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added suggested new example to the include 

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
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Victoria Bialas 2017-07-26 23:14:59 -07:00 committed by Victoria Bialas
parent a97df05f5b
commit 52644895c0
2 changed files with 18 additions and 59 deletions
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42
_includes/content/compose-var-sub.md
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@ -1,36 +1,27 @@
Your configuration options can contain environment variables. Compose uses the
variable values from the shell environment in which `docker-compose` is run.
For example, suppose the shell contains `EXTERNAL_PORT=8000` and you supply
this configuration:
variable values from the shell environment in which `docker-compose` is run. For
example, suppose the shell contains `POSTGRES_VERSION=9.3` and you supply this
configuration:
web:
build: .
ports:
- "${EXTERNAL_PORT}:5000"
db:
image: "postgres:${POSTGRES_VERSION}"
When you run `docker-compose up` with this configuration, Compose looks for
the `EXTERNAL_PORT` environment variable in the shell and substitutes its
value in. In this example, Compose resolves the port mapping to `"8000:5000"`
before creating the `web` container.
When you run `docker-compose up` with this configuration, Compose looks for the
`POSTGRES_VERSION` environment variable in the shell and substitutes its value
in. For this example, Compose resolves the `image` to `postgres:9.3` before
running the configuration.
If an environment variable is not set, Compose substitutes with an empty
string. In the example above, if `EXTERNAL_PORT` is not set, the value for the
port mapping is `:5000` (which is of course an invalid port mapping, and will
result in an error when attempting to create the container).
string. In the example above, if `POSTGRES_VERSION` is not set, the value for
the `image` option is `postgres:`.
You can set default values for environment variables using a
[`.env` file](../env-file.md), which Compose will automatically look for. Values
set in the shell environment will override those set in the `.env` file.
$ unset EXTERNAL_PORT
$ echo "EXTERNAL_PORT=6000" > .env
$ docker-compose up # EXTERNAL_PORT will be 6000
$ export EXTERNAL_PORT=7000
$ docker-compose up # EXTERNAL_PORT will be 7000
Both `$VARIABLE` and `${VARIABLE}` syntax are supported.
Additionally when using the [2.1 file format](compose-versioning.md#version-21), it
is possible to provide inline default values using typical shell syntax:
Both `$VARIABLE` and `${VARIABLE}` syntax are supported. Additionally when using
the [2.1 file format](compose-versioning.md#version-21), it is possible to
provide inline default values using typical shell syntax:
- `${VARIABLE:-default}` will evaluate to `default` if `VARIABLE` is unset or
empty in the environment.
@ -49,6 +40,7 @@ Compose.
build: .
command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
If you forget and use a single dollar sign (`$`), Compose interprets the value as an environment variable and will warn you:
If you forget and use a single dollar sign (`$`), Compose interprets the value
as an environment variable and will warn you:
The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.
The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.

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compose/compose-file/compose-file-v2.md
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@ -1304,40 +1304,7 @@ refer to it within the Compose file:
## Variable substitution
Your configuration options can contain environment variables. Compose uses the
variable values from the shell environment in which `docker-compose` is run. For
example, suppose the shell contains `POSTGRES_VERSION=9.3` and you supply this
configuration:
db:
image: "postgres:${POSTGRES_VERSION}"
When you run `docker-compose up` with this configuration, Compose looks for the
`POSTGRES_VERSION` environment variable in the shell and substitutes its value
in. For this example, Compose resolves the `image` to `postgres:9.3` before
running the configuration.
If an environment variable is not set, Compose substitutes with an empty
string. In the example above, if `POSTGRES_VERSION` is not set, the value for
the `image` option is `postgres:`.
Both `$VARIABLE` and `${VARIABLE}` syntax are supported. Extended shell-style
features, such as `${VARIABLE-default}` and `${VARIABLE/foo/bar}`, are not
supported.
You can use a `$$` (double-dollar sign) when your configuration needs a literal
dollar sign. This also prevents Compose from interpolating a value, so a `$$`
allows you to refer to environment variables that you don't want processed by
Compose.
web:
build: .
command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
If you forget and use a single dollar sign (`$`), Compose interprets the value as an environment variable and will warn you:
The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.
{% include content/compose-var-sub.md %}
## Compose documentation