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.
`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 chosen for file:// URLs, and for the others provided `capabilities("http/ftp")` is true (which it almost always is). Otherwise methods `"wget"`, `"curl"` 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:// URLs 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 sign represents 2% of the transfer completed: otherwise a dot represents 10Kb.

Code written to download binary files must use `mode = "wb"`, but the problems incurred by a text transfer will only be seen on Windows.

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 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.

### 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.

Contributed package RCurl provides more comprehensive facilities to download from URLs.

[Package utils version 2.15.1 Index]