libcurl-env(3)           libcurl environment variables          libcurl-env(3)

NAME
       libcurl-env - environment variables libcurl understands

DESCRIPTION
       libcurl reads and understands a set of environment variables that if
       set will control and change 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" will hence use the
              "http_proxy" variable, while a URL like "ftp://example.com" will
              use 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" will still work...

       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 will override this one if set.

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

              SSL backend names (case-insensitive): bearssl, gnutls, gskit,
              mbedtls, mesalink, 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.

       LOGNAME
              User name to use when invoking the ntlm-wb tool, if NTLMUSER
              wasn't set.

       NO_PROXY
              This has the same functionality as the _NOPROXY&section=3">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 will save 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.

       SSL_DIR
              When libcurl runs with the NSS backends for TLS features, this
              variable is used to find the directory for NSS PKI database
              instead of the built-in.

       USER   User name to use when invoking the ntlm-wb tool, if NTLMUSER and
              LOGNAME weren't set.

Debug Variables
       There's a set of variables only recognized and used if libcurl was
       built "debug enabled", which should never be true for a library used in
       production.

       CURL_GETHOSTNAME
              Debug-only variable.

       CURL_FORCETIME
              Debug-only variable.

       CURL_ENTROPY
              Debug-only variable. Used to set a fixed faked value to use
              instead of a proper random number so that functions in libcurl
              that are otherwise getting random outputs can be tested for what
              they generate.

       CURL_TRACE
              Debug-only variable. Used for debugging the lib/ldap
              implementation.

       CURL_NTLM_WB_FILE
              Debug-only variable. Used to set to a debug-version of the ntlm-
              wb executable.

       CURL_OPENLDAP_TRACE
              Debug-only variable. Used for debugging the lib/openldap.c
              implementation.

libcurl 7.77.0                  March 27, 2021                  libcurl-env(3)