Compose: Variable substitution issue with curly braces in default values

[liamjones]

Variable substitution doesn't seem to work correctly when there is a default value which itself contains curly braces. I saw the documentation stating that $$ can be used to escape $ but didn't see anything about escaping curly braces (doubling them up didn't seem to help). Steps to reproduce:

Create a docker-compose.yml with the following contents:

````
version: '2.1'

services:

hello-world:
image: hello-world:latest
environment:
- URL_TEMPLATE=${URL_TEMPLATE:-http://example.org/{urlTemplateVariable}/some-sub-directory}
````

docker-compose up then examine the environment variables of the container (e.g. docker inspect -f "{{ .Config.Env }}" test_hello-world_1).

Expected value of URL_TEMPLATE:
http://example.org/{urlTemplateVariable}/some-sub-directory

Actual value is:
http://example.org/{urlTemplateVariable/some-sub-directory}

This also seems to cause problems when trying to override the default value from a .env file. If you add a .env like so:

URL_TEMPLATE=http://example.net

The expected value of URL_TEMPLATE is:
http://example.net

Actual value is:
http://example.net/some-sub-directory}

[shin-]

There's currently no way to escape curly braces inside a variable declaration. The evaluation will stop at the first closing brace.

[mlippert]

Just ran into this issue trying to set a default value for a variable which is supposed to be a JSON object which I'm setting as the value for an arg

args:
  FIREBASE_CONFIG: '${FIREBASE_CONFIG-''{ "projectId": "my-fbProj" }''}'

being able to backslash escape the closing brace would be really helpful, the best I can do now is error if it isn't defined in an environment variable, .env file or commandline option.

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale[bot]]

This issue has been automatically closed because it had not recent activity during the stale period.