Expose selected variables to execution environment
Provide $FILE, $UUID, $ID, $ANNOTATION and $LABEL so that the user may decide/configure which arguments will be passed to a command.

This should work on the command line.:

```
taskopen -x 'cat "$FILE" | head -n 2'
```

as well as in taskopenrc:

```
CUSTOM1_REGEX=".*\.sh"
# execute .sh files and pass UUID as first argument
CUSTOM1_CMD="$FILE $UUID"
```
