I need to include some properties file into my typesafe config, like

```
include ${user.HOME}"/.app/db-test.conf"

```

however parser complains:

```
com.typesafe.config.ConfigException$Parse: dev/application.conf: 47: include keyword is not followed by a quoted string, but by: '${'user.HOME'}'
com.typesafe.config.ConfigException$Parse: dev/application.conf: 47: include keyword is not followed by a quoted string, but by: '${'user.HOME'}'
    at com.typesafe.config.impl.Parser$ParseContext.parseError(Parser.java:329)
    at com.typesafe.config.impl.Parser$ParseContext.parseError(Parser.java:325)
    at com.typesafe.config.impl.Parser$ParseContext.parseInclude(Parser.java:574)
    at com.typesafe.config.impl.Parser$ParseContext.parseObject(Parser.java:624)
    at com.typesafe.config.impl.Parser$ParseContext.parseValue(Parser.java:408)
    at com.typesafe.config.impl.Parser$ParseContext.parseObject(Parser.java:657)
    at com.typesafe.config.impl.Parser$ParseContext.parse(Parser.java:832)
    at com.typesafe.config.impl.Parser.parse(Parser.java:34)

```

How can I use system properties/environment variables in **include** statements?