CURLOPT_PROXY.3: describe the environment variables more

tunnel through the HTTP proxy. Such tunneling is activated with

\fICURLOPT_HTTPPROXYTUNNEL(3)\fP.

libcurl respects the environment variables \fBhttp_proxy\fP, \fBftp_proxy\fP,

\fBall_proxy\fP etc, if any of those are set. The \fICURLOPT_PROXY(3)\fP

option does however override any possibly set environment variables.

Setting the proxy string to "" (an empty string) will explicitly disable the

use of a proxy, even if there is an environment variable set for it.

The application does not have to keep the string around after setting this

option.

.SH "Environment variables"

libcurl respects the proxy environment variables named \fBhttp_proxy\fP,

\fBftp_proxy\fP, \fBsftp_proxy\fP etc. If set, libcurl will use the specified

proxy for that URL scheme. So for a "FTP://" URL, the \fBftp_proxy\fP is

considered. \fBall_proxy\fP is used if no protocol specific proxy was set.

If \fBno_proxy\fP (or \fBNO_PROXY\fP) is set, it can specify a list of host

names to not use a proxy for (even if one of the previous mention variables

are set). That is the exact equivalent of setting the \fBCURLOPT_NOPROXY(3)\fP

option.

The \fICURLOPT_PROXY(3)\fP option overrides environment variables.

.SH DEFAULT

Default is NULL, meaning no proxy is used.