mirror of https://github.com/docker/docs.git
55 lines
2.3 KiB
Markdown
55 lines
2.3 KiB
Markdown
Your configuration options can contain environment variables. Compose uses the
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variable values from the shell environment in which `docker-compose` is run.
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For example, suppose the shell contains `EXTERNAL_PORT=8000` and you supply
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this configuration:
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web:
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build: .
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ports:
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- "${EXTERNAL_PORT}:5000"
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When you run `docker-compose up` with this configuration, Compose looks for
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the `EXTERNAL_PORT` environment variable in the shell and substitutes its
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value in. In this example, Compose resolves the port mapping to `"8000:5000"`
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before creating the `web` container.
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If an environment variable is not set, Compose substitutes with an empty
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string. In the example above, if `EXTERNAL_PORT` is not set, the value for the
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port mapping is `:5000` (which is of course an invalid port mapping, and will
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result in an error when attempting to create the container).
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You can set default values for environment variables using a
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[`.env` file](../env-file.md), which Compose will automatically look for. Values
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set in the shell environment will override those set in the `.env` file.
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$ unset EXTERNAL_PORT
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$ echo "EXTERNAL_PORT=6000" > .env
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$ docker-compose up # EXTERNAL_PORT will be 6000
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$ export EXTERNAL_PORT=7000
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$ docker-compose up # EXTERNAL_PORT will be 7000
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Both `$VARIABLE` and `${VARIABLE}` syntax are supported.
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Additionally when using the [2.1 file format](compose-versioning.md#version-21), it
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is possible to provide inline default values using typical shell syntax:
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- `${VARIABLE:-default}` will evaluate to `default` if `VARIABLE` is unset or
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empty in the environment.
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- `${VARIABLE-default}` will evaluate to `default` only if `VARIABLE` is unset
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in the environment.
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Other extended shell-style features, such as `${VARIABLE/foo/bar}`, are not
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supported.
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You can use a `$$` (double-dollar sign) when your configuration needs a literal
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dollar sign. This also prevents Compose from interpolating a value, so a `$$`
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allows you to refer to environment variables that you don't want processed by
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Compose.
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web:
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build: .
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command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
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If you forget and use a single dollar sign (`$`), Compose interprets the value as an environment variable and will warn you:
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The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.
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