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  will  fall
                     back and try 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
                     User name 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  host  name  patterns  for  which  libcurl
                     should not use a proxy.

              NTLMUSER
                     User name 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 file name. 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   User  name  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)