proxy protocol docs: rephrased and updated

This option overrides any previous use of \fI-x, --proxy\fP, as they are

mutually exclusive.

Since 7.21.7, this option is superfluous since you can specify a

socks5-hostnamae proxy with \fI-x, --proxy\fP using a socks5h:// protocol

prefix.

Since 7.21.7, this option is superfluous since you can specify a socks5

hostname proxy with \fI-x, --proxy\fP using a socks5h:// protocol prefix.

If this option is used several times, the last one will be used. (This option

was previously wrongly documented and used as --socks without the number

The environment variables can be specified in lower case or upper case. The

lower case version has precedence. http_proxy is an exception as it is only

available in lower case.

Using an environment variable to set the proxy has the same effect as using

the \fI--proxy\fP option.

.IP "http_proxy [protocol://]<host>[:port]"

Sets the proxy server to use for HTTP.

.IP "HTTPS_PROXY [protocol://]<host>[:port]"

Sets the proxy server to use for HTTPS.

.IP "FTP_PROXY [protocol://]<host>[:port]"

Sets the proxy server to use for FTP.

.IP "[url-protocol]_PROXY [protocol://]<host>[:port]"

Sets the proxy server to use for [url-protocol], where the protocol is a

protocol that curl supports and as specified in a URL. FTP, FTPS, POP3, IMAP,

SMTP, LDAP etc.

.IP "ALL_PROXY [protocol://]<host>[:port]"

Sets the proxy server to use if no protocol-specific proxy is set.

.IP "NO_PROXY <comma-separated list of hosts>"

list of host names that shouldn't go through any proxy. If set to a asterisk

\&'*' only, it matches all hosts.

Since 7.21.7, the proxy string may be specified with a protocol:// prefix to

specify alternative proxy protocols. Use socks4://, socks4a:// or socks5:// to

request the specific SOCKS version to be used. No protocol specified, http://

and all others will be treated as HTTP proxies.

.SH "PROXY PROTOCOL PREFIXES"

Since curl version 7.21.7, the proxy string may be specified with a

protocol:// prefix to specify alternative proxy protocols.

If no protocol is specified in the proxy string or if the string doesn't match

a supported one, the proxy will be treated as a HTTP proxy.

The supported proxy protocol prefixes are as follows:

.IP "socks4://"

Makes it the equivalent of \fI--socks4\fP

.IP "socks4a://"

Makes it the equivalent of \fI--socks4a\fP

.IP "socks5://"

Makes it the equivalent of \fI--socks5\fP

.IP "socks5h://"

Makes it the equivalent of \fI--socks5-hostname\fP

.SH EXIT CODES

There are a bunch of different error codes and their corresponding error

messages that may appear during bad conditions. At the time of this writing,

.SH "SEE ALSO"

.BR ftp (1),

.BR wget (1)