add custom commands to the cli

are you looking to implement ensemble cli plugins or a generic way to invoke say a formula custom hook?

cli plugins.

# example

    $ ensemble freeze lts:mysql

that would call a script '~/bin/ensemble-freeze' that would look something like

    #!/bin/bash

    repo_name=${1/lts://}
    bzr branch lp:principia/${repo_name} ~/my/local/formulas/${repo_name}

# example

    $ ensemble deploy-stack rails

that would call a script '~/bin/ensemble-deploy-stack' that would look something like

    #!/bin/bash

    # parse some stack config ~/.ensemble/stacks.yml

    for service in stack_services; do
      ensemble deploy local:${service}
    done

    # etc etc

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I don't think there's any special env setup needs for custom commands other than what git does to shift args appropriately.