title: Algorithm for matching strings between two large files
body: <p>I have a question regarding a search algorithm. I currently have 2 files in plain text, each one of them has at least 10 million lines.  For now, each line is a string, and I want to find each string in the first file that also appears in the second file. Is there a good way to do this efficiently?  Any suggestions from either algorithm or a special language feature is appreciated. </p>