Get the value of `key` and optionally set its expiration. `GETEX` is similar to
`GET`, but is a write command with additional options.

## Options

The `GETEX` command supports a set of options that modify its behavior:

- `EX` _seconds_ -- Set the specified expire time, in seconds.
- `PX` _milliseconds_ -- Set the specified expire time, in milliseconds.
- `EXAT` _timestamp-seconds_ -- Set the specified Unix time at which the key
  will expire, in seconds.
- `PXAT` _timestamp-milliseconds_ -- Set the specified Unix time at which the
  key will expire, in milliseconds.
- `PERSIST` -- Remove the time to live associated with the key.

@return

@bulk-string-reply: the value of `key`, or `nil` when `key` does not exist.

@examples

```cli
SET mykey "Hello"
GETEX mykey
TTL mykey
GETEX mykey EX 60
TTL mykey
```