A capistrano 3 task to tag the repo after every deploy

tag_and_push_tag.cap

# Requires Capistrano 3.2 or later

namespace :deploy do
  after :finishing, :tag_and_push_tag do
    on roles(:app) do
      within release_path do
        set(:current_revision, capture(:cat, 'REVISION'))

        # release path may be resolved already or not
        resolved_release_path = capture(:pwd, "-P")
        set(:release_name, resolved_release_path.split('/').last)
      end
    end

    run_locally do
      user = capture(:git, "config --get user.name")
      email = capture(:git, "config --get user.email")
      tag_msg = "Deployed by #{user} <#{email}> to #{fetch :stage} as #{fetch :release_name}"

      tag_name = "#{fetch :stage }-#{fetch :release_name}"
      execute :git, %(tag #{tag_name} #{fetch :current_revision} -m "#{tag_msg}")
      execute :git, "push --tags origin"
    end
  end
end

Update: As of capistrano 3.2, the git:write_revision task is not necessary — cap now does this itself.

you should add .strip to user and email. else the tag's message might look a little weird (for me at least, git version 1.9.3 (Apple Git-50)).

Deployed by Jon Doe
 <[email protected]>
> to production as 20150113204036