How can we pass a variable to the alert.exec() property?

Hi,

I have a bash script I execute when an alert is triggered as define in this TICKscript:

```
var key = 'battery:capacity'

stream
|from()
.measurement('battery')
|eval(lambda: string("value"))
.as('power')
|alert()
.id('{{ .Name }}/{{ .Group }}')
.message('hello there')
.crit(lambda: "value" < 0.05)
.log('/tmp/alerts.log')
.exec('alert.sh', key, power)
```

I want to pass the 'power' as defined in the eval node, as an argument to the bash script. However when I try to register the TICKscript with the following command:

`kapacitor define alert -type stream -tick alert.tick -dbrp database_name`

I get the following error:

`invalid TICKscript: name "power" is undefined. Names in scope: stream,key,time`

Is there any way to pass down the 'power' value?

Many thanks.

Start with the alert.exec() and eval nodes in alert.tick, then reproduce the scope error with the shown kapacitor define command. Determine whether the evaluated power value can be passed to alert.sh as an exec argument; done means a supported invocation is identified or the limitation is documented.

Written by the indexing model from the issue text.