Recipe: Intersection and set difference (A-B) on text files

comm
====

$ cat items1.txt
apple 
orange 
gold 
silver 
steel 
iron 


$ cat items2.txt
orange 
gold 
cookies 
carrot


$ sort items1.txt -o items1.txt ; sort items2.txt -o items2.txt
$ comm items1.txt items2.txt 
apple 
	      carrot 
	      cookies 
		                 gold 
iron 
		                 orange 
silver 
steel 

Intersection
============

$ comm items1.txt items2.txt -1 -2
gold
orange

Uncommon lines
==============
$ comm items1.txt items2.txt -3 | grep -o "[[:alnum:] ]*"
apple
carrot
cookies
iron
silver
steel 


Set difference
==========
$ comm items1.txt items2.txt -2 -3
apple
iron
silver
steel