UNIX Command : comm

Description:

comm - compare two sorted files line by line and write to standard output, the lines that are common, plus the lines that are unique. 

Syntax:

comm [options].. File1 File2

Options:

-1 suppress lines unique to file1.

-2 suppress lines unique to file2.

-3 suppress lines that appear in both files.

For Example:
Consider I have 2 sorted files.

Nirmals-MBP:nirmalg$ cat a.txt
a
b
c
d

Nirmals-MBP:nirmalg$ cat b.txt
c
d
Nirmals-MBP:nirmalg$

To get the common lines from both the files.

Nirmals-MBP:nirmalg$ comm -12 a.txt b.txt
c
d
Nirmals-MBP:nirmalg$

To get uncommon lines between both the files.

Nirmals-MBP:nirmalg$ comm -23 a.txt b.txt
a
b
Nirmals-MBP:nirmalg$