Add a "diff" command

[diranged]

Is this a request for help?:

No, this is a feature request.

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I would love to see a ct diff command, that provides a diff between the previous generated template and the new generated template for a given chart based on the values files. Today our developers rely pretty heavily on this pattern:

$ make template > orig
$ ... vi values.yaml .. make some changes
$ make template > new && diff -b -u orig new

It's a super useful pattern for making sure you know what impact your change is going to have on a template.. but its a little convoluted to do it this way. I would love to see the ct tool provide this automatically.