Align selected region in emacs

For example I write code

if Foo do
  # do something
end

And then, I paste in my code many l开发者_高级运维ines.

if Foo do
  # do something
# do something
# do something
# do something
# do something
end

How I can fast align added lines?

Do you want to align automatically on insert, or you want to align it later? For later you can use indent-region function (bound to C-M-\). For automatic align on insert you can use following recipe (I don't remember where I took it, so I'll refer to my config) - see lines 45-66. You will need to add more modes to yank-indent-modes, but concrete mode should provide working indent function.