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+<!-- Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. -->
+<!-- SPDX-License-Identifier: curl -->
+# ENVIRONMENT
+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 --proxy option.
+
+## `http_proxy` [protocol://]<host>[:port]
+Sets the proxy server to use for HTTP.
+
+## `HTTPS_PROXY` [protocol://]<host>[:port]
+Sets the proxy server to use for HTTPS.
+
+## `[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.
+
+## `ALL_PROXY` [protocol://]<host>[:port]
+Sets the proxy server to use if no protocol-specific proxy is set.
+
+## `NO_PROXY` <comma-separated list of hosts/domains>
+list of host names that should not go through any proxy. If set to an asterisk
+'*' only, it matches all hosts. Each name in this list is matched as either
+a domain name which contains the hostname, or the hostname itself.
+
+This environment variable disables use of the proxy even when specified with
+the --proxy option. That is
+
+    NO_PROXY=direct.example.com curl -x http://proxy.example.com
+    http://direct.example.com
+
+accesses the target URL directly, and
+
+    NO_PROXY=direct.example.com curl -x http://proxy.example.com
+    http://somewhere.example.com
+
+accesses the target URL through the proxy.
+
+The list of host names can also be include numerical IP addresses, and IPv6
+versions should then be given without enclosing brackets.
+
+IP addresses can be specified using CIDR notation: an appended slash and
+number specifies the number of "network bits" out of the address to use in the
+comparison (added in 7.86.0). For example "192.168.0.0/16" would match all
+addresses starting with "192.168".
+
+## `APPDATA` <dir>
+On Windows, this variable is used when trying to find the home directory. If
+the primary home variable are all unset.
+
+## `COLUMNS` <terminal width>
+If set, the specified number of characters is used as the terminal width when
+the alternative progress-bar is shown. If not set, curl tries to figure it out
+using other ways.
+
+## `CURL_CA_BUNDLE` <file>
+If set, it is used as the --cacert value. This environment variable is ignored
+if Schannel is used as the TLS backend.
+
+## `CURL_HOME` <dir>
+If set, is the first variable curl checks when trying to find its home
+directory. If not set, it continues to check *XDG_CONFIG_HOME*
+
+## `CURL_SSL_BACKEND` <TLS backend>
+If curl was built with support for "MultiSSL", meaning that it has built-in
+support for more than one TLS backend, this environment variable can be set to
+the case insensitive name of the particular backend to use when curl is
+invoked. Setting a name that is not a built-in alternative makes curl stay
+with the default.
+
+SSL backend names (case-insensitive): **bearssl**, **gnutls**, **mbedtls**,
+**openssl**, **rustls**, **schannel**, **secure-transport**, **wolfssl**
+
+## `HOME` <dir>
+If set, this is used to find the home directory when that is needed. Like when
+looking for the default .curlrc. *CURL_HOME* and *XDG_CONFIG_HOME*
+have preference.
+
+## `QLOGDIR` <directory name>
+If curl was built with HTTP/3 support, setting this environment variable to a
+local directory makes curl produce **qlogs** in that directory, using file
+names named after the destination connection id (in hex). Do note that these
+files can become rather large. Works with the ngtcp2 and quiche QUIC backends.
+
+## `SHELL`
+Used on VMS when trying to detect if using a **DCL** or a **unix** shell.
+
+## `SSL_CERT_DIR` <dir>
+If set, it is used as the --capath value. This environment variable is ignored
+if Schannel is used as the TLS backend.
+
+## `SSL_CERT_FILE` <path>
+If set, it is used as the --cacert value. This environment variable is ignored
+if Schannel is used as the TLS backend.
+
+## `SSLKEYLOGFILE` <file name>
+If you set this environment variable to a file name, curl stores TLS secrets
+from its connections in that file when invoked to enable you to analyze the
+TLS traffic in real time using network analyzing tools such as Wireshark. This
+works with the following TLS backends: OpenSSL, libressl, BoringSSL, GnuTLS
+and wolfSSL.
+
+## `USERPROFILE` <dir>
+On Windows, this variable is used when trying to find the home directory. If
+the other, primary, variable are all unset. If set, curl uses the path
+**"$USERPROFILE\Application Data"**.
+
+## `XDG_CONFIG_HOME` <dir>
+If *CURL_HOME* is not set, this variable is checked when looking for a
+default .curlrc file.