Fastest way of finding differences between two files in unix?

Question

I want to find the difference between two files and then put only the differences in a third file. I saw different approaches using awk, diff and comm. Are there any more ?

eg.Compare two files line by line and generate the difference in another file

eg.Copy differences between two files in unix

I need to know which is the fastest way of finding all the differences and listing them in a file for each of the cases below -

Case 1 - file2 = file1 + extra text appended. Case 2 - file2 and file1 are different. 

Answer 1

You could try..

comm -13 <(sort file1) <(sort file2) > file3 

or

grep -Fxvf file1 file2 > file3 

or

diff file1 file2 | grep "<" | sed 's/^<//g'  > file3 

or

join -v 2 <(sort file1) <(sort file2) > file3 

Answer 2

Another option:

sort file1 file2 | uniq -u > file3 

If you want to see just the duplicate entries use "uniq -d" option:

sort file1 file2 | uniq -d > file3