How do I get only the new lines from a string (an EC2 box' console output) in Ruby?

Question

I am writing a Rake task that boots an EC2 instance and runs some commands on it.

AWS' Ruby SDK has:

instance.console_output , which returns a String of the full output (from the moment the machine booted until present).

What I really want is the "diff" between the last output and the current, so that I can just print the new lines to my local console.

I feel like there should be a tool for this somewhere in a Gem or Ruby library, but searching on Google has yielded nothing.

Any help, or am I stuck doing:

total = output.lines.length
new_lines = total - last
puts output.lines[-1..new_lines].to_a.join
last = total

in a loop?

Answer 1

Check out...

These are just a few that I've come across. There are many others.