# Variable Substitution

The configuration mechanism of PRIS supports basic variable substitution. Therefore it is possible to add properties to the `global.properties` file and reference the property values in any `requisition.properties` file. Properties defined in the `global.properties` can be overwritten in a `requisition.properties` file. It is also possible to use properties defined in a `requisition.properties` in a different part of the same `requisition.properties` again. An implicit property `requisition` is also available in `requisition.properties` by default.

The following examples demonstrate the use of properties as variables in a PRIS configuration. With the following configuration Nodes from the OpenNMS Demo system will be fetched. To get the information a authentication is required and provided as a global configuration parameter. The requisition for this example is named `opennmsdemo`.

``````### File: global.properties
# Start web server
# The web server listens for requests and can be accessed on TCP port 8000 of all interfaces
# URL: http://${your-ip}:8000/requisitions/${name-requisition-cfg}

driver = http
host = 0.0.0.0
port = 8000

httpUser = myUser
``````### File: opennmsdemo/requisition.properties
source.url = http://demo.opennms.com/opennms/rest/requisitions/${requisition} source.username =${httpUser}