Select added lines from file

Question

I have two versions of a file where the newer one has some lines added. The files are sorted (think of wordlists) and I want to print out the newly added lines (given file1 and file2).

I know how to write a little python or perl script to achieve this task, but can it be done with basic UNIX shell utilities, too?

Answer 1

Let a.txt be:

aaa
bbb
ccc

Let b.txt be:

aaa
bbb
ccc
ddd
eee

Using comm with -3 you can get the desired result:

comm -3 a.txt b.txt
ddd
eee

Answer 2

have a look at comm(1).

what you are looking for is

comm -13 file1 file2

or

comm -3 file1 file2