Using Context-Sensitive Variables in Charts
When editing charts from a service, role or host status or charts page, or when adding a chart to a status page, a set of context-sensitive variables (each beginning with '$') will be displayed below the query box on the Chart Builder page.
For example, you might see variables similar to those in the query below:
$HOSTNAME portion of the query string.
$HOSTNAME is a variable that will be resolved to a
specific value based on the page before the query is actually issued. In
$HOSTNAME will become
Context-sensitive variables are useful since they allow portable queries to be written. For example the query above may be on the host status page or any role status page to display the appropriate host's swap rate. Variables cannot be used in queries that are part of user-defined dashboards since those dashboards have no service, role or host context.