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+.. _environmentvars:
+
+================================================================================
+Environment variables
+================================================================================
+
+PROJ can be controlled by setting environment variables. Most users will
+have a use for the :envvar:`PROJ_LIB`.
+
+On UNIX systems environment variables can be set for a shell-session with::
+
+    $ export VAR="some variable"
+
+or it can be set for just one command line call::
+
+    $ VAR="some variable" ./cmd
+
+Environment variables on UNIX are usually removed with the ``unset`` command::
+
+    $ unset VAR
+
+On windows systems environment variables can be set in the command line with::
+
+    > set VAR="some variable"
+
+``VAR`` will be available for the entire session, unless it is unset. This is
+done by setting the variable with no content::
+
+    > set VAR=
+
+.. envvar:: PROJ_LIB
+
+    The location of PROJ :doc:`resource files<../resource_files>`.
+
+    Starting with PROJ 6, multiple directories can be specified. On Unix, they
+    should be separated by the colon (:) character. on Windows, by the semi-colon (;)
+    character.
+
+    PROJ is hardcoded to look for resource files
+    in other locations as well, amongst those are the
+    installation directory (usually ``share/proj`` under the PROJ
+    installation root) and the current folder.
+
+    You can also set the location of the resource files using
+    :func:`proj_context_set_search_paths` in the :file:`proj.h` API header.
+
+.. versionchanged:: 6.1.0
+
+    Starting with PROJ version 6.1.0, the paths set by
+    :func:`proj_context_set_search_paths` will have priority over the
+    :envvar:`PROJ_LIB` to allow for multiple versions of PROJ
+    resource files on your system without conflicting.
+
+
+.. envvar:: PROJ_AUX_DB
+
+    .. versionadded:: 8.1.0
+
+    To set the path to one or several auxiliary SQLite3 databases of structure
+    identical to the main :file:`proj.db` database and that can contain additional
+    object (CRS, transformation, ...) definitions. If several paths are
+    provided, they must be separated by the colon (:) character on Unix, and
+    on Windows, by the semi-colon (;) character.
+
+
+.. envvar:: PROJ_DEBUG
+
+    Set the debug level of PROJ. The default debug level is zero, which results
+    in no debug output when using PROJ. A number from 1-3, with 3 being the most
+    verbose setting.
+
+.. envvar:: PROJ_NETWORK
+
+    .. versionadded:: 7.0.0
+
+    If set to ON, enable the capability to use remote grids stored on CDN
+    (Content Delivery Network) storage, when grids are not available locally.
+    Alternatively, the :c:func:`proj_context_set_enable_network` function can
+    be used.
+
+.. envvar:: PROJ_NETWORK_ENDPOINT
+
+    .. versionadded:: 7.0.0
+
+    Define the endpoint of the CDN storage. Normally defined through the
+    :file:`proj.ini` configuration file locale in :envvar:`PROJ_LIB`.
+    Alternatively, the :c:func:`proj_context_set_url_endpoint` function can
+    be used.
+
+.. envvar:: PROJ_CURL_CA_BUNDLE
+
+    .. versionadded:: 7.2.0
+
+    Define a custom path to the CA Bundle file. This can be useful if `curl`
+    and :envvar:`PROJ_NETWORK` are enabled. Alternatively, the 
+    :c:func:`proj_curl_set_ca_bundle_path` function can be used.