How to run shell commands on server in Capistrano v3?

Question

I'm new to Capistrano and I've tried using Capistrano's DSL to run shell commands on the server ('run', 'execute', etc.), but it appears that it was deprecated. After searching and searching for a functional equivalent, I still am lost.

Current code:

desc 'Do something'
task :do_something
  execute 'echo sometext'
end

Output:

    cap aborted!
    undefined method `execute' for main:Object
    /Users/Justin/Dropbox/xxxx/xxxx/xxxx/Capfile:45:in `block (2 levels) in <top (required)>'
    /Users/Justin/.rvm/gems/ruby-2.0.0-p247/bundler/gems/capistrano-2dc1627838f9/lib/capistrano/application.rb:12:in `run'
    /Users/Justin/.rvm/gems/ruby-2.0.0-p247/bundler/gems/capistrano-2dc1627838f9/bin/cap:3:in `<top (required)>'
    /Users/Justin/.rvm/gems/ruby-2.0.0-p247/bin/cap:23:in `load'
    /Users/Justin/.rvm/gems/ruby-2.0.0-p247/bin/cap:23:in `<main>'
    /Users/Justin/.rvm/gems/ruby-2.0.0-p247/bin/ruby_noexec_wrapper:14:in `eval'
    /Users/Justin/.rvm/gems/ruby-2.0.0-p247/bin/ruby_noexec_wrapper:14:in `<main>'
    Tasks: TOP => deploy:do_something

Answer 1

In Capistrano v3, you must specify where you want to run the code by calling on with a list of hostnames, e.g.

task :execute_on_server do
  on "root@example.com" do
    execute "some_command"
  end
end

If you have roles set up, you can use the roles method as a convenience:

role :mailserver, "root@mail.example.com"

task :check_mail do
  on roles(:mailserver) do
    execute "some_command"
  end
end

There is some v3 documentation here: http://www.capistranorb.com/