows (unlike Unix-alikes) does distinguish between text and binary files, care is needed that other binary file types are transferred with mode = "wb".

There is an alternative method if you have Internet Explorer 4 or later installed. You can use the command line flag --internet2, or call setInternet2(TRUE) and then the ‘Internet Options’ of the system are used to choose proxies and so on; these are set in the Control Panel and are those used for Internet Explorer. That version does not support cacheOK = FALSE.

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. Under Windows, if http_proxy_user is set to "ask" then a dialog box will come up for the user to enter the username and password. NB: you will be given only one opportunity to enter this, but if proxy authentication is required and fails there will be one further prompt per download.

Note

Methods "wget" and "lynx" are mainly for historical compatibility, but they and "curl" can be used for URLs (e.g. https:// URLs or those than use cookies) which the internal method does not support. They will block all other activity on the R process.

For methods "wget", "curl"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.