I keep discovering neat things you can do in Vim.

Every Vim user knows you can save the current buffer with :w.

But you can also pass a filename: :w ~/my.backup. Then the contents of the current buffer are written to that file. It happens in the background, so to speak – the filename of the current buffer doesn't change, unlike :saveas.

If you make a visual selection first, only those lines are written to the specified file.

I've used this for two things:

To copy and paste between two Vim sessions. I do :w /tmp/x in one Vim, and :r /tmp/x (or :read /tmp/x) in the other.

And just now, I realized I could use it to break one file into two. I had some secret authentication info alongside some experimental code. I wanted to start version controlling that code, so I needed to extract the secrets. I visually selected those lines, did :w ~/.secret.rb and then replaced the lines with require "~/.secret.rb". Reminds me of the useful :Rextract in Rails.vim, but built in.

Something else I discovered in :help :w, but haven't put to use yet, is :w >> /some/file to append.