Capturing *all* the output (both stdout and stderr) from the apt-cache command.

[Ivan Kurnosov <zerkms@zerkms.ru>]

I originally asked something similar here http://unix.stackexchange.com/q/201869/31347 but did not get the comprehensive answer.

The complete question would be: how to capture everything apt-cache outputs?

Example:

apt-cache policy non_existing_package --- here we need to capture stderr

apt-cache policy apt --- here we need to capture stdout

So is there a generic command that could capture everything and pipe further so that the call like

apt-cache policy ... | grep "something" --- was successful?

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With best regards, Ivan Kurnosov