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Add note about .env file to variable substitution docs (#801) 

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
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Aanand Prasad 2016-12-07 00:41:21 +00:00 committed by John Mulhausen
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compose/compose-file.md
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@ -1284,6 +1284,16 @@ 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 port mapping is `:5000` (which is of course an invalid port mapping, and will
result in an error when attempting to create the container). result in an error when attempting to create the container).
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. Both `$VARIABLE` and `${VARIABLE}` syntax are supported.
Additionally when using the [2.1 file format](compose-file.md#version-21), it Additionally when using the [2.1 file format](compose-file.md#version-21), it
is possible to provide inline default values using typical shell syntax: is possible to provide inline default values using typical shell syntax: