bdemers commented on a change in pull request #82:
URL: https://github.com/apache/shiro-site/pull/82#discussion_r634411809
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File path: configuration.md.vtl
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@@ -342,6 +343,26 @@ anObject.map = $objectKey1:$objectValue1,
$objectKey2:$objectValue2
...
```
+<a name="Configuration-VariableInterpolation"></a>
+#[[######Variable Interpolation]]#
+
+You can use variable interpolation when defining values. Supported types are
environment variables, system properties and constants.
+
+For constants, use `${const:CONSTANT_NAME}`, for environment variables and
system properties, use `${ENV_VARIABLE_NAME}` or ${`PROPERTY`}.
+
+System properties and environment variables are lookup up in that order.
+
+Default values are supported in the form
`${const:CONSTANT_NAME:-default_value`}, or `${VARIABLE_NAME:-default_value}`,
as in:
+
+``` ini
+myRealm.connectionTimeout = ${REALM_CONNECTION_TIMEOUT:-3000}
+```
+
+Which will be interpreted as `myRealm.connectionTimeout = 3000` if no system
property or environment variable `REALM_CONNECTION_TIMEOUT` is defined.
+
+If no variable is found, the whole definition is passed on.
Review comment:
```suggestion
If no replacement is found, the definition will remain unchanged.
```
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