title: c# Compare two text files and generate a new one with differences
body: <p>I am looking for the best way to compare 2 text files (+-15000lines) quickly and get as output strings that are differents in the two files.
  1st one is an old inventory, new one is the current inventory and I would like to generate an third one containing strings that are different between file2 &amp; file1. (95% of the 2 files will be similar).</p>