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libcurl-env(3)             Library Functions Manual             libcurl-env(3)


NAME

       libcurl-env - environment variables libcurl understands


DESCRIPTION

       libcurl reads and understands a set of environment variables that if
       set controls and changes behaviors. This is the full list of variables
       to set and description of what they do. Also note that curl, the
       command line tool, supports a set of additional environment variables
       independently of this.

       [scheme]_proxy
              When libcurl is given a URL to use in a transfer, it first
              extracts the scheme part from the URL and checks if there is a
              given proxy set for that in its corresponding environment
              variable. A URL like https://example.com makes libcurl use the
              http_proxy variable, while a URL like ftp://example.com uses the
              ftp_proxy variable.

              These proxy variables are also checked for in their uppercase
              versions, except the http_proxy one which is only used
              lowercase. Note also that some systems actually have a case
              insensitive handling of environment variables and then of course
              HTTP_PROXY still works.

              An exception exists for the WebSocket ws and wss URL schemes,
              where libcurl first checks ws_proxy or wss_proxy but if they are
              not set, it falls back and tries the http and https versions
              instead if set.

       ALL_PROXY
              This is a setting to set proxy for all URLs, independently of
              what scheme is being used. Note that the scheme specific
              variables overrides this one if set.

       CURL_SSL_BACKEND
              When libcurl is built to support multiple SSL backends, it
              selects a specific backend at first use. If no selection is done
              by the program using libcurl, this variable's selection is used.
              Setting a name that is not a built-in alternative makes libcurl
              stay with the default.

              SSL backend names (case-insensitive): BearSSL, GnuTLS, mbedTLS,
              nss, OpenSSL, rustls, Schannel, Secure-Transport, wolfSSL

       HOME   When the netrc feature is used (CURLOPT_NETRC(3)), this variable
              is checked as the primary way to find the "current" home
              directory in which the .netrc file is likely to exist.

       USERPROFILE
              When the netrc feature is used (CURLOPT_NETRC(3)), this variable
              is checked as the secondary way to find the "current" home
              directory (on Windows only) in which the .netrc file is likely
              to exist.

       LOGNAME
              Username to use when invoking the ntlm-wb tool, if NTLMUSER was
              not set.

       NO_PROXY
              This has the same functionality as the CURLOPT_NOPROXY(3)
              option: it gives libcurl a comma-separated list of hostname
              patterns for which libcurl should not use a proxy.

       NTLMUSER
              Username to use when invoking the ntlm-wb tool.

       SSLKEYLOGFILE
              When set and libcurl runs with a SSL backend that supports this
              feature, libcurl saves SSL secrets into the given filename.
              Using those SSL secrets, other tools (such as Wireshark) can
              decrypt the SSL communication and analyze/view the traffic.

              These secrets and this file might be sensitive. Users are
              advised to take precautions so that they are not stolen or
              otherwise inadvertently revealed.

       USER   Username to use when invoking the ntlm-wb tool, if NTLMUSER and
              LOGNAME were not set.


Debug Variables

       Debug variables are intended for internal use and are documented in
       libcurl-env-dbg(3).


SEE ALSO

       libcurl-env-dbg(3)

libcurl                          March 28 2024                  libcurl-env(3)

curl 8.7.1 - Generated Fri Mar 29 07:32:32 CDT 2024
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