curl/docs/cmdline-opts/_ENVIRONMENT.md

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://][:port]

Sets the proxy server to use for HTTP.

HTTPS_PROXY [protocol://][:port]

Sets the proxy server to use for HTTPS.

[url-protocol]_PROXY [protocol://][: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://][:port]

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

NO_PROXY

list of hostnames 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 hostnames 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

On Windows, this variable is used when trying to find the home directory. If the primary home variable are all unset.

COLUMNS

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

If set, it is used as the --cacert value. This environment variable is ignored if Schannel is used as the TLS backend.

CURL_HOME

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

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

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

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

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

If set, it is used as the --cacert value. This environment variable is ignored if Schannel is used as the TLS backend.

SSLKEYLOGFILE

If you set this environment variable to a filename, 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 (TLS 1.2 max), BoringSSL, GnuTLS and wolfSSL.

USERPROFILE

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

If CURL_HOME is not set, this variable is checked when looking for a default .curlrc file.