bash, Linux: Set difference between two text files

Question

I have two files A-nodes_to_delete and B-nodes_to_keep. Each file has a many lines with numeric ids.

I want to have the list of numeric ids that are in nodes_to_delete but NOT in nodes_to_keep, e.g. .

Doing it within a PostgreSQL database is unreasonably slow. Any neat way to do it in bash using Linux CLI tools?

UPDATE: This would seem to be a Pythonic job, but the files are really, really large. I have solved some similar problems using uniq, sort and some set theory techniques. This was about two or three orders of magnitude faster than the database equivalents.

Answer 1

The comm command does that.

Answer 2

Somebody showed me how to do exactly this in sh a couple months ago, and then I couldn't find it for a while... and while looking I stumbled onto your question. Here it is :

set_union () {    sort $1 $2 | uniq }  set_difference () {    sort $1 $2 $2 | uniq -u }  set_symmetric_difference() {    sort $1 $2 | uniq -u }