CLI should have option for listing possible upgrade versions

[crankydillo]

I thought butterfly -l would list the possible upgrade versions. I'm not sure why I thought that since -h says its the extensions list and I'm not sure that's related to upgrade versions.

If possible, it would be good to have an option that lists the viable values for the -u parameter.

Then again, maybe I just need to spend some time with the doc:)

[fabiocarvalho777]

Option -l lists all extensions, plus their transformation templates and upgrade steps.
But you are right, it doesn't show all possible values each extension accepts with option -u. This could be a nice enhancement.