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  is  not  a  built-in
              alternative will make libcurl stay with the default.

              SSL  backend  names  (case-insensitive):  BearSSL,  GnuTLS,  gskit,  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
              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  were  not
              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 OpenLDAP implementation.