This is a a short way to compare 2 files on a Unix box without using DIFF. You can remove the option to output it to a file "> file3" if you want to see the output first.
If you want to see the uniq entries without the duplicates then output to a file:
sort file1 file2 | uniq -u > file3
If you want to see just the duplicate entries use "uniq -d" option then output to a file: