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,  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                                            2025-03-05                                     libcurl-env(3)