title: How to read a large text file line-by-line and append this stream to a file line-by-line in Ruby?
body: <p>Let's say I want to combine several massive files into one and then <code>uniq!</code>  the one (THAT alone might take a hot second)</p>
  
  <p>It's my understanding that <code>File.readlines()</code> loads ALL the lines into memory. Is there a way to read it line by line, sort of like how node.js <code>pipe()</code> system works?</p>