compatiblity guidelines

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We should prepare guidelines how to write scripts with CLI to make it future-proof.

I have at this point, for example:

• preferring to choose columns directly rather than relying on the default value for "--query",
• preferring to pass the parameter value directly instead of relying on the default, unless the value is empty

Gathering such tips will set us a contract to what extent we do not guarantee backward compatibility and will set the boundary between the user interface and the script interface.

I am afraid for example what happens when new field on API was introduced and default value for --query changed, which results in different column count and some column shift.

Command zfs list support:

-H
Used for scripting mode. Do not print headers and separate fields by a single tab instead of arbitrary white space.

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Apt-key give warning:

apt-key output should not be parsed (stdout is not a terminal)

We can enforce choose columns directly rather than relying on the default value for "--query".