Capture dynamic output

[Võ Minh Thu]

In #8 it is suggested that some specific output could be ignored when attempting to match an expected output, by using some kind of patterns.

This could be extended so that it would be possible to name those patterns, and the captured values could be re-used later in the shell session.

For instance:

$ docker build .
...
Successfully built [IMAGE-ID]

$ docker run [$IMAGE-ID]