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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 or :8080/ where the port defaults to 80 and the trailing slash may be omitted. For ftp_proxy use the form :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.
Download 92A0685B8C7A4884E8704AD070C6D88456970F59 rar
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.
This is an issue for method = "libcurl" on Windows, where the OS does not provide a suitable CA certificate bundle, so by default on Windows certificates are not verified. To turn verification on, set environment variable CURL_CA_BUNDLE to the path to a certificate bundle file, usually named ca-bundle.crt or curl-ca-bundle.crt. (This is normally done for a binary installation of R, which installs R_HOME/etc/curl-ca-bundle.crt and sets CURL_CA_BUNDLE to point to it if that environment variable is not already set.) For an updated certificate bundle, see Currently one can download a copy from -bundle/master/ca-bundle.crt and set CURL_CA_BUNDLE to the full path to the downloaded file.
If you use download.file in a package or script, you must check the return value, since it is possible that the download will fail with a non-zero status but not an R error. (This was more likely prior to R 3.4.0.)
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://, https://, ftp:// or file://.
When method "libcurl" is used, it provides (non-blocking) access to https:// and (usually) ftps:// URLs. There is support for simultaneous downloads, so url and destfile can be character vectors of the same length greater than one (but the method has to be specified explicitly and not via "auto"). For a single URL and quiet = FALSE a progress bar is shown in interactive use. 041b061a72