Whilst it may have been left as an exercise for the interested reader, in the pursuit of an expeditious result and as ArunBear has already suggested, there are readily available command line tools (on *NIX & Cygwin) e.g. join - something like 
$ sort File_1 > File_1.sorted
$ sort File_2 | join File_1.sorted - -v1 -v2 > file.diff

[download]

A user level that continues to overstate my experience :-))

In reply to Re: comparing 2 files and creating third file with uncommon content by Bloodnok
in thread comparing 2 files and creating third file with uncommon content by rashichauhan

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