docs: add environment variables reference

docs/reference/environment_variables.md

@@ -0,0 +1,63 @@
+<!--
+Copyright 2026 Columnar Technologies Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+# Environment Variables
+
+dbc supports the following environment variables:
+
+## `DBC_BASE_URL`
+
+Base URL of the driver registry to use. When set, overrides the default registries.
+
+## `DBC_OAUTH_CLIENT_ID`
+
+OAuth client ID for [`dbc auth login`](cli.md#login).
+
+## ADBC Variables
+
+dbc respects the following environment variables that [ADBC](https://arrow.apache.org/adbc) driver managers respect:
+
+### `ADBC_DRIVER_PATH`
+
+When set, drivers are installed to the specified path. See [Config Level](config_level.md#default-behavior).
+
+### `VIRTUAL_ENV`
+
+When set, drivers are installed inside the Python virtual environment specified by the value unless `ADBC_DRIVER_PATH` is set. See [Config Level](config_level.md#default-behavior).
+
+### `CONDA_PREFIX`
+
+When set, drivers are installed inside the Conda environment specified by the value unless `ADBC_DRIVER_PATH` or `VIRTUAL_ENV` are set. See [Config Level](config_level.md#default-behavior).
+
+## Other Variables
+
+dbc supports the following general environment variables:
+
+### `HTTP_PROXY`
+
+Proxy URL for `http://` requests.
+
+### `HTTPS_PROXY`
+
+Proxy URL for `https://` requests.
+
+### `NO_PROXY`
+
+Hosts that bypass the proxy.
+
+### `NO_COLOR`
+
+When set to a truthy value (e.g., `true`, `1`), disables colored output.

docs/reference/index.md

@@ -20,4 +20,5 @@ limitations under the License.
 - [Config level](./config_level.md)
 - [Driver List](./driver_list.md)
 - [Supported Platforms](./supported_platforms.md)
+- [Environment Variables](./environment_variables.md)
 - [Analytics](./analytics.md)

mkdocs.yml

@@ -63,6 +63,7 @@ nav:
       - Config Level: reference/config_level.md
       - Driver List: reference/driver_list.md
       - Supported Platforms: reference/supported_platforms.md
+      - Environment Variables: reference/environment_variables.md
       - Analytics: reference/analytics.md
 theme:
   name: material