I would like to be able to define additional environment variables based on the output of a command. As a practical example, I would like to set an environment variable HOSTNAME, with the result of the command hostname -s as the value.
I could implement this on my own, but I would like to get your opinion about the right way to configure this.

Possibilities which come to my mind:

1. New configuration element

[tasks.envs]
    cmdenvs = [ [ "HOSTNAME", "hostname", "-s" ] ]

2. Extension of the existing envs, e.g. with a macro/placeholder, which evaluates the additional arguments:

[tasks.envs]
    envs = [ [ "HOSTNAME", "@exec", "hostname", "-s" ] ]