> ## Documentation Index
> Fetch the complete documentation index at: https://www.osohq.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Polar Built-In Constants

Polar provides built-in "constants", which can be referenced in rules and then evaluated at runtime.

## `@current_unix_time`

The `@current_unix_time` keyword can be used to refer to the unix time (the number of seconds that have elapsed since January 1, 1970 at midnight UTC) at the time of a query.

`@current_unix_time` returns an `Integer`.

For example, if you have a fact `expires_at(File:foo, 1670280790)` indicating the time that the "foo" file expires, you could use this for time-based access:

```polar theme={null}
has_permission(_: Actor, "read", file: File) if
  expires_at(file, time) and @current_unix_time < time;
```