[ILUG] File Difference

[Kieran OSullivan]

I have 2 files a.txt and b.txt. b.txt is a subset of a.txt however they are not sorted in the same order e.g. "xyz.com" will be in b.txt on line 20 and in a.txt on line 30.  I have tried using a diff command such as

diff --side-by-side --suppress-common-lines -i a.txt b.txt

This appeared to work until I took a good look at my results.

What I am looking for is a command or program, which will look at a.txt and b.txt, eliminate all the stuff in b.txt regardless of its position and display the result.

E.g a.txt ={a,b,c,d} b.txt={a,b,c}
$command a.txt b.txt 
displays {d}