These can be especially useful for administrators who want to allow Grafana viewers to quickly adjust visualizations but do not want to give them full editing permissions. Grafana Viewers can use variables.
Variables and templates also allow you to single-source dashboards. If you have multiple identical data sources or servers, you can make one dashboard and use variables to change what you are viewing. This simplifies maintenance and upkeep enormously.
## Templates
A _template_ is any query that contains a variable.
For example, if you were administering a dashboard to monitor several servers, you _could_ make a dashboard for each server. Or you could create one dashboard and use panels with template queries like this one:
```
wmi_system_threads{instance=~"$server"}
```
Variable values are always synced to the URL using the syntax `var-<varname>=value`.
Variables are listed in dropdown lists across the top of the screen. Select different variables to see how the visualizations change.
To see variable settings, navigate to **Dashboard Settings > Variables**. Click a variable in the list to see its settings.
Variables can be used in titles, descriptions, text panels, and queries. Queries with text that starts with `$` are templates. Not all panels will have template queries.
-`${var_name}` Use this syntax when you want to interpolate a variable in the middle of an expression.
-`${var_name:<format>}` This format gives you more control over how Grafana interpolates values. Refer to [Advanced variable format options]({{< relref "advanced-variable-format-options.md" >}}) for more detail on all the formatting types.
-`[[varname]]` Do not use. Deprecated old syntax, will be removed in a future release.
For example, a variable used in a regex expression in an InfluxDB or Prometheus query will be regex escaped. Read the data source specific
documentation topic for details on value escaping during interpolation.
For advanced syntax to override data source default formatting, refer to [Advanced variable format options]({{< relref "advanced-variable-format-options.md" >}}).
Grafana has global built-in variables that can be used in expressions in the query editor. Refer to [Global variables]({{< relref "global-variables" >}}) for more information.
Query variables allow you to write a data source query that might return a list of metric names, tag values, keys, server names, sensor IDs, data centers, etc.
Define a hidden constant. Useful for metric path prefixes for dashboards you want to share. During dashboard export, constant variables are made into an import option.
Data source variables allow you to quickly change the data source for an entire dashboard. Useful if you have multiple instances of a data source in for example different environments.
You can use the `Interval` type to create a variable that represents a time span (eg. `1m`,`1h`, `1d`). There is also a special `auto` option that will change depending on the current time range. You can specify how many times the current time range should be divided to calculate the current `auto` timespan.
This variable type is useful as a parameter to group by time (for InfluxDB), Date histogram interval (for Elasticsearch) or as a *summarize* function parameter (for Graphite).
Ad hoc filter variables only work with InfluxDB, Prometheus, and Elasticsearch data sources. This variable type allows you to add key/value filters that are automatically added to all metric queries that use the specified data source.
- Variable drop-down lists are displayed in the order they are listed in the variable list in Dashboard settings. Consider putting the variables that you will change often at the top, so they will be shown first (far left on the dashboard).
